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 of 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 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).

Carob tree postfire: fire severity

October 19th, 2021 No comments

One of the major factors generating dynamic in Euro-Mediterranean landscapes is rural abandonment and the consequent expansion of oldfields [1]. This oldfields are been colonized by fast-growing flammable plants, and this has occurred now for few decades [2]. Thus wildfires often spread through oldfields [2], and in fact the increasing of oldfields is the main driver of the increased fire activity in Spain since the 70’s [2]. One example of Mediterranean crop is the Carob tree [1]. Carob trees (Ceratonia siliqua; Fabaceae) are evergreen tree that produce edible pods, used in the past mainly as animal fodder; currently it is also used as substitute for chocolate (pods are sweet; in fact they can be eaten raw from the tree).

A recent wildfire in Azuébar (August 2021, eastern Spain) burned a landscape that had many abandoned Carob tree groves. These trees burned at a range of seventies (degree of consumption). So perhaps, by looking at the carob trees across the burned landscape we could map the severity of a wildfire! In the past we estimated fire severity using the degree of consumption of the pine canopy (Pinus halepensis) [3].

Pictures taken in September 2021, one month after the Azuébar fire.

Figure 1. Carob tree unburned (top left) and burned with different severity: with leaves unconsumed (top right), with leaves consumed (mid left), with main trunk consumed (mid right), with most wood consumed (bottom, left), with everything consumed (bottom right). All pictures taken 1 month after a fire in Azuébar, eastern Spain. Photos: JG Pausas.

References

[1] Pausas JG, Bonet A, Maestre FT, Climent A. 2006. The role of the perch effect on the nucleation process in Mediterranean semi-arid oldfields. Acta Oecol. 29: 346-352. [pdf] [doi] [ScienceDirect]  

[2] Pausas JG & 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]

[3] Pausas, J.G., Ouadah, N., Ferran, A., Gimeno, T. & Vallejo, R. 2003. Fire severity and seedling establishment in Pinus halepensis woodlands, eastern Iberian Peninsula. Plant Ecol. 169: 205-213 . [doi | pdf]

Reconciling Gleason’s and Clements’ views

September 30th, 2021 No comments

The question of whether species are organised as collectives of integrated interacting assemblages (Clements’ community concept) or behave individualistically (Gleason’s community concept) is a century-old debate in ecology that is still unresolved. In a recent article, we are reconciling the two approaches [1].

The Gleasonian view suggests that communities are assembled by species that respond individualistically along environmental gradients and thus cannot form bounded units (Fig. 1A). However, in many world landscapes, for a given climate, strikingly different biomes with sharp boundaries co-occur forming landscape mosaics. These mosaics are typically formed by a closed biome (forests) and open (non-forest) biome (e.g., grassland, savanna, shrublands). These two alternative biome states (ABSs [2]) are maintained by different feedback processes and have radically different species with contrasting shade and disturbance tolerance traits [2].

Under the individualistic view of species along climatic gradients, the overlapping response curve along a climate gradient (Fig. 1A) may indicate plant coexistence (and potentially competitive interactions); however this is true only if they occur in the same biome (Fig. 1B). That is both Gleason’s individualistic view (within biome) and Clements’s organismic view (across biomes) are complementary; both perspective of community remain useful in ecology.

The consequence is that fitting species distribution models or using climate limits in modelling for projecting future species distributions are inappropriate for extensive regions with alternative biome states. One way to improve these predictions would be to consider the presence or absence of forest shade in the modelling [1].

Figure 1. Classical (Gleasonian) pattern of species response curves along a climate gradient (A), and the alternative pattern along the same climatic gradient when there are ABSs (B). Note that in the driest and the wettest section of the gradient, we find open (e.g., grassland) and closed (forest) biomes, respectively; but at intermediate levels of the gradient, both are possible depending mainly on the disturbance regimes and feedback processes [2). Thus, under the intermediate levels of the gradient, species that may seem to coexist when considering climate only (A) are not really coexisting but occurring in drastically different biomes (B). From [1].

References

[1] Pausas J.G. & Bond W.J. (in press). Alternative biome states challenge the modelling of species’ niche shifts under climate change. J. Ecol. [doi | pdf]

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

Incendios forestales: no todo es cambio climático

August 18th, 2021 No comments

Este artículo apareció en TheConversation, ElDiario.es, LaMarea, y aquí, entre el 18 y 19 de agosto de 2021. Aquí incluyo una versión previa, ligeramente más larga que la publicada en el resto de medios.

