Marine fire ecology

April 28th, 2024 No comments

We have recently published a paper emphasizing the importance of fire ecology in marine ecosystems [1]. Fires occur in terrestrial ecosystems, but marine ecosystems are also affected and thus play a role in the ecology of fire. Fire by-products travel to the oceans by land (e.g., ashes and sediments through runoff and rivers) and by air (smoke and aerosol deposition). Wildfires enhance the transport of carbon and nutrients from land to sea, thereby altering global carbon and nutrient cycling. For instance, part of the black carbon (charcoal) from wildfires is transported to oceans and sinks into deep waters. The increase in nutrients in the ocean often enhances phytoplankton productivity, especially in iron (Fe)-limited waters. These effects impact marine biota; some species may benefit from increased nutrients while others may suffer negative consequences. Our current understanding of how fires impact marine ecosystems is primarily anecdotal; marine fire ecology is a new research area that requires further study.

Schematic representation of the interaction between land (where fires occur), freshwater and the atmosphere (where fire byproducts are transported), and the ocean. From [1]

References

[1] Riera R & Pausas JG 2024. Fire ecology in marine systems. Trends Ecol. Evol. 39: 221-224. [doi | sciencedirect | pdf]

Pico picapinos

March 31st, 2024 No comments

Una de las razones para no cortar los árboles muertos después de un incendio, es por que las condiciones semi-forestales que generan son hábitat de fauna forestal, como por ejemplo, los picos picapinos (Dendrocopos major). Aquí un picapinos en un pinar de pino carrasco (Pinus halepensis) el incendio de Bejís (2022, Castelló); video 2/2024 (de hecho, se ve uno y se oye otro). Otros beneficios de no cortar los árboles muertos se explicaron aquí y aquí.

Beneficios de no cortar los árboles después de un incendio [TheConversation | post]

Carpinteros de la madera quemada [Quercus | pdf]

Seed dormancy release and summer temperatures

February 18th, 2024 No comments

In Mediterranean ecosystems, fire breaks the dormancy in many species and stimulates germination in the postfire environment [1]. Both the smoke and the heat of the fire may be responsible for breaking dormancy [1]. Cistaceae species are typical examples of species with this heat-released dormancy [1, 2], together with many legumes. Despite fire is a much more powerful driver of dormancy release than the summer heat (figure 9 in [1] and figure 2 in [2]), there are still people aiming to demonstrate the role of summer temperatures in dormancy release in Cistaceae. A recent research team studied the germination of 12 Cistacea species and compared the effect of fire-type heat in seeds submitted to a summer heat treatment (50/20o C for a month) and in seeds without this summer treatment [3]. They concluded that high summer temperatures are needed for maximum germination in the presence of fire [3]. A reanalysis of their data suggests that not only are summer temperatures inefficient at releasing dormancy, but they also reduce postfire germination [4]. The applied summer heat treatment reduced the germination (%) in the control (H-) and in all fire treatments, and for all species (Fig. 1 below). And for the seeds that germinate, those under summer heat tended to germinate slower than those that did not suffer the summer heat (Fig. 2 below). In conclusion, fire increases the germination of Cistaceae seeds in contrast to summer-type heat, i.e., the great fitness benefits of fire are unmatched by the summer heat [4].

Fig. 1. Germination with no summer heat (x-axis; ~ 20o C for a month) and with summer heat (y-axis, 50/20o C altering for 12 h, and during a month) in 12 Cistaceae species with different fire treatments. All fire heat treatments were 100o C for 10 min applied as follows: H-, no fire heat (black); HB, fire heat before summer (green); HA, fire heat treatment after summer (red); HBA, fire heat before and after the summer (unrealistic scenario; blue). The results suggest that applying a strong summer heat treatment (52/20o C for a month) reduces the germination (%) in the control (H-) and in all fire treatments and for all species. From [4].


Fig. 2. Number of days to the first germination (T0, left) and to reach 50% of the final germination (T50, right) with no summer heat (x-axis, control) and with summer heat (y-axis, treatment), and with different fire treatments (colors; see figure above) for 12 Cistacea species (12 points for each color). The results suggest that summer heat, if any, tends to increase the time to germination.

References

[1] Pausas J.G. & Lamont B.B. 2022. Fire-released seed dormancy – a global synthesis. Biological Reviews 97: 1612-1639.  [doi | pdf | supp. mat. | data (figshare)]

[2] Moreira B. & Pausas J.G. 2012. Tanned or burned: The role of fire in shaping physical seed dormancy. PLoS ONE 7(12): e51523. [doi | plos | pdf]

[3] Luna B, Piñas-Bonilla P, Zavala G, Pérez B. 2023. Timing of fire during summer determines seed germination in Mediterranean Cistaceae. Fire Ecology 19: 52.

[4] Lamont BB, Burrows GR, Pausas JG 2024. Fire-type heat increases the germination of Cistaceae seeds in contrast to summer heat. Fire Ecology 20:14 [doi | pdf]

More on seed dormancy: A review | a glossary | bet-hedging & best-bet | smoke-released dormancy 

Millán Millán (1941-2024)

January 13th, 2024 No comments

Millán Millán Muñoz (Granada 1941 – Valencia 2024), físico atmosférico por la Universidad de Toronto e ingeniero industrial por la Universidad del País Vasco. Durante su tiempo en Canadá desarrolló diversos instrumentos para detectar metales, contaminantes y plumas de volcanes, que aun se utilizan actualmente. También trabajó en la dispersión de contaminantes, tanto en Canadá como en España. En España fue el director, y alma mater, de la Fundación CEAM (Valencia, 1991-2012), donde realizó estudios muy novedosos y de gran calado para entender la dinámica atmosférica en la cuenca Mediterránea. Se enfocó en entender esa dinámica y su relación con la meteorología, la dispersión de contaminantes, la calidad del aire, el cambio climático y el ciclo del agua. En este marco, una de sus aportaciones importantes fue demostrar científicamente que las pérdidas de tormentas en la costa Mediterránea eran debidas a la urbanización y destrucción de los ecosistemas de la costa; es decir, la causa de las pérdidas de tormentas no es directamente el cambio climático sino al mal uso del territorio. Llegó a cuantificar la cantidad de lluvia anual que hemos perdido en la costa valenciana por el mal uso del territorio.

Persona extremadamente lista, con gran intuición y capacidad para entender procesos; era muy crítico con los estudios tradicionales basados en correlaciones o en modelos de grano grueso (la mayoría). Era sincero, y decía las cosas que pensaba sin demasiadas formalidades, aunque no fueran las cosas que a la gente le gustaba oír; esto le generó algunas enemistades. Él mismo se definía como “granaíno malafolla”, pero en el fondo, era muy buena persona y con muy buen sentido del humor. Quizá por su carácter y sinceridad ha sido frecuentemente infravalorado.

Falleció ayer 12 de enero. Nos ha dejado un legado muy importante que aun tenemos que asimilar del todo. Encontraremos a faltar su sabiduría. Que descanse en paz.

Millán Millán. Origen de las fotos, arriba: Mónica Torres (tecnicaindustrial.es) 2011, JG Pausas 2017 (Mijares); abajo: EPDA 2019 (izquierda y centro) y Las Provincias 2024.

Más información:

Millán en Wikipedia | Entrevistas: 2011 (pdf),  2017,  2019 | Charla 2023 (video) 

Millan Millan and the Mystery of the Missing Mediterranean Storms (2023)

Millán, M.M. 2014. Extreme hydrometeorological events and climate change predictions in Europe. Journal of Hydrology 518, Part B, 206–224. | doi

Pausas, J.G. & Millán, M.M. 2019. Greening and browning in a climate change hotspot: the Mediterranean Basin. BioScience 69, 143–151.  doi | oup | blog | pdf 

Honoring Wallace

January 6th, 2024 No comments

Alfred Russel Wallace was a great naturalist who independently discovered natural selection; it is also recognized for his foundational work in evolutionary biogeography. While often overshadowed by Darwin’s popularity, Wallace’s scientific contributions remain significant and influential. James T. Costa’s recent book, ‘Radical by Nature’ (Princeton University Press, 2023), gives full credit and details on Wallace’s outstanding contribution to science.

Wallace laid out the first ideas of the evolution of species in 1855 with his Sarawak Law paper [1] when he was living (traveling) in the Malayan archipelago; the article likely inspired scientists of that time, including Darwin. Later, in 1858, Wallace produced another paper describing the mechanism of natural selection. But before sending it to the publisher, he sent the draft to Darwin for comments. Darwin was working on his book (On the origin of species) and realized that they both had independently arrived at the same conclusion (i.e., evolution by natural selection), so he was worried that Wallace was going to publish it first. Finally, with the help of Lyell & Hooker, they agreed to co-authored the famous paper that first described the mechanism of natural selection (Darwin & Wallace 1858 [2]). This paper, in fact, was not written together but included texts written independently from both to show that they arrived at the same idea (article edited by Lyell & Hooker). Wallace generously accepted Darwin’s priority. In fact, Wallace had started to write a book on the origin of species but put it down after knowing that Darwin was working on a similar book; instead, he dedicated his time to further exploring the Malayan archipelago (from 1854 to 1962). Darwin published his book On the origin of species in 1859, which described in great detail, and popularised the concept of natural selection.

Throughout his life, Wallace was not only a strong supporter of natural selection and Darwin’s ideas but also made significant contributions to other aspects of evolutionary thinking. For example, modern views on evolutionary biogeography, sexual selection, evolutionary mimicry, aposematism, and some aspects of the speciation process (such as allopatry, reinforcement and the Wallace effect) align more closely with Wallace’s ideas than with Darwin’s. Wallace also made numerous contributions to other fields, including anthropology, geology, physical geography, climatology, taxonomy, and systematics. He is often considered the first humanitarian scientist due to his strong support for social justice. He wrote papers on a variety of topics, including land reform, monetary reform, women’s rights, environmental conservation, and critiques of capitalism, militarism, and imperialism. One controversial aspect of his life was his belief in spiritualism, which made him believe that the human mind was not the product of natural selection!!. However, this should not be used to minimize the numerous contributions to evolutionary theory. And honoring Wallace does not need to detract from the recognition of Darwin’s major contributions.

So, Costa’s book is enjoyable and very welcome! 

References

[1] Wallace A.R. 1855. On the law which has regulated the introduction of new species. Annals and Magazine of Natural History 16, 184–196. [Sarawak Law paper]

[2] Darwin C.R. & Wallace A.R. 1858. On the tendency of species to form varieties; and on the perpetuation of varieties and species by natural means of selection. Proc. Linnean Soc: Zoo. 3: 45–62. [one of the most important papers in biology!]

The geological history of fire

December 19th, 2023 No comments

Fire is unique to Earth; it is a characteristic of our planet. As far as we know, no other planet has fire. Here is a video explaining the geological history of fire, including its relation to the evolution of pines and grasses. It concludes that “without fire, there would probably be no grasslands and the forest of the world would likely have a lot less diversity“. By PBS Eons.

References

  • Pausas J.G. & Keeley J.E. 2009. A burning story: The role of fire in the history of life. BioScience 59: 593-601 [doi | OUP | pdf]
  • He T, Pausas JG, Belcher CM, Schwilk DW, Lamont BB. 2012. Fire-adapted traits of Pinus arose in the fiery Cretaceous. New Phytol. 194: 751-759. [doi | wiley | pdf | suppl.]

POSTDIV: Postfire biodiversity database

December 10th, 2023 No comments

In the summer of 2012, two wildfires affected Mediterranean ecosystems in the eastern Iberian Peninsula, the Andilla fire and the Cortes fire [1]. The size of these fires (> 20,000 ha each) was at the extreme of the historical variability (megafires sensus [2]). In 2013, we set up 12 plots per fire, covering burned vegetation at different distances from the fire perimeter and unburned vegetation. In each plot, we followed the postfire recovery of arthropods, reptiles (including their ectoparasites), and plants for 2 to 5 years. Here we present the resulting database (POSTDIV) of taxon occurrence and abundance in the burned and unburned areas [3]. Currently, POSTDIV totals 19,906 records for 457 arthropod taxa (113,681 individuals), 12 reptile taxa (503 individuals), 4 reptile parasites (234 individuals), and 518 plant taxa (cover-abundance). We provide examples in the R language to query the database.

Wildfires 2012
The two wildfires occurred simultaneously in Valencia during the 2012 summer (photo: 30 Junio 2012).
POSTDIV database structure. The database is composed of six data tables (blue boxes). For more details, see [3].

References

[1] Pausas J.G. 2012. Life 15 days after the large fires in Valencia. jgpausas.blogs.uv.es/2012/07/22/

[2] Pausas J.G. & Keeley J.E. 2021. Wildfires and global change. Front. Ecol. Environ. 19: 387-395. [doi | wiley | pdf]

[3] Pausas et al. 2023. Postfire biodiversity database for eastern Iberia. Sci Data 10:872 [doi | pdf | pdf | data: figshare

Afforestation, wildfires, and C emission in Chile

November 30th, 2023 No comments

During the 2016/17 fire season in Chile, wildfires burned about 600,000 ha, a record for the region. The fact that the region was covered by large and dense tree plantations that created a continuous fuel bed, contributed to these massive wildfires (Fig. 1), together with an intense drought with strong head waves. That is, afforestation as established in Chile can lead to larger and more severe fires under warming conditions [1]. These mega-fires have multiple socioeconomic consequences. A recent analysis suggests that afforestation generates the emission of large amounts of greenhouse gases (they act as a net carbon source) while native forests act as a sink (Figure 2). 

Figure 1: Analysis of the areas affected by fires according to types of use (forest plantations, native forest, Scrubland + pastures, and agricultural areas), in relation to what is available in each of the 4 regions that have burned the most (V, RM, VI, VII are: Valparaiso, Metropolitana, O’Higgins, and Maule). Positive data means that fire has positively selected this type of use (it has burned more than expected by the area it occupies); the negative data indicates that fire tends to avoid such land use. There is a strong tendency for plantations to burn more than expected according to their abundance in the landscape (positive values), while native forests, scrub, or agricultural areas are burned similarly or less than expected according to their abundance (negative values). The region VII (Maule) is the most extreme in the positive selection of plantations and negative of other uses. Elaborated based on official SIDCO-CONAF data (Chile) [2].

Figure 2, left: Forest plantations act as a net carbon source in contrast to the native forests (sink). Shown is the carbon balance (million tons of CO2-equivalent; including CO2, CH4, and N2O) for the period 1990–2018, including capture (biomass increment and long-lived harvested wood products) and emissions (short-lived harvested wood products and wildfires), for native forests and for plantations in Chile. Dots are mean annual values (the outlier for plantations corresponds to the 2017 mega-fires). From [3]

Figure 2, right: The contribution of tree plantations to burned area is increasing. Shown are the area of plantations burnt annually (ha, in orange) and the proportion of the area of plantations burnt annually in relation to the total area burnt, including native forests, shrublands, and grasslands (%; data in black symbols, fit in red for the period 1984–2022). Note that the proportion of plantations burnt increases more steadily than the area of plantations burnt, probably as an indication that plantations have become increasingly more fire-prone compared with other land uses. From [3]

Reference
[1] Leverkus A.B., Thorn S., Lindenmayer D.B. & Pausas J.G. 2022. Tree planting goals must account for wildfires. Science 376: 588–589. [doi | science | pdf]

[2] Incendios en Chile 2017, jgpausas.blogs.uv.es/2017/02/10

[3] Gómez-González S, Miranda A, Hoyos-Santillan J, Lara A, Moraga P & Pausas J.G. 2024. Afforestation and climate mitigation: lessons from Chile. Trends Ecol. Evol. 39(1) [doi | pdf]

 

More on Chile | Afforestation 

Entrevista

October 19th, 2023 No comments

En 2021, “The Emergency Program” (www.emerprogram.com) me hizo una entrevista. Aquí la entrevista dividida en 5 videos (sin editar; duración en minutos:segundos):

  1. Regímenes de incendios sostenibles, 8:30 [youtube]
  2. Quemas prescritas, 5:04 [youtube]
  3. Regímenes de incendios y estrategias de las plantas, 15:50 [youtube]
  4. Cambios en los regímenes de incendios, regeneración, y biodiversidad [youtube]
  5. Cambio climático e incendios forestales, 3:18 [youtube]

Conferencia: Incendios y biodiversidad

September 17th, 2023 No comments

El día 16 de septiembre de 2023 impartí una conferencia titulada ‘Incendios forestales y biodiversidad’ en la sede de Ecologistas en Acción (Madrid). Aquí está disponible (incluye la sesión de preguntas al final).

We need mechanistic vegetation models!

August 19th, 2023 No comments

The journal Science recently rejected reply letters from at least 3 groups of top scientists to a poor paper they published (Higgins et al. 2023). Science only accepted comments as footnotes to the original article (termed eLetters). It is disappointing that a top journal like Science published a modelling paper that does not simulate the most important mechanisms of the system the authors aim to model. However, it is even more disappointing that Science is not more open to scientific debate, which is an important part of the scientific process. Therefore, we have added a brief comment to the poor paper as an eLetter in Science (also available in PDF) as the only way to warn the readers of some shortcomings (there are more that we hope will be published elsewhere). Below is a copy of our eLetter. 

We need mechanistic models to explain Alternative Ecosystem States in tropical vegetation

by William J. Bond & Juli G. Pausas

In their paper Limited climatic space for alternative ecosystem states in Africa (Science 8 June 2023, p. 1038), Higgins et al. use a plant growth model applied to species distribution and climate variables, to argue that Alternative Ecosystem States (AES) have limited importance in Africa. However, their model does not account for key ecological factors in Africa such as large herbivores and fires (1, 2). Their exclusion raises serious doubts about the model’s validity. Higgins et al. emphasise how well their model predicts the distribution of forests and savannas. However there is a poor fit in the maps predicting optimal areas for several growth forms (3, 4). The model failed to identify the major areas of shrub dominance in Africa, fynbos and karoo shrublands in the south-west and steppe shrublands in north-east Africa (their Figure 1). Succulents are predicted for the north African Mediterranean coast where there are none (and for large areas of southern Africa) presumably by erroneous extrapolation from succulent distribution in South Africa. Optimal ‘relative climatic suitability’ for C4 grasses is predicted for the southern margins of the Sahara desert (their Figure S2) but not the vast savannas that cover most of the rest of the continent.

Higgins et al. argue that the maps they derived show limited potential for tree growth in areas they identified as climatically limited savannas contradicting other studies identifying large areas of mesic savannas as suitable for large-scale tree planting. However, their model fails to predict a forest-suitable environment in areas supporting large-scale commercial forestry plantations, e.g. in southern Africa (5). In fact, it is unknown how much of the areas they predict as savannas, and are actually savannas (“true savanna predictions”; in their Fig. 3), could sustain a forest, and would therefore be examples of AES. Higgins et al. gloss over additional evidence for AES including paleoecological studies of system shifts between savanna and forest, hysteresis, historical studies, remote sensing and multi-decadal fire suppression experiments, both natural and by design, in Africa and elsewhere showing major ecosystem shifts typically linked to fire suppression or addition (6-10).

We conclude that Higgins et al. cannot be used as a basis for interpreting alternative ecosystem states, the potential for tree planting in Africa, or whether climate and physical site factors determine forest and savanna distribution. We suggest that the problem may lie in assuming that the distribution of species represents a fundamental niche and not a realised niche so that their apparently physiologically based model is really a rather complex correlative model following a long line of predecessors. The models lack seedling and sapling stages, widely considered to be key to whether trees can escape the flame zone and thereby exist in savannas or be restricted to forests (11). Fire is not included as a source of biomass loss. Nor is there any explicit consideration of shade, a major factor separating forest from savanna species (12). It lacks most of the fundamental mechanism to simulate a dynamic system such as African ecosystems. Exploration of the dynamic response of the model, for example to changing CO2 from 400 ppm to 280, might help reveal its sensitivity to environmental drivers outside those used to derive physiological parameters from inverse models of contemporary plant species distributions. Process-based models based on measured physiological, and fire response traits, are more appropriate tools for exploring the potential for alternative stable states because they test what could be and are not restricted by what is (13-15).

Higgins et al. model contributes little to the understanding of the processes assembling African ecosystems, and cannot be taken as evidence against AES. In our changing world, we need more mechanistic and dynamic models before casting aside all evidence for fire and herbivores limiting distributions of forests (2).

References

  1. N. Owen-Smith, Only in Africa: The Ecology of Human Evolution (Cambridge University Press, Cambridge, 2021).
  2. W. J. Bond, Open Ecosystems: Ecology and Evolution Beyond the Forest Edge (Oxford University Press, 2019).
  3. F. White, “The vegetation of Africa: a descriptive memoir to accompany the UNESCO/AETFAT/UNSO vegetation map of Africa by F White” (Natural Resources Research Report XX, UNESCO, Paris, France, 1983), pp. 1876-1895.
  4. D. A. Keith, J. R. Ferrer-Paris, E. Nicholson, R. T. Kingsford, Eds., IUCN Global Ecosystem Typology 2.0: descriptive profiles for biomes and ecosystem functional groups (IUCN, International Union for Conservation of Nature, 2020).
  5. Z. Du, L. Yu, J. Yang, Y. Xu, B. Chen, S. Peng, T. Zhang, H. Fu, N. Harris, P. Gong, A global map of planting years of plantations. Sci Data. 9, 141 (2022).
  6. L. Gillson, Evidence of a tipping point in a southern African savanna? Ecol. Complex. 21, 78-86 (2015).
  7. Z. S. Venter, M. D. Cramer, H. J. Hawkins, Drivers of woody plant encroachment over Africa. Nat. Commun. 9, 2272 (2018).
  8. J. C. Aleman, O. Blarquez, H. Elenga, J. Paillard, V. Kimpuni, G. Itoua, G. Issele, Staver A. Carla, Palaeo-trajectories of forest savannization in the southern Congo. Biol. Lett. 15, 20190284 (2019).
  9. J. G. Pausas, W. J. Bond, Alternative biome states in terrestrial ecosystems. Trends Plant Sci. 25, 250-263 (2020). https://doi.org/10.1016/j.tplants.2019.11.003 
  10. H. Beckett, A. C. Staver, T. Charles-Dominique, W. J. Bond, Pathways of savannization in a mesic African savanna-forest mosaic following an extreme fire. J. Ecol. 110, 902-915 (2022).
  11. C. P. Osborne, T. Charles-Dominique, N. Stevens, W. J. Bond, G. Midgley, C. E. R. Lehmann, Human impacts in African savannas are mediated by plant functional traits. New Phytol. 220, 10-24 (2018).
  12. T. Charles-Dominique, G. F. Midgley, K. W. Tomlinson, W. J. Bond, Steal the light: shade vs fire adapted vegetation in forest-savanna mosaics. New Phytol. 218, 1419-1429 (2018).
  13. W. J. Bond, F. I. Woodward, G. F. Midgley, The global distribution of ecosystems in a world without fire. New Phytol. 165, 525-538 (2005).
  14. S. I. Higgins, S. Scheiter, Atmospheric CO2 forces abrupt vegetation shifts locally, but not globally. Nature. 488, 209-212 (2012).
  15. G. Lasslop, S. Hantson, S. P. Harrison, D. Bachelet, C. Burton, M. Forkel, M. Forrest, F. Li, J. R. Melton, C. Yue, S. Archibald, S. Scheiter, A. Arneth, T. Hickler, S. Sitch, Global ecosystems and fire: multi-model assessment of fire-induced tree cover and carbon storage reduction. Global Change Biol. 26, 5027-5041 (2020).

“I would rather discover one cause than gain the kingdom of Persia”, Democritus (460-370 BC)

Update: Aleman and collaborators have also published an eLetter in response to the paper by Higgins. Here is their eLetter: link | PDF

The history of evolutionary fire ecology

August 9th, 2023 No comments

Evolutionary fire ecology is a relatively young discipline. The idea that fire acts as an evolutionary force contributing to shaping species traits started a century ago, but has not been widely recognized until very recently. Among the first to realize this force include E.B. Paulon, R.D. Guthrie, and E.V. Komarek in animals, and W.L. Jepson, W.W. Hough, T.M. Harris, P.V. Wells and R.W. Mutch in plants (all earlier than 1970). Our recent paper [1] is a tribute to these researchers that were ahead of their time in their evolutionary thinking.

Since them, evolutionary fire ecology has percolated very slowly into the mainstream ecology and evolutionary biology; in fact, this topic is still seldom mentioned in textbooks of ecology or evolution. Currently, there is plenty of evidence suggesting that we cannot understand the biodiversity of our planet without considering the key evolutionary role of fire [2]. We also provide thoughts on future direction of this discipline.

Traits mentioned in the article as potential adaptive to fire-prone environments are [1]:

  • Traits that enhance survival
    Resprouting traits (plant survival): Root crown, Lignotuber, Woody rhizomes, Epicormic resprouting, Sunken stem buds, Smoke-induced nutrient translocation
    Stem survival: Thick (outer) bark, Reduced flammability
  • Traits that enhance reproduction and recruitment
    Heat-released dormancy, Smoke-released dormancy, Seed traits enhancing seed survival, Serotiny, Fire-stimulated flowering, Increased flammability (chemically or structurally), Precocity (ie early reproduction), Elaiosomes (ant-dispersal)

In our search for early researchers with an evolutionary view of fire [1], we may have missed some women and non-English speaker researchers; if so, we would appreciate feedback on such omissions.

Figure 1. Two of the manzanitas from Jepson (1916, Madroño 1:3-12): Arctostaphylos glandulosa (left) and Arctostaphylos nummularia (right). The former is an obligate resprouter (note the basal burl) and the latter is an obligate seeder (note the even-aged cohort). Manzanitas were among the first plants that made scientists think about the role of fire in plant evolution.

[1] Pausas JG & Keeley JE. 2023. Evolutionary fire ecology: an historical account and future directions. BioScience. [doi | pdf]

[2] Keeley JE & Pausas JG. 2022. Evolutionary ecology of fire. Ann Rev Ecol, Evol, Syst 53: 203-225. [doi |eprint | pdf]

Chatbots y Sócrates

July 9th, 2023 1 comment

Irene Vallejo (El infinito en un junco, Ediciones Siruela, 2022) nos recordaba que en la antigua Grecia, la oralidad era la principal vía de transmisión cultural. Cuando se empezó a escribir libros, mucha gente les tenía miedo, incluidos filósofos tales como Sócrates (él nunca escribió un libro). En esa época se pensaba que los libros dañarían a la humanidad, porque cualquiera podía leerlos y pretender ser sabio, sin serlo. Los libros permitían engañar. Además, se sugería que los libros frenaban el diálogo de ideas y fosilizaban el dinamismo de la oralidad.

Posteriormente, en el siglo XV, cuando Gutenberg introdujo la imprenta en Europa (desde China), la humanidad disponía de una herramienta para difundir rápidamente la información. Se hizo posible engañar masivamente. Sin embargo, pocas personas actualmente piensan que los libros y la imprenta han dañado a la humanidad.