En estos días de olas de calor se están produciendo grandes incendios en el Mediterráneo, especialmente en Turquía, Grecia, Italia, Argelia. Situaciones parecidas se están dando en otras partes mundo (California, Canada, Siberia, etc.). Y algo similar vivimos el verano pasado. Por ello se entiende que, repetidamente, me pregunten si todos estos incendios son consecuencia del cambio climático. La respuesta corta es que el cambio climático facilita los incendios (facilita la propagación del fuego y extiende la temporada de incendios), pero no determina que haya incendios. A continuación intento responder de manera más detallada.

Los ingredientes

Para que se den incendios se necesitan al menos tres ingredientes, que además deben darse de forma simultánea [1]. Estos ingredientes son: igniciones (naturales o humanas), vegetación densa y continua (combustible), y sequía. La relación de estos factores con los incendios no es lineal, sino de tipo umbral. Es decir, hay un nivel de igniciones, de continuidad de vegetación, y de sequía, a partir de los cuales la probabilidad de incendio aumenta de manera exponencial (se dispara).

Cuando se superan los tres umbrales se generan megaincendios de difícil control. Y estos umbrales varían con las condiciones meteorológicas. Concretamente, son muy bajos cuando las temperaturas son especialmente elevadas (olas de calor), la humedad baja, o los vientos son fuertes. Es decir, en estas condiciones, se necesita menos igniciones, menos combustible, y menos sequía para que se generen incendios. Por lo tanto, en esas condiciones particulares los incendios son mucho más probables, siempre y cuando haya igniciones y continuidad del combustible.

Efecto de las olas de calor y vientos fuertes (flecha roja) en modificar los umbrales que generan incendios. Fuente: [1]

El reciente incremento en sequías y olas de calor está asociado al cambio climático (ver informe IPCC 2021). Sin embargo, los incrementos en igniciones y en continuidad de la vegetación son bastante independiente del clima. El número de igniciones (tanto accidentales como provocadas) está muy relacionado con la actividad humana, y especialmente con actividades urbanas en zonas forestales o semiforestales. La continuidad de la vegetación está relacionada principalmente con el abandono rural y con plantaciones forestales densas sin una gestión apropiada.

El incremento de incendios en España en los años 70 y 80 se explica especialmente por el aumento en continuidad de la vegetación debido al abandono rural [2]. El cambio climático tuvo un papel poco relevante. A medida que dejamos que avance el cambio climático, el papel relativo del clima en los incendios aumenta. Hay que recordar que en España, y en muchos países europeos, la masa forestal está en aumento, a pesar de los incendios [3].

Por lo tanto, el incremento de las temperaturas, olas de calor y sequías facilita en gran manera los incendios, pero se requieren también igniciones y vegetación continua. Y eso es una buena noticia. Reducir las igniciones y generar discontinuidades en la vegetación es más sencillo que reducir el cambio climático (que también es necesario).

¿Qué podemos hacer?

La política de tolerancia cero a los incendios no ha funcionado en ningún país del mundo. Ni en países con presupuestos en extinción muy elevados. Eliminar los incendios de nuestros paisajes es imposible y contraproducente [4], especialmente en el marco del cambio climático. Debemos aceptar un cierto régimen de incendios y aprender a convivir con ellos.

El reto de la gestión es crear condiciones que generen regímenes de incendios sostenibles tanto ecológica como socialmente. Para conseguir esto no hay una receta sencilla ni única. Por ejemplo, no es lo mismo gestionar una zona donde los incendios se propagan por el paisaje principalmente gracias a vientos fuertes, que si lo hacen debido a la existencia de grandes extensiones forestales homogéneas [5]. En el primer caso, gestionar las igniciones puede ser lo más importante. En el segundo, la clave puede estar en gestionar el combustible.

Los incendios son especialmente peligrosos cuando se acercan a zonas semiurbanas (en la interfaz urbano-forestal) y es donde la gestión es más importante. Una manera de reducir los incendios es generar discontinuidades (horizontales y verticales) en la vegetación. Existen diversas herramientas para ello, tales como: realizar cortas y quemas prescritas, introducir herbívoros (salvajes o ganado), alternar sistemas forestales con cultivos y permitir que ardan los incendios que sean poco agresivos. Iniciativas como incentivar la actividad rural local (agricultura y ganadería extensiva) o la resilvestración (rewilding) pueden actuar en la buena dirección. Cada una de estas herramientas puede ser válida dependiendo del sitio y las condiciones, y dada la complejidad del sistema, puede ser importante utilizar una diversidad de herramientas. Ninguna de ellas elimina los incendios, pero reducen su probabilidad, su tamaño, y su intensidad.