Con el espectacular aumento actual en la generación de texto a través de chatbots basados en inteligencia artificial (IA) también han aparecido los temores al engaño masivo. Un ejemplo de tales chatbots es el ya famoso chatGPT. Incluso se ha sugerido, de manera alarmista, que pueden llegar a destruir la humanidad. Pero al igual que los libros y la imprenta, debemos suponer que las ventajas superarán las desventajas. De hecho, la historia ya nos ha demostrado, de manera recurrente, lo peligrosa que puede ser la estupidez natural; no hay evidencias de que la IA sea peor. En cualquier caso, no hay marcha atrás, los chatbots (o más genéricamente, los Large Language Models o LLM) han llegado aquí para quedarse, y debemos generar las condiciones para asegurarnos de que su crecimiento vaya en la mejor dirección para la humanidad. Los chatbots son herramientas muy útiles para un sinfín de cosas (especialmente resumir o compilar información), pero no para generar nueva información. Un mal uso podría llevar a reducir la creatividad, la innovación, y el pensamiento crítico. Es decir, debemos usar y gestionar la IA de manera inteligente! Es probable que se requiera una legislación internacional para asegurar ciertos límites y una transparencia de los algoritmos. De hecho, sería deseable que se elaboraran LLM de código abiertos, igual que hay entornos estadísticos y de programación de código abierto, para asegurar una evolución independiente de las grandes corporaciones.

Nos ha tocado vivir un salto cualitativo, para el que, como es esperable, no estamos preparados. Este salto es quizás comparable a la invención de los libros y la imprenta; las tres invenciones tienen el objetivo de propagar textos escritos. Y con todo ello, hemos entendido un poco mejor a Sócrates.

 

Sócrates, Atenas

Disturbance in human societies

June 2nd, 2023 No comments

Like ecosystems, humans societies are also subject to recurrent disturbances, that is, they are subject to discrete events that abruptly affect the functioning of a society [1]. There is a variety of such societal disturbances, including hurricanes, floods, epidemics, nuclear accidents, earthquakes, and wars among others (Table 1). Very large or severe disturbances are infrequent and unpredictable. Yet societal disturbances are intrinsic to human societies; they have occurred through the entire human history and will continue to occur in the future. Societal disturbances can temporarily disrupt the functioning of societies. However, when those disturbances are frequent, societies adapt to them and thus disturbances contribute to shape cultural evolution. That is, societal disturbances have a cost at short temporal scales, but they can build up resilience at mid- to long-term scales. 

 

Table 1. Examples of disturbances that affect the functioning of human societies. From [1]

Disturbance typeExamples
MeteorologicalDroughts, hurricanes, floods, ice storms, heatwaves
BiologicalEpidemics, pandemics
Accidental (technological)Nuclear accidents, urban fires, power blackouts
Socio-politicalWars, terrorist attacks
GeologicalEarthquakes, volcanoes, tsunamis
VirtualStock market crash, internet crash, cyberattacks
ExtraterrestrialMeteorite impact

Fig. 1. Comparison among five disturbances that produced large numbers of fatalities at the global scale, over the last 4000 years of human history (from 2000 BP to 2020). Note the log scale. From [1]

Fig. 2. Frequency distribution of the five disturbances together included in Fig. 1. The vertical dotted line is the 99% quantile and suggests that 1% of these disturbances accounts for 87% of fatalities over the last 4000 years of human history (from 2000 BP to 2020). Note the log scale. The frequency distribution (of the raw data) is strongly skewed (skewness = 24.98) with a long tail (Pearson’s Kurtosis = 789.73). From [1]

References

[1] Pausas JG & Leverkus A. 2023. Disturbance ecology in human societies. People and Nature [doi | wiley | pdf]

Herbivores and fences

May 16th, 2023 No comments

Fenced areas are often illustrative of the role of herbivores in shaping vegetation [1]. Here is an example from Schönbuch Nature Park (south west of Stuttgart, Germany), where you can see how the vegetation is shaped by different densities of red deer (Cervus elaphus). Is this park-like landscape (Fig. 2; inside the enclosure) an example of the prehistoric lowland landscapes in Central Europe?

Fig. 1. Fence separating the area with absence (left) / presence (right) of red deer
Fig. 2. Within the enclosure where the density of red deer is highest. Is this park-like landscape an example of the prehistoric lowland landscapes in Central Europe?
Fig. 3. Hervivores of central Europe, from [2].

References
[1] Pausas JG & Bond WJ. 2020. Alternative biome states in terrestrial ecosystems. Trends Pl Sci, 25(3), 250–263. [doi | pdf

[2] Vera FWM. 2000. Grazing ecology and forest history. CAB International.

Postfire flowering: Narcissus assoanus

March 23rd, 2023 No comments

Spectacular postfire flowering of Narcissus assoanus 7 month after fire (Costur 8/2022, Castelló, E Spain).

More on: postfire flowering | Narcissus | regeneration | resprouting | fire ecology 

Seed dormancy: a glossary

February 1st, 2023 No comments

We have recently reviewed concepts related to seed dormancy and the mechanism of dormancy release (see references 1, 2, 3 below). Here we summarize the main definitions considered.

Seed dormancy: delayed germination even when conditions are favorable. It is a state of metabolic inactivity in the seed that prevents the embryo from growing and thus the seed from germinating. There are two major classes of seed dormancy, inherent dormancy and imposed dormancy.

  • Inherent (or innate) dormancy: dormancy is an internal response through retarded embryo maturity or metabolic inactivity. This is often called just ‘dormancy’; it has also been called primary dormancy, but this name is not appropriate (see Secondary dormancy below). There are three basic types of inherent dormancy, depending on the mechanism of release: morphological, physical and physiological dormancy. Some seeds may have multiple mechanisms where they combine physiological and either morphological or physical dormancy.
    • Physical dormancy (PY): a type of inherent dormancy where the seed coat is impermeable to water and/or oxygen such that metabolism cannot occur and the seed cannot germinate even if hydrothermal conditions are suitable. Physical dormancy is typically released by heat, or by physical or chemical scarification: 
        • Heat-released dormancy: seeds require a heat pulse for breaking physical dormancy that exceeds soil temperatures experienced during summer and is comparable with fire heat.
        • Scarification-released dormancy: seeds require a physical or chemical scarification (different from heat) for breaking physical dormancy (e.g., scratching the surface of the seed coat). Scarification may be a convenient tool for breaking dormancy in horticulture, but its ecological role in the soil is not well known; it may be related to seed coat decays over time through temperature fluctuations or microbial processes. Scarification-released dormancy also occurs in species that do not form a seed bank: seeds of fleshy-fruited species are typically dormant, and scarification (chemical or mechanical) through the guts of frugivorous vertebrates releases their dormancy; in that case, dormancy is a strategy for long distance dispersal [2].
    • Physiological dormancy (PD): a type of inherent dormancy in which metabolic requirements have yet to be met and germination cannot proceed even if hydrothermal conditions are suitable. Some examples of physiological dormancy are:
        • Smoke-released dormancy: a type of physiological dormancy that is maintained until chemical byproducts in smoke or ash from the combustion of plant matter (collectively termed ‘smoke’) breaks dormancy by catalysing production of enzymes required for initiating metabolic activity and germination.
        • Inhibitor-released dormancy: a type of physiological dormancy where chemical inhibitors must be removed to allow germination. It has been observed in some seeds that germinate only when removed from the fruit, or in mistletoes, when the mucilage is removed (by frugivorous birds). [3].
        • Cold-released dormancy: a type of physiological dormancy that is maintained until the seed is exposed to periods of cold (e.g., ~5°C for two months) that promotes production of cofactors required for initiating metabolic activity [3].
        • Light/dark-released dormancy: a type of physiological dormancy that is maintained until the seed is exposed to periods light-dark that promotes production of specific cofactors required for initiating metabolic activity (photoperiod-controlled dormancy or photodormancy).
    • Morphological dormancy (MD): Dormancy is maintained in an underdeveloped embryo which requires a period of post-dispersal maturation (after-ripening) before the seed is ready to germinate. Morphological dormancy due to immature embryos is neither environmentally controlled nor metabolically inactive and might be better considered as post-release embryo maturation and only apparently dormant (pseudodormancy) [3].
  • Imposed dormancy: environmentally-imposed dormancy is the state where metabolic activity continues to be suppressed as external conditions remain unsuitable for germination. Some times it is called secondary dormancy but this term is inappropriate because it may be the only form of dormancy among many seeds, so it cannot be considered secondary in a temporal sense nor minor in a functional sense [3]. In species with heat-released dormancy, this state is maintained between the fire event and the first substantial postfire rains but may be minimal among smoke-responsive seeds if the chemicals are only absorbed once the seeds have imbibed. [1,3]

Dormancy syndrome: A correlated suite of traits that is coordinated to maintain seed dormancy during storage, execute seed dormancy release in response to a specified stimulus, and respond quickly to favorable germination conditions when they become available [1]. In fire-prone ecosystems, we defined four dormancy syndromes: Heat-released dormancy, Smoke-released dormancy, Non-fire-released dormancy, Non-dormancy [1]. Fire-released dormancy is a concise term for heat-released and smoke-released dormancy syndromes [1]

Heat-stimulated germination: Heat per se does not stimulate germination but breaks dormancy that allows germination to proceed later, i.e. once suitable hydrothermal conditions are met. Thus, this term refers to the heat-released dormancy syndrome [1].

Secondary dormancy: under some conditions seeds may return to a dormant state following the introduction of earlier or new inhibitory conditions that re-impose seed dormancy. Dormancy cycling may occur when seeds that have previously broken inherent or imposed dormancy return several times to that state (secondary inherent or imposed dormancy) following conditions that annul the current dormancy-release state.

Smoke-stimulated germination: In physiologically dormant seeds, specific smoke chemicals break dormancy and allow germination to proceed. These chemicals may be absorbed by dry seeds but, once the wet season begins, they are more likely to be absorbed dissolved in the soil solution during imbibition so that germination proceeds without further delay. Thus, this term is equivalent to the smoke-released dormancy syndrome [1]. Smoke chemicals may also hasten the rate of germination of non-dormant seeds among some species.

Dormancy-released pathways:  There are at least three ways by which seeds release dormancy [3]:

  • Pathway 1 (inherent/imposed dormancy release pathway): First inherent dormancy is broken, but for germination to proceed, imposed dormancy must also be broken at some later stage, that is, when suitable hydrothermal conditions prevail. E.g., the heat of a fire may break (inherent) physical dormancy, but seeds will not germinate until the first significant rainfall events (breaking environmental imposed dormancy).
  • Pathway 2 (imposed dormancy release pathway): seeds that lack inherent dormancy (non-dormant) may still encounter an environment that does not meet their germination requirements, so that they remain under imposed dormancy until the appropriate hydrothermal conditions are met.
  • Pathway 3 (imposed/inherent dormancy release pathway): first imposed dormancy is broken before inherent (physiological) dormancy release is possible. Some seeds must already be imbibed before the inherent physiological dormancy is released, e.g, before the seed is receptive to light/dark or to cold that breaks inherent dormancy (light/dark-dormancy release or cold-dormancy release).

Bet-hedging vs best-bet strategies: In unpredictable arid ecosystems, seed dormancy is a bet-hedging strategy, as it favours spreading the risk of recruitment failure over many years. In seasonal environments where fires are predictable, seed dormancy is a best-bet strategy as seed dormancy maximizes germination in a single year when conditions are optimal, following the first substantial rains after fire [2] (this best-bet strategy is also termed environmental matching [1]). Serotiny (seeds stored in the canopy seed bank with delayed seed release and dispersal [link]) is usually not considered within the concept of dormancy, but it certainly fits the best-bet strategy [2].

References

[1] Pausas JG. & Lamont BB. 2022. Fire-released seed dormancy – a global synthesis. Biol. Rev. 97: 1612-1639. [doi | pdf | supp. mat. | data (figshare)] (highlighted in plant.org)

[2] Pausas JG, Lamont BB, Keeley JE., Bond, WJ. 2022. Bet-hedging and best-bet strategies shape seed dormancy. New Phytol. 236: 1232-1236. [doi | wiley | pdf]

[3] Lamont BB & Pausas JG 2023. Seed dormancy revisited: dormancy-release pathways and environmental interactions. Funct. Ecol. [doi | pdf | data: dryad | plain language summary]

 

Lizards hear wildfires

January 9th, 2023 No comments

In 2021 we described that some lizards can detect wildfires by smelling the smoke, and in this way they can react quickly, e.g., by moving to a safe place [1]. Specifically we performed that study with the mediterranean lizard Psammodromus algirus, from eastern Spain. In a recent paper, we suggest that some lizards are able to recognise wildfires by their sound! [2]. This study was performed with another mediterranean lizard, Sceloporus occidentalis (western fence lizard), from southern California.

Western fence lizard (Sceloporus occidentalis), from southern California.. Photo: L. Álvarez-Ruiz

References

[1] Álvarez-Ruiz L, Belliure J, Pausas JG. 2021. Fire-driven behavioral response to smoke in a Mediterranean lizard. Behavioral Ecology 32: 662–667. [doi | oup | data:dryadpdf] – blog

[2] Álvarez-Ruiz L, Pausas JG, Blumstein DT, Putmanb BJ. 2023. Lizards’ response to the sound of fire is modified by fire history. Animal Behaviour 196: 91–102. [doi | sciencedirect | pdf]

More on: fire & lizards  and  fire & fauna

Fire increases precocity in pines

December 24th, 2022 No comments

Fires are a natural disturbance in many ecosystems. Consequently, plant species have acquired traits that allow them to resist and regenerate in an environment with recurrent fires [1]. A key trait in fire-prone ecosystems is the age at first reproduction (maturity age); populations of non-resprouting species cannot persist when the fire interval is shorter than this age. Maturity age is variable among individuals (Fig. 1), so we hypothesized that short fire intervals select for early seed production (precocity) [2]. We evaluated the age at first reproduction in Pinus halepensis (a non-resprouting serotinous pine species) in eastern Iberia (Fig. 2, for a difficult example; [2]). Our results show (Fig. 3) a selection towards higher precocity in populations subject to higher fire frequency (shorter fire intervals). Due to this higher precocity, pines stored more cones and therefore, increased their potential for reproduction post-fire. We provide the first field evidence that fire can act as a driver of precocity. Being precocious in fire-prone environments is adaptive because it increases the probability of having a significant seed bank when the next fire arrives.

Fig. 1. A 12-year-old trees that is immature (A) and another of the same age that started reproduction at 9 years old (B; the zoom shows pine cones of the different yearly cohorts). Pinus halepensis, from [2]
Fig. 2. Mediterranean pines may produce more than one whorl per year. The pictures show an upper branch (A), the upper part of the trunk (B), and the lower part of the trunk (C) of Pinus halepensis. Blue arrows indicate the first whorl of a growing season (starting from the bottom); red arrows, the second whorl of the same year; and green arrows a third whorl. Note that the second and third whorls normally have fewer and thinner branches per whorl and/or are close to the other whorls from the same growing season. From [2]
Fig. 3: Probability of reaching sexual maturity (precocity) against the age (in years) of the tree (Pinus halepensis) for areas with high frequency of crown fires (in red, upper line) and areas with low frequency of crown fires (in blue; lower lines). From [2].

References

[1] Keeley JE & Pausas JG. 2022. Evolutionary ecology of fire. Ann. Rev. Ecol. Evol. Syst. 53: 203-225. [doi |eprint | pdf]

[2] Guiote C & Pausas JG. 2023. Fire favors sexual precocity in a Mediterranean pine. Oikos [doi | pdf]

Evolutionary Ecology of Fire

November 4th, 2022 1 comment

Fire is an evolutionary pressure that shaped our biodiversity [1,2]. In a recent paper we summarized the current state of the art in this topic [3]. Fire has been an ecosystem process since plants colonized land over 400 million years ago [1]. Many diverse traits provide a fitness benefit following fires, and these adaptive traits vary with the fire regime [4]. Some of these traits enhance fire survival, while others promote recruitment in the postfire environment. Demonstrating that these traits are fire adaptations is challenging, since many arose early in the paleontological record, although increasingly better fossil records and phylogenetic analysis (figure below) make timing of these trait origins to fire more certain. Resprouting from the base of stems is the most widely distributed fire-adaptive trait, and it is likely to have evolved under a diversity of disturbance types. The origins of other traits like epicormic resprouting [5], lignotubers [6], serotiny [7], thick bark [8], fire-stimulated germination [9], and postfire flowering are more tightly linked to fire. Fire-adaptive traits occur in many environments: boreal and temperate forests, Mediterranean-type climate (MTC) shrublands, savannas, and grasslands. MTC ecosystems are distinct in that many taxa in different regions have lost the resprouting ability and depend solely on postfire recruitment for postfire recovery [10]. Overall, evolutionary fire ecology not only provides an understanding of the origin and history of our biota, it also sets the basis for the management of our ecosystems in a world undergoing fire-regime changes.

Time of origin (x-axis) of five different fire traits (different colors) for different lineages (y-axis) estimated from dated phylogenies. Bars expand the uncertainty of the time of origin (e.g., stem versus crown age). From [3]

References

[1] Pausas JG & Keeley JE 2009. A burning story: The role of fire in the history of life. BioScience 59: 593-601 [doiOUP | pdf | post]

[2] He T, Lamont NB, Pausas JG 2019. Fire as s key driver of Earth’s biodiversity. Biol. Rev. 94:1983-2010. [doi | pdf

[3] Keeley JE & Pausas JG 2022. Evolutionary ecology of fire. Ann. Rev. Ecol. Evol. Syst. 53: 203-225. [doi | pdf] <- New paper

[4] Keeley JE, Pausas JG, Rundel PW, Bond WJ, Bradstock RA 2011. Fire as an evolutionary pressure shaping plant traits. Trends Pl. Sci. 16: 406-411. [doi | sciencedirect | trends | pdf | For managers]

[5] Pausas J.G. & Keeley J.E. 2017. Epicormic resprouting in fire-prone ecosystems. Trends Pl. Sci. 22: 1008-1015. [doi | sciencedirect | pdf] [post | Cover image]

[6] Pausas JG, Lamont BB, Paula S, Appezzato-da-Glória B & Fidelis A 2018. Unearthing belowground bud banks in fire-prone ecosystems. New Phyt. 217: 1435–1448. [doi | pdf | suppl. | BBB database]

[7] Lamont BB, Pausas JG, He T, Witkowski, ETF, Hanley ME. 2020. Fire as a selective agent for both serotiny and nonserotiny over space and time. Crit. Rev. Pl. Sci. 39:140-172. [doi | pdf | suppl.]

[8] Pausas JG 2015. Bark thickness and fire regime. Funct. Ecol. 29:317-327. [doi | pdf | suppl.] & Pausas JG 2017. Bark thickness and fire regime: another twist. New Phytol. 213: 13-15. [doi | wiley | pdf]

[9] Pausas JG & Lamont BB 2022. Fire-released seed dormancy – a global synthesis. Biol. Rev. 97: 1612-1639. [doi | pdf | supp. mat.]

[10] Pausas JG & Keeley JE 2014. Evolutionary ecology of resprouting and seeding in fire-prone ecosystems. New Phyt. 204: 55-65. [doi | wiley | pdf]

Alternative Biome States in Brazil

October 31st, 2022 No comments

I have recently been in Minas Gerais, Brazil (in the Cerrado region). I visited different biomes (forests, savannas, grasslands) occurring in the same climate, i.e., Alternative Biome States [1,2]. The sharp boundaries that separate the different biomes (photos blow) suggesting the existence of strong feedbacks [3]. Savannas and grasslands are maintained by frequent fires (flammable or pyrophilic communities) in climates where dense forest can occur; frequent fires maintain those open ecosystems dominated by light-demanding grasses, and woody plants with traits for fire survival (thick corky bark [4], epicormic resprouting [5], belowground organs [6]). In contrast, forest rarely get burn (non-flammable or pyrofobic communities), as the low light inhibit grasses and generate microclimatic conditions that are not favorable for fire (no grasses, high humidity, low wind, etc.) but favorable for shade-tolerant forest trees.

Forest-grassland mosaic in Serra da Canastra, Minas Gerais, Brazil
Forest-grassland mosaic in Serra da Canastra, Minas Gerais, Brazil
Savanna dominated by Vochysia thyrsoidea (Vochysiaceae; the large tree), in Serra da Canastra, Minas Gerais, Brazil. Brazilian savannas are often termed “cerrado”.

References

[1] Pausas JG & Bond WJ. 2020. Alternative biome states in terrestrial ecosystems. Trends Pl Sci 25: 250-263. [doi | sciencedirect | cell | pdf]

[2] Dantas VL, Hirota M, Oliveira RS, Pausas JG. 2016. Disturbance maintains alternative biome states. Ecol Lett 19: 12-19. [doi | wiley | pdf | supp.]

[3] Pausas JG & Bond WJ. 2022. Feedbacks in ecology and evolution. Trends Ecol Evol 37: 637-644. [doi | sciencedirect | pdf]

[4] Pausas JG. 2017. Bark thickness and fire regime: another twist. New Phytol 213: 13-15. [doi | wiley | pdf]

[5] Pausas JG & Keeley JE. 2017. Epicormic resprouting in fire-prone ecosystems. Trends Pl Sci 22: 1008-1015. [doi | sciencedirect | pdf

[6] Pausas JG, Lamont BB, Paula S, Appezzato-da-Glória B & Fidelis A. 2018. Unearthing belowground bud banks in fire-prone ecosystems. New Phytol 217: 1435–1448. [doi | pdf | suppl. | BBB database]

Fire response of Bonelli’s eagle

September 30th, 2022 No comments

There is still little information on the response of many animals to fire [1, 2], and this limited knowledge is even more important for large predators (e.g. raptors) as their behavior in relation to fire are not easy to observe. We studied the fire response to a Bonelli’s eagle (Aquila fasciata) thanks to a serendipity event: a wildfire (Artana fire; eastern Spain) occurred in an area where friends of mine had an eagle being tracked by a GPS/GMS [3]. This allowed us to follow their behavior during the fire, compare it with both before and after the fire (during two years), and with other neighbor eagles that were also being tracked [3].

The results suggest that despite the fire affected most of the eagle’s core home-range, including the nest site, its activity was hardly affected by the fire. During the fire, the eagle moved away from the fire but did not leave its home-range; she was back to the center of the home-range when the fire was still burning (at low intensity). The minor movements during the fire were probably due to the smoke or/and to the firefighters activity (which include planes). And during the two following years, the behavior of the eagle was similar the behavior when the landscape was not burned. This suggest that the eagles prey (rabbits, pigeons, small mammals) were also little affected by the fire.

An animations of the movements of the eagle in relation to the home-range and the burned area is available here.  

Bonelli’s eagle (Aquila fasciata) feeding in the Artana burned area (eastern Spain). Photo: Pascual López

References

[1] Pausas J.G., Parr C.L. 2018. Towards an understanding of the evolutionary role of fire in animals. Evol. Ecol. 32: 113–125. [doi | pdf]

[2] Pausas J.G. 2019. Generalized fire response strategies in plants and animals. Oikos 128: 147-153 [doi | pdf | blog1 blog2 blog3 | cover image]

[3] Morollón S. Pausas J.G., Urios V., López-López P. 2022. Wildfire response of GPS-tracked Bonelli’s eagles in eastern Spain. Int. J. Wildland Fire 31: 901-908 [ doi | ijwf | pdf | animation]

Incendis forestals: carta al poble valencià

September 10th, 2022 No comments

Este text el vaig escriure a l’agost, de vacances, quan encara estaven cremant els incendis de Vall d’Ebo i Bejis, i se va publicar al diari Levante-ENV el dia 9 de septembre de 2022

Enguany els incendis forestals han cremat de nou una part important de les nostres muntanyes. Al menys de moment, no ha sigut tant greu com el fatídic 1994, ni com el 2012, però suficient per a commoure a part de la societat valenciana, i en especial a les persones que viuen a la Marina Alta, l’Alto Palancia, i comarques veïnes. La vegetació mediterrània se regenerarà de la mateixa manera que ho ha fet les altres vegades, els agricultors afectats patiran un nova crisi existencial, i l’estructura del paisatge quedarà marcada durant unes quantes dècades. Els efectes concrets sobre la biodiversitat s’hauran d’estudiar amb detall.

La primera reacció ha sigut la de buscar culpables, sovint de manera simplista. El problema dels grans incendis és complexe, i no té un únic determinant. Els grans incendis es produeixen quan coincideixen una sèrie de factors: ignicions (antròpiques o llamps) en una zona amb vegetació contínua i fàcilment inflamable, en una època seca (estiu), i en condicions meteorològiques adverses (ones de calor, fort vent). Cap d’estos factors per si sols genera grans incendis; és la simultaneïtat d’aquests factors la que fa que els incendis siguen grans i intensos (megaincendis).

Gran part de la nostra vegetació natural és inflamable (per exemple els matollars i boscos mediterranis de pi blanc) i cada any tenim una estació càlida i seca (estiu), per tant vivim en una zona naturalment propensa a incendis. A més, al nostre territori plou suficient com per a tenir vegetació densa i contínua. En el passat (durant gran part del segle XX), la vegetació no era tan densa i estava bastant fragmentada perquè teníem un paisatge rural, amb moltes zones dedicades a l’agricultura i pastures (a voltes sobrepasturades), que alternaven amb boscos on se feia llenya. En estes condicions els incendis eren xicotets i fàcils d’apagar. La industrialització va fer que el món rural s’anés abandonant, i el que eren camps de cultius i pastures s’han anat colonitzant de vegetació típica de les primeres etapes de successió. Aquesta colonització de camps abandonats, junt amb les grans plantacions forestals (no gestionades apropiadament), ha fet que augmenti molt la continuïtat de la vegetació. Per tant, quan hi ha un incendi, se propaga molt més fàcilment i se poden generar incendis molt extensos. L’abandonament rural no és una cosa d’ara, és producte de les polítiques fetes durant les darreres dècades en que no s’ha fet cap esforç per conservar el nostre món rural mentre s’estimulaven (econòmicament) els centres urbans i el turisme. Ara, aquest abandonament del món rural és difícil de revertir, poca gent vol tornar a la vida rural; com a mínim hem de procurar no perdre el món rural que queda i estimular el seu increment. Un dels punts claus per reduir l’abandonament rural és que la gent dedicada a l’agricultura i ramaderia tinguen compradors dels seus productes. Les persones que consumeixen prioritàriament productes de grans superfícies sense fixar-se en l’origen del producte possiblement estan contribuint a l’abandonament rural (i als incendis forestals). La gestió forestal pot intentar recrear algunes de les discontinuïtats mitjançant tallafocs, aclarides, i cremes prescrites, però difícilment pot actuar en tota la massa forestal del territori, que segueix creixen com a conseqüència de l’abandonament.