En momentos de olas de calor o de vientos estivales fuertes (por ejemplo, durante los ponientes en Valencia) sería importante limitar las actividades humanas en el monte. Es decir, limitar el paso de vehículos y personas, incluyendo el acceso a segundas residencias situadas en entornos forestales. Si durante épocas de riesgo por pandemia se ha limitado la movilidad, quizá en momentos de máximo riesgo de incendios también se podría limitar la movilidad en zonas forestales y semiforestales. Esto es importante porque los incendios se producen cuando las igniciones coinciden con condiciones meteorológicas adversas en paisajes con suficiente vegetación. En esos escenarios, reducir las igniciones es clave.

También se podría limitar la interfaz urbano-forestal. Es decir, reducir la expansión de urbanizaciones y polígonos industriales en zonas rurales y naturales. Esta expansión, además de los efectos ambientales bien conocidos (en biodiversidad, especies invasoras, contaminación lumínica y visual, etc.), también constituyen una fuente de igniciones y hacen la vegetación más inflamable. Además, ponen en riesgo a personas e infraestructuras, y por lo tanto, convierten en catastróficos (socialmente) incluso a regímenes de incendios ecológicamente sostenibles. Los mecanismos para limitar estas zonas pueden ser diversos, incluyendo la recalificación de terrenos (a no urbanizables), o la  implementación de tasas por construir en áreas con alto riesgo de incendios (pirotasas), entre otros. Y la planificación urbanística requiere considerar a los incendios, así como exigir estrategias de autoprotección alrededor de viviendas y la realización de planes de evacuación. 

Otra medida importante es restaurar los humedales y otros ecosistemas litorales, ya que, a parte de los beneficios para la biodiversidad, mantienen el ciclo del agua y contribuyen a la conservación del clima [3]. La degradación de la costa (desecación de los humedales y la sobre-urbanización) contribuye a la reducción de la precipitación [3].

Y en cualquier caso, hay que reducir el consumo de combustibles fósiles. Esto ayudaría a frenar el aumento de CO₂ atmosférico, y así reducir la velocidad del cambio climático y la frecuencia de olas de calor. Y no solo por los incendios.

Referencias

[1] Pausas J.G. & Keeley J.E. 2021. Wildfires and global change. Frontiers in Ecology and Environment 19(7) [doi | wiley | pdf | brief for managers]

[2] 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]

[3] 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]

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

[5] Keeley, J.E. & Syphard, A.D. 2019. Twenty-first century California, USA, wildfires: Fuel-dominated vs. wind dominated fires. Fire Ecology, 15, 24.

The cleaning effect of fire: Lizards & parasites

July 14th, 2021 No comments

Early humans and native cultures have used fire for clearing the ground from parasites and diseases, and some agricultural societies use fire to reduce livestock diseases [1,2]. In such cases, fire provide an ecosystem service to humans [2]. We recently asked to what extent this ‘cleaning effect‘ of fire is also observed in the wild, that is, whether wildfires may remove parasites and thus provide some benefits to wildlife [3]. To answer this question, we compared the presence of ecotoparasites (mites,Ophionyssus) in lizard populations of Psammodromus algirus living in recently burned areas with those in adjacent unburned areas, in eastern Spain. Our results suggest that many individuals of P. algirus survive fire (the smoke of the fire acts as a cue for quickly moving to safe microsites [4], e.g., crevices, under rocks, among roots; refugia [5]); and those that survived (and live in the postfire environment) have less ecotparasites (mites) than those living in unburned conditions. That is wildfires produce a ‘cleaning effect’ by reducing lizard ectoparasites in the postfire conditions. Fire, by disrupting the host-parasite interaction, provides a window of opportunity for lizards to avoid the negative effects of ectoparasites. We propose that wildfires likely fulfill a role in controlling vector-borne diseases and pathogens for other species, but this ecological effects have been largely overlooked.