Però la vegetació densa i continua per si sola no genera incendis. Se necessiten ignicions, que poden ser antròpiques, però com hem vist enguany, també poden ser llamps (en el cas dels incendis de la Vall d’Ebo, Bejís i Olocau). A més, se necessiten també condicions meteorològiques que facilitin la propagació del foc (vent i onades de calor). No és necessari dir que entre tots hem canviat el clima (mitjançant l’emissió de gasos d’efecte hivernacle) de manera que hem incrementat la freqüència i intensitat de les onades de calor. Un cop hem canviat el clima, és esperable que hi haja un increment en la mortalitat dels arbres per sequera, així com un increment de la probabilitat d’incendis. Seria il·lús voler conservar la vegetació del segle XX amb el clima del XXI. La nostra vegetació i les tècniques de gestió del paisatge teníen una certa lògica amb el clima del segle passat, però no s’ajusten bé al nou clima del segle XXI, que seguim canviant. Els grans incendis que se donen a molts llocs del món són un símptoma d’aquest desajust.

Hem d’exigir polítiques clares i dirigides a ajudar i estimular el món rural, a gestionar de manera sostenible els nostres paisatges, i a reduir el canvi climàtic. Els incendis no se poden eliminar totalment dels nostres paisatges mediterranis, si es que volem conservar la biodiversitat, però la gestió hauria de fer que foren incendis més xicotets i més sostenibles. Per exemple, un incendi de 1000 ha cada any és més sostenible que un incendi de 10,000 ha cada 10 anys. Però a més de les polítiques de gestió, és important tenir en compte que sense la participació de tota la societat, la tasca serà molt difícil. Tots tenim una part de responsabilitat en els productes i l’energia que consumim, i en els gasos d’efecte hivernacle que emetem. I la nostra responsabilitat en les emissions no és només deguda al nostre propi transport (cotxe, viatges de turisme), sinó que també al transport de les mercaderies que consumim, i les infraestructures que utilitzem. Hem de repensar unes quantes coses del nostre comportament si volem seguir mantenint bona qualitat de vida en el clima que hem generat per aquest segle XXI.

Seed dormancy, bet-hedging, and best-bet

September 2nd, 2022 No comments

Seed dormancy is a key plant characteristic that occurs among many species worldwide. One mechanism that select for seed dormancy is the bet-hedging strategy. In unpredictable environment (i.e., with high interannual variability) there is a benefit in spreading the germination over a number of years to reduce year-to-year variation in fitness but taking advantage of exceptionally good years for establishment. In those environments, seed dormancy is adaptive; each year there is a small fraction of the seed crop that germinates and the other seeds remain dormant in the soil. Because the environmental conditions of most years are poor, successful establishment only occurs in good (wet) years. Thus bet-hedging selects for seed dormancy and it is a mechanism for living in highly unpredictable environments such as arid ecosystems [1]

There is another environmental setting that also selects for seed dormancy: seasonal (predictable) climate with a dry season during which the vegetation is highly flammable and thus wildfires are frequent (e.g., mediterranean, savanna, warm temperate, and dry boreal ecosystems). In those ecosystems, seed dormancy is adaptive and fire provide both a mechanism for dormancy release (proximate cause) and conditions (postfire) optimal for germination and establishment (low competition, high resource availability, low predation, low pathogen load) that increase fitness and allow maintenance of the population (ultimate cause) [1,2]. Dormant seeds survive the passage of fire and the heat or the chemicals from the combustion (collectively called ‘smoke’ [2,3]) are the stimulus for the seed to recognize a fire gap to germinate. That is, postfire recruitment occurs in a single pulse after fire. Here selection does not favor spreading the risk of recruitment failure over many years (as in the bet-hedging strategy) but, instead, maximizes germination in a single year when conditions are optimal, after fire. We call this strategy the best-bet strategy [1] or environmental matching [2]. This strategy selects for seed dormancy to accumulates seeds in the soil seedbank but also selects for serotiny to accumulate seeds in the canopy seedbank [4]; in both cases, species recruit mostly after fire and not during the interfire period.

There is a further driver that selects for seed dormancy but it does not imply the formation of seed banks (in contrast with bet-hedging and best-bet). Many seeds have acquired seed dormancy to facilitate long-distance dispersal. The clearest example is dispersal by vertebrate frugivores (endozoochory). Frugivores consume the fruit pulp and defaecate or regurgitate the seeds far from the mother plant. This means that seeds need to resist passage through the gut and remain intact until arriving at a new microsite for germination. Thus, seeds of fleshy fruited species typically are dormant, and scarification through the gut releases their dormancy. While bet-hedging spreads germination of seeds over time, this strategy spread the seeds across the space and thus it could be viewed as a spatial bet-hedging strategy.

Figure: Schematic representation of the dynamics of seed recruitment for plants lacking seed dormancy (nondormant; top panel), and for plants with dormant seeds following the bet-hedging strategy (middle panel) and the best-bet strategy (bottom panel). The figure shows the moment of flowering (red asterisk; spring), the germination (black bars; autumn), the seed bank in autumn (empty bars), the recruitment 2 months later (green bars) and the fire (flame; summer). As an example, the seasons are considered as in the Northern Hemisphere, and vertical dotted lines are the end of the year. From [1]
Table: Main characteristics of the evolutionary strategies that select for seed dormancy and seed banks (bet-hedging, best-bet), together with the nondormant strategy.

References

[1] Pausas JG, Lamont BB, Keeley JE., Bond WJ. 2022. Bet-hedging and best-bet strategies shape seed dormancy. New Phytol. [ doi | wiley | pdf]

[2] Pausas JG. & Lamont BB. 2022. Fire-released seed dormancy – a global synthesis. Biol. Rev. 97: 1612-1639. [doi | pdf | supp. mat. | data (figshare)

[3] Keeley JE & Pausas JG. 2018. Evolution of ‘smoke’ induced seed germination in pyroendemic plants. South African J. Bot. 115: 251-255. [doi | pdf]  

[4] Lamont BB, Pausas JG, He T, Witkowski, ETF, Hanley ME. 2020. Fire as a selective agent for both serotiny and nonserotiny over space and time. Critical Rev. Pl. Sci. 39:140-172. [doi | pdf | suppl.]

Beneficios de no cortar los árboles después de un incendio

September 1st, 2022 No comments

Este artículo, ligeramente modificado, se publicó en The Conversation (5-9-2022), y se tradujó al inglés en Mednigth (7-9-2022)

Este verano Europa ha sufrido un número importante de grandes incendios. Los ingredientes principales que han convertido igniciones, tanto antrópicas como por rayos, en grandes incendios han sido la gran densidad y continuidad de la vegetación (producto del abandono rural y de las grandes plantaciones mal gestionadas) y las largas e intensas olas de calor (producto de nuestra inacción climática).

Después de un incendio en un bosque, una pregunta recurrente es: ¿qué es mejor, cortar los árboles muertos o dejarlos en pie?

Evidentemente, la gestión posterior al incendio dependerá del objetivo. No se gestionarán de la misma manera plantaciones o bosques productivos donde se quiere aprovechar económicamente la madera (aunque la madera quemada suele tener poco valor económico), que bosques donde se quiere maximizar la conservación de la biodiversidad y la regeneración del ecosistema (los árboles quemados sí tienen valor ecológico).

Desde el punto de vista ecológico, cortar los árboles y extraer la madera quemada constituye una perturbación después de otra perturbación (es decir, una perturbación compuesta) y puede tener consecuencias negativas para la biodiversidad y la regeneración del ecosistema (por ejemplo: enlace, enlace, enlace).

Aquí se listan algunos de los posibles beneficios para el ecosistema y la biodiversidad de dejar en pie los árboles muertos en un bosque que ha sufrido un incendio reciente. Evidentemente, cada bosque quemado es diferente, y el papel relativo de cada uno de estos beneficios puede variar de un lugar a otro dependiendo de muchos factores (severidad del fuego, tipo de vegetación, edad, densidad, posición topográfica, historia previa, etc.). Pero, en cualquier caso, se deberían considerar estos potenciales beneficios antes de decidir cortar los árboles:

  1. Fuente de alimento: Los árboles muertos son alimento y hábitat de una gran diversidad de hongos e insectos (xilófagos y saprófitos), que a su vez son alimento de otros animales como las aves. Por lo tanto, mantienen una red trófica que ayuda a la regeneración del ecosistema. Cabe recordar que los escolítidos, unos pequeños escarabajos que pueden generan plagas en coníferas, no se alimentan de árboles muertos.
  2. Fuente de materia orgánica: Los árboles muertos son una fuente de materia orgánica y nutrientes necesaria para el reciclado de los ecosistemas (los ciclos biogeoquímicos). Su extracción supone una pérdida de fertilidad para el ecosistema (ejemplos: enlace1, enlace2, enlace3).
  3. Refugio y dipersión de semillas: Muchos animales forestales utilizan los bosques quemados, incluidos pequeños vertebrados que encuentran cierta protección frente a la depredación por rapaces. Algunos vertebrados ayudan directamente a la regeneración de la vegetación. Por ejemplo, muchas aves frugívoras defecan semillas mientras se posan en árboles quemados (efecto percha), contribuyendo así a la dispersión de semillas y la regeneración de la zona incendiada. Otro ejemplo lo constituyen los arrendajos, que utilizan bosques quemados (y no los matorrales o bosques cortados) para esconder bellotas. Por eso son clave para el incremento de las quercíneas (carrascas, robles y alcornoques). Al ser estas especies rebrotadoras, aumentan la resiliencia de los ecosistemas.
  4. Protección frente a la erosión: Las copas de los árboles quemados disminuyen el impacto de las gotas de lluvia en el suelo y, por lo tanto, disminuyen el potencial de erosión posincendio.
  5. Aportan humedad: Los bosques quemados pueden retener nieblas y, por lo tanto, mantener mayor humedad en el ecosistema, contribuyendo así a una mejor regeneración.
  6. Reducción de la intervención humana: Mantener un bosque quemado evita la entrada de maquinaria pesada y el arrastre de troncos. Estas acciones pueden tener un efecto negativo en el suelo y en la regeneración incipiente, incluso pueden generar inicios de cárcavas.
  7. Ahorro: Mantener un bosque quemado también reduce el gasto económico, que se puede utilizar para otras tareas de restauración y monitorización de la regeneración.
Marcas dejadas por los picapinos en un tronco quemado. Guadalajara 2016

En general, dejar en pie los árboles en un bosque quemado permite mantener un ambiente semiforestal beneficioso para la regeneración y el funcionamiento del ecosistema forestal. Por el contrario, la corta de los árboles muertos beneficia a especies de matorrales y ecosistemas abiertos.

Alternativas intermedias. Una solución que a menudo se ha propuesto es la de cortar los árboles y extraer la madera, pero dejando un porcentaje de árboles en pie. Esta solución permite mantener algo de madera muerta que puede beneficiar a algunos insectos y al reciclado de cierta cantidad de materia orgánica y nutrientes (típicamente un porcentaje bajo). Pero como se suele dejar una densidad baja de árboles en pie, tendrán más riesgo de ser derribados por el primer vendaval o nevada. Otra solución es cortar pero no extraer la madera (o al menos dejar el ramaje), de manera que se mantienen intactos algunos beneficios (materia orgánica y nutrientes, y la reducción de la erosión). En ambas alternativas normalmente se pierde el ambiente semiforestal de un bosque quemado y, por lo tanto, también se pierden muchos otros de los beneficios arriba mencionados.

¿Pueden favorecer otros incendios? A veces, la razón por la que se cortan y extraen los árboles muertos es la de disminuir la biomasa seca que podría ejercer de combustible en un segundo incendio. Pero este incremento de la probabilidad de un segundo incendio es a menudo incierto, especialmente porque justo después del incendio no hay suficiente biomasa fina para otro fuego. Y al cabo de unos pocos años, el matorral o bosque joven podría ser ya muy inflamable siendo la contribución relativa de los árboles muertos relativamente poco importante. Una solución es cortar y extraer un porcentaje de los árboles muertos después de al menos un año o más del incendio. Se enfocaría en zonas donde la regeneración ya está asegurada. Esto puede reducir el impacto negativo de la corta.

Árboles quemados para retener el suelo. En un incendio a menudo se pueden observar zonas concretas donde la probabilidad de pérdida de suelo será elevada (por ejemplo, debido a las altas pendientes, suelo arenoso, vegetación preincendio muy pobre, etc.). Como la pérdida de suelo es lo peor que puede ocurrir después de un incendio (el suelo tarda muchísimo en regenerarse), en estas áreas se requieren actuaciones urgentes para evitarlo. En estos casos, parece justificado cortar árboles quemados y utilizarlos para retener el suelo. Se pueden utilizar las ramas, los troncos en fajinas o hacer pequeños diques de contención. Pero se debe evitar generalizar estas actuaciones a toda la zona quemada si no es realmente necesario. Por ejemplo, no tiene sentido realizarlas en zonas con poca pendiente, en suelos muy pedregosos, en zonas con bancales bien conservados, o en zonas con abundantes plantas rebrotadoras.

 

Valorar las consecuencias: Vivimos en un entorno con vegetación inflamable y un paisaje y un clima cada vez más propensos a incendios debido a la acción humana. Para mejorar nuestra convivencia con el fuego, es importante mejorar al máximo la gestión posincendio. El gestor debe balancear los criterios socioeconómicos y ecológicos antes de realizar cualquier acción. Y sea cual sea la decisión, sería deseable evaluar el posible impacto del tipo de intervención seleccionado y, si es necesario, rectificar en la medida de lo posible.

Incendios, clima y paisaje, o de cómo adaptarnos a la nueva realidad

August 1st, 2022 No comments

Una versión un poco simplificada de este texto se publicó en TheConversation (18/7/2022), en elDiario.es (19/7/2022), en elPeriodico (2/8/2022), entre otros periódicos, bajo el título “Cómo adaptarnos a la nueva realidad de incendios”. También se ha publicado en inglés en Mednight (3/8/2022): “Adapting to the new reality of fires”, y en portugués en Esquerda (4/8/2022): “Como nos podemos adaptar à nova realidade dos incêndios”.

Hace 40 millones de años, la Antártida estaba cubierta de grandes bosques. Y hace 25 000 años, media Europa estaba cubierta de hielo y la otra media eran estepas frías. Gracias a la paleontología hoy sabemos que la vegetación de todo el mundo ha ido cambiando según han ido sucediendo cambios climáticos. La vegetación y el clima están ligados, ya lo decía Humboldt (1769–1859), y es una de las primeras lecciones de ecología.

Si ahora, con nuestra inacción climática (fig. 1), hemos aceptado que cambie el clima, debemos aceptar también que cambie la vegetación. Es iluso querer conservar la vegetación del siglo XX con el clima del siglo XXI. Igualmente, la gestión forestal del siglo XXI no puede ser como la del siglo XX, cuando el clima era menos árido.

Fig. 1. Inacción climática. Concentración de CO₂ en la atmósfera (en ppm) a lo largo de los años (de 1960 a 2020). En colores se muestra el incremento de temperaturas a escala global (climate stripes). También se indican las diferentes reuniones internacionales realizadas para debatir sobre el cambio climático, y lo poco útiles que han sido. Tadzio Mueller / Wiebke Witt / Marius Hasenheit / Sustentio, CC BY

Los grandes incendios forestales

Los grandes incendios no se producen por una sola causa (el cambio climático o las plantaciones forestales). Se producen por la coincidencia de igniciones en periodos de sequía y condiciones meteorológicas adversas (olas de calor, viento), en zonas con vegetación continua y fácilmente inflamable [1, 2]. Estas zonas a menudo son matorrales y vegetación en etapas tempranas después del abandono rural (incluidos bosques jóvenes) o plantaciones densas no gestionadas apropiadamente.

El cambio climático interviene en la ecuación [2] porque extiende la estación propensa a incendios, agudiza las sequías, incrementa la mortalidad de plantas (y la biomasa seca) e incrementa la frecuencia de condiciones meteorológicas favorables a los incendios (por ejemplo, olas de calor). Pero el gran incremento de incendios que se ha dado en la historia reciente de España ha sido independiente del cambio climático, y asociado principalmente al abandono rural [3]. La disminución de la agricultura, del pastoreo y de la recolección de madera, y la falta de gestión en plantaciones forestales, generan paisajes más continuos y homogéneos donde el fuego se propaga fácilmente. En estos paisajes, el papel relativo del clima en los incendios aumenta a medida que dejamos que avance el cambio climático [2, 3].

La vegetación que aparecerá después de sequías e incendios recurrentes será diferente a la actual, porque muchas especies pueden no estar adaptadas a esos nuevos regímenes climáticos y de incendio. Presumiblemente la nueva vegetación será menos densa y menos forestal, y con cambios en la composición de especies.

Podemos dejar que las sequías y los incendios vayan adaptando los pasajes al nuevo clima. El problema es que esos grandes incendios pueden tener consecuencias sociales y económicas. Una alternativa es adelantarse a los incendios.

 

¿Qué podemos hacer?

Para evitar esos grandes incendios que perjudican a la sociedad, debemos adaptar nuestro paisaje y nuestro comportamiento a las nuevas condiciones ambientales. Esto incluye generar paisajes que sean más resilientes al régimen climático y de incendios que viene. Para ello, podemos poner en marcha estrategias como las siguientes

1. Generar paisajes heterogéneos

Las discontinuidades en el paisaje y los mosaicos agroforestales reducen la propagación de incendios. Esto es especialmente importante en zonas cercanas a las poblaciones humanas. Hay diversas estrategias para alcanzar este objetivo, por ejemplo: potenciar (con políticas de apoyo) el mundo rural, la agricultura y el pastoreo extensivo, así como el consumo de cercanía; incrementar las poblaciones de herbívoros naturales en zonas apropiadas para ello (rewilding o resilvestración); o realizar tareas de gestión forestal específicas en zonas críticas, como generar cortafuegos, quemas y pastoreo prescritos, o tratamientos y aprovechamientos silvícolas.

Todas estas herramientas no son excluyentes; se pueden combinar según las distintas características socieoconómicas y del terreno. Ciertamente, estimular el mundo rural es fácil de decir, especialmente desde el mundo urbano. Pero en España, por ejemplo, no es evidente que haya suficiente población dispuesta a volver a la vida rural como para generar un cambio significativo en el paisaje. Quizás podría ayudar una política de inmigración que ofreciera esa posibilidad a personas que llegan en busca de condiciones mejores a las que se dan en sus países de origen.

Fig. 2. Paisaje en la zona de Gátova (Valencia) después de un incendio en el verano de 2017. Alternar cultivos en zonas de monte (mosaicos agroforestales) ayuda a frenar su propagación. Foto: Juli G. Pausas,

2. Aprender a convivir con los incendios

Eliminar los incendios de nuestros paisajes es imposible y contraproducente [4], especialmente en el marco del cambio climático. El reto de la gestión es crear condiciones que generen regímenes de incendios sostenibles tanto ecológica como socialmente.

Enfocar las políticas de gestión de incendios únicamente a la extinción puede generar incendios grandes e intensos. Es más sostenible tener muchos incendios pequeños y poco intensos, que pocos incendios de grandes dimensiones e intensos.

Para alcanzar estos objetivos se requiere profesionalizar a los actores que intervienen en la prevención y extinción de los incendios forestales. Son ellos quienes pueden generar los regímenes de incendios sostenibles, pero en muchas ocasiones trabajan en condiciones precarias.

3. Minimizar y asumir riesgos

Debemos evitar construir viviendas e infraestructuras en zonas con bosque mediterráneo altamente inflamable y reducir al máximo la interfaz urbano-forestal. Esto no solo reduce el peligro para las personas e infraestructuras, también reduce las igniciones. Entre los mecanismos para conseguirlo se incluyen la recalificación de terrenos (a no urbanizables o incluso a agrícola) y la implementación de tasas (disuasorias) por construir en áreas con alto riesgo de incendios (pirotasas), entre otras.

En zonas ya construidas, es necesario asegurar que se realizan tareas de autoprotección, como la implementación de franjas de seguridad con poca vegetación (o con cultivos) alrededor de las viviendas, o incluso implementar sistemas de riego prescrito. Es importante asegurar que las viviendas tengan seguro contra incendios forestales, y que no esperen que los bomberos necesariamente las protejan. Hay que asumir riesgos, responsabilidades y costes si se desea vivir en medio de paisajes altamente inflamables en lugar de en una zona urbana.

Durante olas de calor, sería conveniente reducir la movilidad en el monte y en zonas de interfaz (urbano-forestal y agrícola-forestal) para minimizar el riesgo de igniciones.

Fig. 3. Ejemplo de interfaz urbano-forestal en un paisaje altamente inflamable en la Costa Brava (Platja d’Aro, Barcelona). Viviendas en una matriz forestal altamente inflamable como es este caso pronto o tarde se verán afectadas por un incendio; es cuestión de tiempo. Google Maps

4. Conservar los bosques y los humedales

Debemos conservar y restaurar los bosques en los microhábitats húmedos (refugios), para incrementar su resiliencia a los cambios en el clima.

Hay que potenciar la restauración de humedales y otros ecosistemas litorales que, aparte de los beneficios para la biodiversidad, mantienen el ciclo del agua y contribuyen a la conservación del clima [5].

La degradación de la costa (por la desecación de los humedales y la sobreurbanización) contribuye a la reducción de la precipitación [5] y al incremento de gases de efecto invernadero (vapor de agua) [5]. Potenciar vegetación en zonas urbanas (jardines, árboles en las calles) también contribuye a la conservación del clima, además de mejorar la calidad de vida de los ciudadanos (¡ninguna calle sin árboles!).

5. Restaurar con especies vegetales más resistentes

La restauración del s. XX se basaba en imitar ecosistemas del pasado. En el s. XXI, la restauración no ha de tener como referencia el pasado, sino el futuro. En proyectos de restauración y en plantaciones, se deben utilizar especies (o poblaciones de las mismas especies) más resistentes a la sequía y a los incendios que las que había con anterioridad [6]. Por ejemplo, especies y poblaciones que actualmente se encuentran en zonas más secas o con más actividad de incendios. Esto sería más sostenible que utilizar las estaciones de alta calidad forestal que se utilizaban con el clima del siglo pasado.

6. Reducir el consumo de combustibles fósiles

Esto es clave para frenar el aumento de gases de efecto invernadero, y así reducir la velocidad del cambio climático y la frecuencia de las olas de calor.

 

En conclusión

Este verano tenemos grandes incendios principalmente en el oeste del Mediterráneo, y el verano pasado los tuvimos en el este, acorde con la distribución de las olas de calor de cada año. No hay ninguna novedad ni sorpresa en ello. Hemos decidido cambiar el clima (fig. 1) y por lo tanto, la vegetación se está ajustando a ese nuevo clima. Está todo dentro de lo esperado si seguimos sin adaptar el paisaje y nuestro comportamiento a las nuevas condiciones del siglo XXI. El fuego y las sequías lo hacen por nosotros.

 

Referencias

[1] Pausas J.G. 2021. Incendios forestales: no todo es cambio climático. ; El Diario, LaMarea 19 agosto 2021 TheConversation.com (18 agosto 2021),  elDiario.es (19 agosto 2021),  laMarea.com, jgpausas.blog

[2] Pausas J.G. & Keeley J.E. 2021. Wildfires and global change. Front. Ecol. Environ. 19: 387-395. [doi | wiley | pdf | brief for managers]

[3] Pausas J.G. & Fernández-Muñoz S. 2012. Fire regime changes in the Western Mediterranean Basin: from fuel-limited to drought-driven fire regime. Climatic Change 110: 215-226. [doi | springer | pdf]

[4] Pausas J.G. 2017. Acabar con los incendios es antinatural e insostenible. 20minutos (Ciencia para llevar), 13 Julio 2017. [20minutos]

[5] Pausas J.G. & Millán M.M. 2019. Greening and browning in a climate change hotspot: the Mediterranean Basin. BioScience 96:143-151. [doi | oup | blog | pdf]

[6] Leverkus AB, Thorn S, Gustafsson L, Noss R, Müller J, Pausas JG, Lindenmayer D. 2021. Environmental policies to cope with novel disturbance regimes: steps to address a world scientists’ warning to humanity. Environ. Res. Lett. 16: 021003. [doi | pdf]

Fire regimes across the western Palearctic

July 20th, 2022 No comments

Fire regimes are shaped by climate, landscape structure, and the frequency of ignitions [1] and so globally vary across space, biogeographies, and environments. In a recent paper [3] we show how different fire regime parameters (e.g., area burnt, size, intensity, season, patchiness, pyrodiversity) varia across western Palearctic (Europe, North Africa, Near East) using remotely sensed data. We first divided the study area into eight large ecoregions based on their environment and vegetation: Mediterranean, Arid, Atlantic, Mountains, Boreal, Steppes, Continental, and Tundra. Then we characterize the fire regime for each region. The results show that the Mediterranean had the largest, most intense, and most recurrent fires, but the Steppes had the largest burnt area. Arid ecosystems had the most extended fire season, Tundra had the patchiest fires, and Boreal forests had the earliest fires of the year. The spatial variability in fire regimes was largely explained by the variability of climate and vegetation, with a tendency for greater fire activity in the warmer ecoregions. There was also a temporal tendency for fires to become larger during the last two decades, especially in Arid and Continental environments.

Figure 1. Fire size and fire intensity in eight ecoregions across western Palaearctic. From [3]
Fig. 2. Mean fire size (ha) and mean fire intensity (MW) in relation with Temperature of the driest quarter, for the eight ecoregions (colors as in Fig. 1 above). From [3].

References

[1] Pausas J.G. & Keeley J.E. 2021. Wildfires and global change. Front. Ecol. & Environ. 19: 387-395. [doi | wiley | pdf ]

[2] Pausas J.G. & Ribeiro E. 2013. The global fire-productivity relationship. Global Ecol. & Biogeogr. 22: 728-736. [doi | pdf | appendix | erratum ]

[3] Pausas J.G. 2022. Pyrogeography across the western Palearctic: a diversity of fire regimes. Global Ecol. & Biogeogr. [doi | wiley | pdf |data: dryad]

Fuego y brezales

June 30th, 2022 No comments

Video sobre la importancia del fuego en los brezales andaluces, esos matorrales mediterráneos dominados por brezo (Calluna vulgaris) en suelos pobres en nutrientes. Gran parte de las especies de plantas de estos brezales necesitan incendios para reproducirse.

Realizado por Guillermo Ojeda, con la colaboración de Fernando Ojeda, Susana Gómez, Universidad de Cádiz, Plan INFOCA, Parque Natural de los Alcornocales, etc.

Fire in mediterranean heathlands

Prescribed burns in Valencia

May 31st, 2022 No comments

Prescribed burns has only been introduced in the Valencia region (eastern Iberia) very recently (end of 2019), and are undertaken by the Valencia government. One of the first burns was performed Castell de Castells (Alacant province) in March 2021, it was of relatively low intensity (compare with natural wildfires in the area). The area was dominated by a mediterranean shrublands with few young pines (P. halepensis). One year latter the area is a paradise of flowers; below are a few of them. Thank you to J. Fabado and X. Riera (Jardí Botànic de Valencia) for their help in the species names.

Castell de Castells burn, March 2021
Castell de Castells, May 2022
First row: Reseda (alba) valentina, Tulipa australis, Sarcocapnos enneaphylla / Second row: Linaria_depauperata, Teucrium homotrichum_ronniger, Neotinea_maculata / Third row: Argyrolobium zanonii, Phlomis lychnitis, Teucrium pseudochamaepitys / Fourth row: Anagallis arvensis, Asphodelus cerasiferous, Aphyllantes monspeliensis. Photos by JG Pausas except Linaria by B. Moreira.