Fig. 1. Probability of lizards infection by mites in relation to lizards’ size (snout-vent length) for recently burned areas (red) and for the corresponding paired unburned (blue). Lines are predicted values (and confidence intervals) from [3].
Fig. 2. Psammodromus algirus enjoying a clean (parasite-free) environment after a fire. Photo: Lola Álvarez-Ruiz
Fig. 3. Pictures of mites (genus Ophionyssus; in different stages) found under the scales of P. algirus, from [3]
Fig. 4. Art work on the paper by Josep Serra, 6/2021

References

[1] 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]

[2] Pausas J.G. & Keeley J.E. 2019. Wildfires as an ecosystem service. Front. Ecol. Environ. 17: 289-295. [doi | pdf]

[3] Álvarez-Ruiz L, Belliure J, Santos X., Pausas JG. 2021. Fire reduces parasite load in a Mediterranean lizard. Proceed. Royal Soc. B. [doi | pdfNew!

[4] Álvarez-Ruiz L, Belliure J, Pausas JG. 2021. Fire-driven behavioral response to smoke in a Mediterranean lizard. Behav. Ecol. [doi | oup | PDF]

[5] Pausas J.G. 2019. Generalized fire response strategies in plants and animals. Oikos 128: 147-153 [doi | pdf]

Wildfires and global change: the threshold approach

June 3rd, 2021 No comments

To generate wildfires we need some specific components (ignitions, fuel, and right conditions). Traditionally, this has been explained using the triangle approach [1] or the 4-switches approach [2]. We propose a more mechanistic model to explain wildfires, the threshold approach [3]. Under this view, wildfires occur when three thresholds are crossed (ignition, continuous fuel, and drought); and fire weather moves these thresholds to lower values and so it triggers the occurrence and spread of wildfires (Fig. 1). The size and duration of the fire largely depend on how long the fire weather lasts and the extent of the area containing suitable fuel.

Climate change increases the conditions conductive to fire, and thus it also increases the frequency in which some of these thresholds are crossed, extending the fire season and increasing the frequency of dry years. However, climate-related factors do not explain all the complexity of global fire regime changes as human factors are extremely important: humans shifts ignition patterns and modify fuel structure. Humans cause ignitions directly by accident or arson, but also indirectly by altering fuels that can make them more susceptible to ignitions (vegetation openings). Humans also modify fuel continuity, either reducing it (eg fragmentation) or increasing it (eg fire suppression). For instance, in many Mediterranean ecosystems, the drought threshold is crossed annually, and vegetation cover (fuel) is usually high enough for fire spread; thus, ignitions are a key factor. Larger populations of humans in the wildland-urban-interface will likely lead to increased ignition rates, and consequently higher probability of ignitions coinciding with extreme weather events to generate wildfires.

Fig. 1. Probability of fire occurrence vs ignitions; fire spread vs landscape fuel continuity; and, fuel flammability vs drought. In each of the three graphs, vertical lines indicate the thresholds. In all cases, fire weather (strong wind, high temperature, or low humidity) moves the curve (and the threshold) towards lower values (thick red arrow; i.e. , saturation is reached at lower values of the x axis), with the consequence of increasing the probability of an ignition resulting in a fire, the fire spread (for a given landscape configuration), and the flammability of the vegetation (fuel dries out quicker). The flow chart indicates the main factors affecting the fire drivers: growing population (in or near wildlands); fuel changes in the landscape (fragmentation, oldfields, fire exclusion, etc.); and climate change (driven by the increase in greenhouse gases). From [3].

 

References

[1] Moritz et al. 2005. Wildfires, complexity, and highly optimized tolerance. P Natl Acad Sci USA 102: 17912–17.

[2] Bradstock RA. 2010. A biogeographic model of fire regimes in Australia: current and future implications. Global Ecol Biogeogr 19: 145–58.

[3] Pausas JG & Keeley JE 2021. Wildfires and global change. Front Ecol Environ. [doi | web | pdf]

Entrevista

May 11th, 2021 No comments

Aquí una entrevista en la que explico es qué trabajamos, y claro, hablo de incendios forestales, biodiversidad, desertificación, la estrategia de biodiversidad de la Comisión Europea, etc.

Y a continuación otra entrevista realizada en motivo de la MedNight TV del 24 Septiembre 2021

Serotiny and WWI memorials

April 27th, 2021 No comments

On ANZAC Day (25 April; the national day of Australia, see wikipedia) I received the following query from an Australian colleague.

Apparently one of the few Australian soldiers that survived the Gallipoli battle (Turkey, 1915, WWI) picked up a pine cone (from a ‘Lone pine’), and took it back to Australia. The cone was kept on a shelf until 1933 when a horticulturalist extracted 5 seeds and germinated them. The seedlings were planted in botanic gardens; the 78-year-old trees now have special symbolic value to war veterans and the like (Fig. 1). The returned veterans are often referred to as ‘lone pine soldiers’ (and the battle, as the battle of the lone pine). My colleague asked me if the cone story had some credibility, for instance, would a pine seed germinate after 18 years?

Fig. 1. Plaque at the foot of pine tree in Kings Park, Perth, Western Australia. From [4]

The plaque in Kings Park (Fig. 1) suggest that the pine is a Pinus halepensis (Aleppo pine). However, the pines in Gallipoli peninsula (and in most Turkey) are of another species: Pinus brutia (Turkish Red Pine) [2]; the two species are very close related. So the cone that the soldier pick up should be a P. brutia, unless there was a plantation of P. halepensis there.

Pine seed, once there are out of the cone, do not last for long (mostly less than a year). However one of the characteristics of both P. halepensis and P. brutia is that they have some serotinous cones (the serotiny level is higher in P. halepensis than P. brutia, but both have a proportion of serotinous cones) [2,3]. Serotinous cones are those that remain closed after maturation, i.e., more than a year [1]. They accumulate for several years, forming a canopy seed bank; these cones open after the tree burns in a wildfire, and thus it is an adaptation to regenerate after fire [1]. At least in the case of P. halepensis, we have evidence that cones remaining close on the tree for many years; most cones open in less than 8 years, but some can last more than 15 years (Fig. 2). In addition we have evidence of cones remaining closed after harvest (at lest 12 years in my experience). This information is for P. halepensis, but could apply to P. brutia as well.

Fig. 2. Left: Frequency distribution of trees in relation to their maximum closed cone age for Pinus halepensis in eastern Spain. The gray pattern corresponds to the proportion of trees in population under high frequency of crown fires, the white to the proportion of trees where crown fires are rare. From [3]. Right: example of long-lived serotinous cones in P. halepensis in eastern Spain.

In conclusion, the Australian soldier may have picked up a serotinous cone, perhaps from a P. brutia. The seed were in the cone for 18 years and then extracted and planted. There are other accounts suggesting that several Australian soldiers took cones of both P. brutia, and P. halepensis (it’s difficult to understand why soldiers would collect pine cones after such a deadly battle, but this is another question …).

Currently most WWI memorials in Australia include a P. halepensis tree, a few a P. brutia. In the memorial cemetery near Gallipoli they planted (in the 1920s) a different pine, a Pinus pinea (stone pine, not native from Turkey, but from Italy and Spain). And in New Zealand (they shared with Australians the Gallipoli drama), the tree in ANZAC memorials includes Pinus radiata (from California) and Pinus canariensis (from Canary Islands, west Africa). That is, any of the ca. 120 pine species may do for a war memorial…

If Gallipoli has not been a fire-prone ecosystem, the pines would not be serotinous, the cones collected by the soldiers would not had kept the seeds, and we would not have pines in the Australian and New Zealand war memorials. So now, when you see a pine in a war memorial, just think about fire adaptations!

References

[1] 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. Plant Sci. 39:140-172. [doi | pdf | suppl.]  

[2] Pinus brutia jgpausas.blogs.uv.es/2017/04/19/

[3] Hernández-Serrano A., Verdú M., González-Martínez S.C., Pausas J.G. 2013. Fire structures pine serotiny at different scales. Amer. J. Bot. 100: 2349-2356. [doi | amjbot | pdf | supp.]  

[4] For more about the lone pine puzzle see: Underwood R. 2014  quadrant.org.au | wikipedia

More on serotiny|

 

Lizards smell wildfires

March 31st, 2021 No comments

The evolutionary role of fire in animals has been poorly explored [1]. We recently conducted an experiment with the mediterranean lizard Psammodromus algirus to evaluate a possible adaptive response to fire [2]. Specifically we tested whether detecting a fire by smoke is adaptive for lizards living in fire-prone ecosystems. To do so we collected lizards from habitats with contrasted fire regimes (fire-prone shrublands vs. non-fire-prone dunes) and exposed them to smoke and to a false smoke (control) in a terrarium. We video-recorded the behavioral reaction to the treatments, and determined whether each individual detected the smoke and the intensity of the reaction. We found that in populations from fire-prone habitats, more lizards reacted to smoke, and their behavioral response was more intense than in lizard populations from non-fire-prone habitats. Our results suggest that the enhanced response to smoke may have been selected as adaptive behavior in fire-prone habitats to increase survival. Smoke has been considered a very important cue for enhancing germination in plants [3]; now we show that is also a cue for fire avoidance in animals. To our knowledge, this is the first evidence of smoke detection by reptiles in wild populations. 