Welington B.C. Delitti (1953-2022)

April 27th, 2022 1 comment

El pasado 24 de abril falleció un amigo, el Profesor Welington Delitti, después de luchar duramente, y durante más de dos años, contra un cáncer. Welington era profesor de ecología en el Instituto de Biociencias de la Universidad de Sao Paulo (Brasil), donde dirigió a numerosos estudiantes; también tuvo un papel importante en la dirección del Instituto (director 2007-2011 y subdirector 2011-2015). Su investigación se centraba principalmente en el cerrado (sabanas) de Brasil, con especial énfasis en los ciclos de materia orgánica y nutrientes y, más recientemente, en la restauración y conservación de ese maravilloso ecosistema. Durante su visita a Valencia (España) trabajó sobre el efecto de la recurrencia del fuego en matorrales de coscoja (Quercus coccifera). Hizo una aportación importante a la ecología del cerrado, y muchos de sus trabajos fueron publicados en revistas científicas brasileñas e internacionales (ver lista de publicaciones aquí). Y fue él quien me mostró ese ecosistema tan interesante por primera vez.

Personalmente era una persona entrañable, buena, y muy comprometida con la universidad y la sociedad. Era muy apreciado en su universidad por su buena gestión del Instituto de Biociencias. Su carácter afable y tranquilo le llevaba a resolver los conflictos de la forma más socialmente correcta posible. Nos enseñó una manera de funcionar, y por ello, su legado es grande.

Welington Delitti en un Cerrado de Sao Paulo, Brasil 2008 (foto: JG Pausas)
Fotos de Welington Delitti tomadas entre 2008 y 2021.
La foto de arriba-derecha, por Marcos Santos (USP Imagens, 2013); las 3 fotos de la fila de abajo y la del medio-izquierda, extraídas del Facebook de Welington (2018-2012); las otras 3 fotos son propias (2008, 2014; JG Pausas).

Orbituário:
Amoroso, ajudou os outros sem esperar nada em troca, Folha de S. Paulo, 1 mai 2022

Feedbacks in ecology and evolution

April 21st, 2022 No comments

Ecology and evolutionary biology have focused on how organisms fit the environment. Less attention has been given to the idea that organisms can also modify their environment, and that these modifications can feed back to the organism, thus, providing a key factor for their persistence and evolution [1]. We propose that there are at least three independent lines of evidence emphasising these biological feedback processes at different scales (figure below): niche construction (population scale); alternative biome states (community scale); and the Gaia hypothesis (planetary scale). Flammability is an example of niche construction [2], and the forest-savanna mosaics are an example of the alternative biome states [3] (figure below). 

The importance of feedback processes make us rethink traditional concepts like niche and adaptation. For instance, the idea of evolution as a process of adaptation to fit a pre-existing environment needs to be replaced by a ‘co-evolutionary’ species-environment approach. An implication is that the concept of species niche, and niche occupancy, is less relevant than traditionally thought. That is, organisms do not adapt to a pre-existing environment (available niche), they construct their environment and then both ‘co-evolve’. A higher level of fitness is the result of this coevolution. Feedbacks also provide an alternative framework for understanding spatial and temporal patterns of vegetation that differ from those based on gradual changes (e.g., gradient analysis and succession), and suggest that multi-stability and abrupt transitions in a given environment are common [3]; this also has implications for species’ niche modelling [4].

Earth is in transition to a new and warmer state due to anthropogenic forcing, and feedback thinking may help us understand the process. We suggest that incorporating feedback thinking and understanding how feedbacks may operate at different scales may help in opening our minds to key processes contributing to the dynamics and resilience of our biosphere.

Fig. 1. Examples of eco-evolutionary feedbacks at different organising levels: Niche construction (population; e.g. flammability), alternative biome states (community; forests and savannas) and Gaia (biosphere). The signs of the feedbacks indicate the most common type of feedback for each example. Evolutionary feedbacks represent the evolutionary processes at the different scales (from selection at the micro-evolutionary scale to the acquisition of key macro-evolutionary innovations). From [1].

References

[1] Pausas J.G. & Bond W.J. 2022. Feedbacks in ecology and evolution. Trends Ecol. Evol. [doi | pdf]

[2] Pausas J.G., Keeley J.E., Schwilk D.W. 2017. Flammability as an ecological and evolutionary driver. J. Ecol. 105: 289-297. [doi | wiley | pdf]

[3] Pausas J.G. & Bond W.J. 2020. Alternative biome states in terrestrial ecosystems. Trends Plant Sci. 25: 250-263. [doi | sciencedirect | cell | pdf]

[4] Pausas J.G. & Bond W.J. 2021. Alternative biome states challenge the modelling of species’ niche shifts under climate change. J. Ecol. 109: 3962-3971. [doi | wiley | pdf]

Fire-released seed dormancy

April 8th, 2022 No comments

Many plants concentrate their seedling recruitment after the passage of a fire. This is because postfire conditions are especially optimal for germination and establishment of many species as fires create extensive vegetation gaps that have high resource availability, minimal competition, and low pathogen load. Thus we propose that fireprone ecosystems create ideal conditions for the selection of seed dormancy as fire provides a mechanism for dormancy release and optimal conditions for germination [1]. We compiled data from a wide range of fire-related germination experiments for species in different ecosystems across the globe and identified four dormancy syndromes: heat-released (physical) dormancy, smoke-released (physiological) dormancy, non-fire-released dormancy, and non-dormancy. In fireprone ecosystems, fire, in the form of heat and/or chemical by-products (collectively termed ‘smoke’), are the predominant stimuli for dormancy release and subsequent germination, with climate (cold or warm stratification) and light sometimes playing important secondary roles. Fire (heat or smoke)-released dormancy is best expressed where woody vegetation is dense and fires are intense, i.e. in crown-fire ecosystems (e.g., mediterranean-type ecosystems). In grassy fireprone ecosystems (e.g. savannas), where fires are less intense but more frequent, seed dormancy is less common and dormancy release is often not directly related to fire (non-fire-released dormancy). Fire-released dormancy is rare to absent in arid ecosystems and rainforests. Heat-released dormancy can be traced back to fireprone floras in the ‘fiery’ mid-Cretaceous, followed by smoke-released dormancy, with loss of fire-related dormancy among recent events associated with the advent of open savannas and non-fireprone habitats. Anthropogenic influences are now modifying dormancy-release mechanisms, usually decreasing the role of fire. We conclude that contrasting fire regimes are a key driver of the evolution and maintenance of diverse seed dormancy types in many of the world’s natural ecosystems.

Fig. 1. Percentage germination of 68 populations or species subjected to simulated fire- (y axis) and summer-type (warm stratification) temperature (x-axis) (C., Cistus; F., Fumana; U., Ulex; A., Acacia; M., Mimosa). Points above the dotted line (1:1) have higher germination levels after fire heat than after summer heat. Note that all points at or below the line are for species in savannas [S], while the others are from mediterranean shrublands and other crown-fire ecosystems. That is, in crown-fire ecosystems, fire is the most likely selective agent for dormancy. From [1].
Fig. 2. Dated phylogeny for major clades in the New and Old World Cistaceae together with closely related ancestral clades. Pie charts at the tips show the fraction of species that occur in crown-fire ecosystems (red), surface-fire ecosystems (orange), those with physical dormancy – hard seeds (green), and those with heat-released dormancy (blue). Blank sectors mean that the trait is absent. Letters at the tips refer to growth forms in the clade (T, tree; S, shrub or subshrub; H, herb/annual). Black dots indicate the crown age of diversification of the corresponding clade. From [1].

References

[1] Pausas J.G. & Lamont B.B. 2022. Fire-released seed dormancy – a global synthesis. Biological Reviews  [doi | pdf | supp. mat. | data (figshare)]

Antoni Escarré (1941-2022)

March 9th, 2022 1 comment

El pasado sábado 5 de marzo falleció Antoni Escarré Esteve a los 80 años y en su tierra natal, Alacant. Era Doctor en Biología por la Universitat de Barcelona, catedrático de ecología en la Universitat d’Alacant, y fundador del departamento de ecología de esa universidad. Escarré fue uno de los pioneros de la ecología terrestre en nuestro país, amigo muy cercano a los ecólogos catalanes más eminentes (Ramón Margalef, Jaume Terradas). Su pasión naturalista le llevó a trabajar con una gran diversidad de organismos tanto animales como plantas. Realizó trabajos clave para entender el ciclo de la materia y nutrientes, la ecofisiología de plantas, y la fauna en ecosistemas mediterráneos; posteriormente se enfocó en ecosistemas tropicales. Nunca dejó de mostrar curiosidad por la naturaleza, incluso en su jubilación, ya alejado de obligaciones docentes o investigadoras. Su última tesis doctoral se leyó en 2019.

Una de sus actividades destacadas fue la de dirigir un doctorado sobre desarrollo sostenible del bosque tropical en Cuba, en el cual se han realizado un centenar de tesis doctorales. Este programa ha sido fundamental para el desarrollo de la ecología en Cuba. Por ello Escarré es muy conocido y apreciado por todo naturalista cubano, y fue investido Doctor Honoris Causa por la Universidad de Pinar del Río en Cuba en 2007.

Antoni Escarré también participó en la vida política de la Comunidad Valenciana y ostentó diversos cargos políticos durante los periodos socialistas, tales como Conseller d’Educació, Cultura i Ciència (1989-1991) y posteriormente, Conseller de Medi Ambient (1991-1993). Se dice que era una persona demasiado sincera y normal (es decir, informal para los políticos) para la política, y pronto volvió a la docencia en la UA. Entre sus aficiones destacaba el hockey, fue jugador y entrenador, y llegó a ser Presidente de la Federación de Hockey de la Comunidad Valenciana (1986).

A nivel personal era encantador, culto, bueno, sincero, alegre, comprometido, generoso e inteligente; Terradas, con quien compartió numerosas vivencias, decía que era imposible aburrirse con él. En los últimos años lo hemos visitamos varias veces en su casa, y siempre estaba jovial, buscando cualquier excusa para celebrar algo e invitarnos a una copa de cava. Las veladas en su casa, donde discutíamos de ciencia y política, a menudo en compañía de alguien de Cuba, eran entrañables.

Le echaremos de menos

La primera fotografía (en blanco y negro): A. Escarré cuando era conseller de cultura (1990), en compañía de Enric Valor. El resto de fotografías: Antoni Escarré con algunos de sus colaboradores del doctorado cubano: Vicente Berovides, Rubén Chamizo y Josabel Belliure

Ucrania – decálogo personal

March 6th, 2022 No comments

No soy experto en conflictos, ni en Rusia, ni en Ucrania, pero no puedo evitar expresar mi opinión. Las reacciones y razonamientos que se dan por muchos políticos y medios de comunicación me parecen extremadamente pobres.

1) Condeno rotundamente la invasión de Ucrania por parte de Rusia. El gobierno ruso se comporta de manera extremadamente imperialista, autócrata, e inhumana (igual que lo hizo en Siria, e igual que EEUU en Irak, y en tantos otros sitios).

2) Estoy en contra de que se solucionen conflictos y desacuerdos mediante violencia, y especialmente mediante guerras. Los líderes que proponen guerras son los menos perjudicados, los ciudadanos de a pie, los más perjudicados. No es cuestión de pacifismo, es cuestión de que las guerras enquistan los conflictos, no los solucionan.

3) Ante una acción violenta, hay que apoyar a los oprimidos, independientemente de quien tenga más razón en el conflicto. El desequilibrio de fuerzas es desproporcionado, es un abuso de superioridad.

4) Solidaridad con los ciudadanos en Rusia que están manifestandose en contra de esta guerra; arriesgan mucho. Y solidaridad con los desertores del ejercito ruso; arriesgan muchísimo. Hay que evitar que aparezca una rusofobia; estamos en contra de las decisiones del gobierno ruso, no de los ciudadanos. Tanto en Rusia como en Ucrania (y España) hay fascistas, comunistas, demócratas, neoliberales, anarquistas, ecologistas, apolíticos, y un largo etc.

5) Esta guerra es un fracaso de la humanidad, y en especial de Europa y EEUU, ya que no se ha conseguido (¿o querido?) evitar, y hasta el momento no se ha sabido detener. Había margen de maniobra antes de que empezara. Los tímidos intentos por algunos políticos (p.e., Macron, etc.) no fueron suficientes, y dadas las posibles consecuencias, se debería haber hecho mucho mucho más esfuerzo en negociar una solución. Quizá podría haber ayudado contar con  un panel de expertos en conflictos, con premios Nobel de la Paz, con la ONU, o con reconocidos líderes mundiales (Papa, Dalai Lama), etc. Justificar la guerra diciendo que con Putin no se puede negociar es de una pésima calidad democrática. Es conocido desde hace mucho tiempo que Rusia no quiere bases de la OTAN en su frontera, igual que EEUU no quieres pro-rusos en la suya (Cuba). ¿Qué haría EEUU si México quisiera instalar una base militar rusa? ¿Es necesaria la OTAN? Es difícil imaginar que haya valido la pena empeñarse en que la OTAN tenga bases militares en Ucrania. ¿Dónde está la ONU?

6) Estoy en contra de enviar armamento a Ucrania, que sólo alimenta la guerra y no soluciona el conflicto. La cantidad de armamento que requeriría Ucrania para “ganar” a Rusia es ingente. Además, enviando armas hay peligro de que la guerra se “mundialice” e incluso de que se use armamento nuclear. Todos los esfuerzos se deben centrar en parar la guerra, no en alimentarla. Enviar armas es una acción fácil y una manera de lavarse las manos; pensar que con eso se está ayudando al pueblo Ucraniano es engañoso y peligroso. La guerra no la ganará ni Putin ni Ucrania, la perderemos todos. Además, se alimenta el comercio y la corrupción que hay en torno al negocio del armamento y las guerras. ¿Enviamos armas a Palestina?

7) Los que dicen que la izquierda apoya a Rusia desconocen lo que significa ser de izquierdas en el siglo XXI.

8) Celebro que Europa facilite la acogida de refugiados (pero demuestra que si no se realizó lo mismo en otros conflictos previos fue por falta de ética o directamente por racismo).

9) Tengo mis dudas de que las sanciones impuestas por la Unión Europea a Rusia sean realmente eficaces porque: (1) afectarán a la población rusa (no sólo a los responsables de la guerra); (2) la Unión Europea tiene una gran dependencia comercial de Rusia (gas, cereales, minería, etc.), y esta podría tomar represalias contra Europa (guerra económica); y (3) Rusia es una gran potencia militar y está geográficamente muy cerca (en la misma Europa), por lo que no parece muy inteligente enfrentarse a ella. 

10) A menudo los medios de comunicación cuentan la guerra como si fuera una película, presentando a los ucranianos casi como héroes que están defendiendo valientemente sus causas y resistiendo los ataques. La verdad es que cada día hay más destrucción y muertos en Ucrania, y más desplazados, mientras el ejército ruso sigue avanzando inexorablemente.

Lecturas sugeridas

Geografía de Ucrania

Gestión posincendio y fajinas

February 1st, 2022 No comments

La pérdida de suelo es de las peores cosas que le puede suceder a un ecosistema, ya que tarda muchísimo en recuperarse. Por ello, después de un incendio, en los sitios donde hay posibilidad de pérdida de suelo, se aconseja realizar medidas rápidas de protección del suelo, tales como poner paja, ramas, haces de ramas, ramas trituradas, troncos en fajinas, o cordones de restos de cortas. Estas acciones reducen el impacto de las gotas de agua de la lluvia, generan condiciones de humedad para la regeneración de la vegetación, y reduce el movimiento del suelo. En una zona incendiada, la extensión de zonas con potencial de erosión depende, especialmente, del tipo suelo, la pendiente, y el uso previo de la zona. En las zonas sobre calizas duras de la costa mediterránea, las extensiones con potencial de erosión posincendio suelen ser reducidas, a veces puntuales; nunca en todo un incendio.

Actualmente estamos viendo que después de incendios, se están realizando fajinas con troncos y ramas en zonas donde no se espera pérdida de suelo, tales como zonas planas, pedregosas, incluso en bancales con muros bien conservados (ver fotos abajo). Para ello se cortan los pinos y algunos arbustos (a veces incluso especies rebrotadora) y se amontonan a modo de fajinas. Estas acciones parecen un gasto económico poco justificable, además de perder los beneficios de los árboles quemados en pie.

Cabe recordar que los árboles muertos en pie benefician a la regeneración porque también disminuyen el impacto de las gotas de lluvia en el suelo, mantienen cierta humedad, captan agua de la niebla, y sirven de posadero para aves que traen semillas y que contribuyen a la regeneración. Además de ser hábitat para mucha fauna (principalmente invertebrados y algunas aves). Cuando los árboles muertos caen, proporcionan materia orgánica y nutrientes al suelo. Sería necesaria una justificación para cortarlos, y para concentrar la biomasa en pocos puntos (ver fotos).

Las siguientes fotos corresponden a ejemplos de fajinas de troncos y ramas realizadas después de incendio, en zonas que no se espera erosión por estar en bancales, en zonas pedregosas, o en zonas con poco pendientes. Fotos tomadas en dos incendios de la Comunidad Valenciana: Llutxent (noviembre de 2018) y Azuébar (diciembre de 2021).

Fajinas en bancales, Azuébar

Image 1 of 9

Más información:

Llutxent y la perdida de suelo, jgpausas.blogs.uv.es/2018/10/30

Lo que no se debe hacer después de un incendio, jgpausas.blogs.uv.es/2015/08/1

Postfire management in Turkey

January 27th, 2022 1 comment

This post complements the letter published today in the Science [doi] – A version of that letter is also available in Turkish here.

Turkey was hit hard by wildfires in 2021, with a record of about 203,000 ha burnt. Most of the area burnt was covered by Mediterranean Pinus brutia forests. Pinus brutia is not a fire-resistant trees, it dies after a fire; however, they have serotinous cones thus after fire the seeds are dispersed and new individuals recruit few months later. This forest also includes many shrubs able to resprout or germinate after fire. Thus natural regeneration was expected in most of the affected area. In fact, 4 months after fire, we already observed pine seedlings and many species resprouting [link]. To preserve this ecosystems, it is important to preserve their regeneration potential. Usually, quick postfire management is only needed if soil losses are likely; in those environments, soil losses typically occurs in only a small proportion of the landscape.

However, the Turkish government is cutting all dead trees (salvage logging). In many places, heavy machinery is being used and forest roads are being opened. In some cases, logging is followed by seeding or by terracing and new tree planting. That is, in some places they are transforming an ecosystem to an artificial afforestation. Thus the postfire management actions are more disturbing than the fire. And these postfire actions are taking place in both unprotected public forests and in conservation areas (e.g. Marmaris National Park).

It is worth remembering that standing dead trees have many ecological functions such as to reduce the impact of raindrops on the ground (i.e., reducing erosion), maintain some humidity, capture water from fogs, serve as perches for birds that bring seeds and contribute to the regeneration, and are habitat for many fauna (mainly invertebrates and some birds). And when dead trees fall down, they provide organic matter and nutrients to the soil. 

We urge the Turkish General Directorate of Forestry to stop degrading ecosystems and move toward more ecologically sustainable forest management.

All photos below were Pinus brutia forests.

Postfire salvage logging + terracing + plantation in Marmaris National Park (see also this video)

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Postfire salvage logging of burned trees in the Marmaris area

 

Examples of destroying potential natural postfire regeneration in Antayla, Turkey. Click the image to enlarge. Photos: link

References

[1] Tavsanoglu, Ç. & Pausas J.G: 2022. Turkish postfire action overlooks biodiversity. Science [doi | pdf | Turkish version]

[2] Marmaris postfire regeneration, jgpausas.blogs.uv.es/2021/12/05/

Megafauna history and plant defense traits

January 10th, 2022 No comments

The role of large herbivores in explaining broad-scale ecological pattern has often been underestimated [1]. Plants have defenses against large herbivores (e.g., spines, high wood density [2]). And many continents had abundant large herbivores (megafauna) that were extinguished in Pleistocene (except in Africa). In a recent paper [3] we asked, to what extent the past distribution of extinct magafauna explains current geographical distribution of plant defense traits in the Neotropics (South & Central America). We fond that a significant proportion of the variance in the distribution of wood density, leaf size, stem spines, and leaf spines are explained by variable related to past megafauna (richness and body mass).

We defined 3 antiherbiomes in South America, that is, regions with characteristic plant defenses, environmental conditions, and Pleistocene megafauna, as follows: Small-Leaves-Thorny (SLT): thorny and small-leaved plants, in arid, cold and nutrient-rich ecosystems, containing numerous extinct and extant large grazers. Intermediate-Leaves-Woody (ILW): intermediate leaf sizes and levels of chemical defenses, and very high wood density, in moist and hot climates, and extremely nutrient-poor soils; and a high extinct megafauna richness, especially in relation to small browsers and mixed-feeders. Broad-Chemically-defended-Leaves (BCL): very large leaves with chemical defenses, mostly associated with moist climates and intermediate fertility soils, with few but large extinct megafauna species, especially browsers. Similar antiherbiomes can be observed in current Africa. These antiherbiomes represent one of the most striking broad-scale anachronisms in ecology.

We estimated that in South America, savannas occupied about 10 millions of Km2 during the Pleistocene, ca. 63% of them were converted to forests (44% to moist forests, 19% to dry forests) after the megafauna extinction (biome shifts [4]), and ca. 37% remains as savanna (stable). This suggests that South America was a savanna-dominated continent, much more similar to Africa than today, and that a large proportion of South American forests are the result of megafauna extinctions.

Overall our results suggest that past (extinct) large herbivores explain an important proportion of the variability of current plant traits and community assemblies.

 

Fig. 1. Left: Distribution of the 3 anti-herbiomes. Right: Hypothesized distribution of savanna during the Pleistocene (coloured areas; based on the distribution of extinct megafauna), that currently are savanna (in yellow), moist forests (dark green) and dry forests (light green). From [3]
Fig. 2. Reconstruction of Pleistocene savanna (ILW antiherbiome) with Taxodon platensis (a mixed feeder) next to the tree Bowdichia virgilioides (sucupira-preto; Fabaceae), and a Notiomastodon in the background. Artist: Júlia d’Oliveira

Fig. 3. Additional reconstructions of the Pleistocene Brazilian savannas from [5]. Artist: Júlia d’Oliveira

 

References

[1] Pausas JG & Bond WJ. 2019. Humboldt and the reinvention of nature. J. Ecol. 107: 1031-1037. [doi | jecol blog | jgp blog | pdf]

[2] Dantas V & Pausas JG. 2020. Megafauna biogeography explains plant functional trait variability in the tropics. Glob. Ecol. & Biogeogr. [doi | pdf | data:dryad | blog ]

[3] Dantas V., Pausas J.G. 2022. The legacy of Southern American extinct megafauna on plants and biomes. Nature Comm. 13: 129 [doi | pdf | data & codes] – New!

[4] [2] Pausas JG & Bond WJ. 2020. Alternative biome states in terrestrial ecosystems. Trends Plant Sci. 25: 250-263. [doi | sciencedirect | cell | pdf]

[5] Pansani et al. 2019. Isotopic paleoecology (δ13C, δ18O) of Late Quaternary megafauna from Mato Grosso do Sul and Bahia States, Brazil. Quat Sci Rev, 221, 105864. 

Marmaris postfire regeneration

December 5th, 2021 No comments

During last summer, over 170,000 ha burnt in Turkey. One of these fires was the Marmaris fire, a fire of about 12,500 ha in SW of the country. The area includes part of the Marmaris National Park and an Special Environmental Protection Area. Most of the area were covered by Pinus brutia forests, a Mediterranean pine that has some serotinous cones.

Four months after the Marmaris fire, I visited the area together with Çagatay Tavsanoglu. Some plants were resprouting and some geophytes flowering (Cyclamen, Arisarum). Pine seedlings had started to germinate; there were also many other seedlings but still too small to identify them (e.g., Cistus species). Below are a few examples of plants that were regenerating after the fire (click on the photos to enlarge them).

 

Conferencia

November 13th, 2021 No comments

El pasado día 10 de noviembre impartí una conferencia titulada ‘Fuego: Incendios y biodiversidad’ en la delegación del CSIC de Valencia, con motivo de la celebración de los 25 años del CIDE (Centro de Investigaciones sobre Desertificación). Aquí la tenéis disponible.

hora:minuto

0:00 a 0:04 – Presentación por el director del CIDE
0:04 a 0:47 – Conferencia propiamente dicha
0:47 a 1:24 – Preguntas del público

Podéis ver otros vídeos con charlas y entrevistas en mi web y en otras entradas de este blog: entrevistas (2021), charla IVIA (2017,) fragmentos de documentales, documental ‘La huella del fuego’ (TVE 2016), documental en ‘el cazador de cerebros’ (La2 TVE 2020).

Deforestation and COP26

November 5th, 2021 No comments

It is very nice to see that COP26 have decided to halt deforestation and accelerate the restoration of natural ecosystems (link). We hope this time it will be effective and quick. Past attempts such as REDD+ or the 2014 New York Declaration on Forest (PDF) had limited success; deforestation (logging and clearing for farming or mining) continued even in regions with high biodiversity value (e.g., the Amazon rainforests, the savannas of Cerrado, the dry forest of the Chaco, and Indonesian closed-canopy tropical forests; Figs. 1,2,3,4 below). Deforestation and forest fragmentation are also the main reasons behind the large number of fires occurring in rainforests (native rainforests are non-flammable).

We also hope the COP26 decision will stimulate the conservation not only of forests but also other ecosystems with high biodiversity values, including wetlands, savannas, grasslands, and shrublands. For instance, Brazilian savannas are well recognized as a biodiversity hotspots (Cerrado region) and it is the area that have lost most of their natural habitat in Brazil (Fig. 2), followed by the Pantanal (world’s largest tropical wetland). Note that wetlands provide multiple benefits, including biodiversity, carbon sequestration, and the conservation of the water cycle (and of the climate). Similarly, the Paraguayan Dry Chaco is quickly losing the native vegetation (Fig. 3).

Fig. 1. Examples of fast deforestation in two areas with high biodiversity value (in the Brazilian Amazon): Fishbone type deforestation pattern between 2000 and 2019 (top), and rectangular type deforestation pattern between 2013 and 2017 (bottom). The most deforested images (right) also show the smoke from fires associated with deforestation. Source: NASA Earth Observatory
Fig. 2. Native habitat lost in Brazil (as proportion of the area, between 1985 and 2020) by states (left) and by biogeographic regions (right). Source: elaborated from data in MapBiomas.org
Fig. 3. Deforestation in different South American ecosystems, from https://insights.trase.earth/insights/cop26-must-commit-to-zero-deforestation/
Fig. 4. Degradation of Indonesian ecosystems: Annual primary forest cover loss (in Mha) in Sumatra and Kalimantan (a), and remaining forest cover in 2001 and 2019 in peatland (b) and non-peatland (c) ecosystems. Deforestation of peatlands and artificial drainage are major cause of peatland fires in the area, and those fire are a major sources of CO2 emissions. From Nikonovas et al. (2020).