Lizards’ behavioral response (seconds of activity in one minute) to the treatments (Control or Smoke) and habitat (Fire-prone or Non Fire-prone). Predicted values (filled symbols with confidence intervals) and data (light colored symbols). Species: Psammodromus algirus. From [2].

References

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

[2] Álvarez-Ruiz L, Belliure J, Pausas JG. 2021. Fire-driven behavioral response to smoke in a Mediterranean lizard. Behavioral Ecol. [doi |oup | data:dryad | pdf]  [ver también: ¿Cómo sobreviven los animales a los incendios?]

[3] Keeley & Pausas 2018. Evolution of ‘smoke’ induced seed germination in pyroendemic plants. S. Afr. J. Bot. 115: 251-255. [doi | pdf];  Moreira & Pausas 2018. Shedding light through the smoke on the germination of Mediterranean Basin flora. S. Afr. J. Bot. 115: 244-250. [doi | pdf];  Tormo et al. 2014. Field evidence of smoke-stimulated seedling emergence and establishment in Mediterranean Basin flora. J. Veget. Sci. 25: 771-777. [doi| pdf];  Moreira et al. 2010. Disentangling the role of heat and smoke as germination cues in Mediterranean Basin flora. Ann. Bot. 105: 627-635. [pdf | doi]

 

A message from grasses

February 21st, 2021 No comments

This video provides a powerful message from grasses to the world, written and narrated by William Bond: The Untold Story of Grasses.

Grasses created an open sunlit world, rich in plants and animals.

When you support a tree planting project … Stop. Think. Are the trees restoring a forest? Or are they destroying an ancient grassland? What might be lost?

Further readings

  • Bond WJ. 2019. Open Ecosystems: Ecology and Evolution Beyond the Forest Edge. Oxford University Press.
  • Pausas JG. & Bond WJ. 2019. Humboldt and the reinvention of nature. J. Ecol. 107: 1031-1037. [doi | jecol blog | pdf]
  • Pausas JG. & Bond WJ. 2020. Alternative biome states in terrestrial ecosystems. Trends Plant Sci. 25: 250-263. [doi | sciencedirect | cell | pdf]
  • Afforestation is not a solution to mitigate CO2 emissions [link]
  • Mythbusting forests, by WJ Bond [link]
  • https://openecosystems.co.za/

Pinus yunnanesis

January 16th, 2021 2 comments

In the Yunnan Province of China, P. yunnanensis occurs in two growth forms: as a tree (var. yunnanensis) and as a shrub (var. pygmea) [1]. The shrubby form occurs mainly in upper slopes and ridges (Fig. 1), where soils are poor and dry, and fires are likely. This shrubby pine is very interesting and quite unique among pines: it has serotinous cones (Fig. 2), and resprouts after fire from basal buds (Fig. 3), generating multi-stemmed shrubby pine populations [1]. Serotiny is common among pines [2] while resprouting is not [3], so pines with both serotiny and resprouting are rare; and having a multi-stemmed growth form is even rarer.

Fig. 1. Pine shrubland (Pinus yunnanensis var. pygmea) in Yunnan, China. Photo C. Luo [1]
Fig. 2. Pinus yunnanensis var. pygmea showing serotinous cones, Yunnan, China. Photo: W.-H. Su [1]
Fig. 3. Pinus yunnanensis var. pygmea resprouting from basal buds after a fire, Yunnan, China. Photo: JG Pausas [1]

References

[1] Pausas JG, Su W-H, Luo C, & Shen Z. 2021. A shrubby resprouting pine with serotinous cones endemic to Southwest China. Ecology [doi | pdf]

[2] 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.]

[3] Pausas, J.G. 2015. Evolutionary fire ecology: lessons learned from pines. Trends Pl. Sci. 20: 318-324. [doi | sciencedirect | cell | pdf]

Wildfires in art: paintings II

December 31st, 2020 1 comment

I’m compiling paintings about wildfires and burned landscapes. Here some examples (click the picture to enlarge it). More examples are welcome! (email), thanks!

The painters

George Catlin (1796–1872, USA)
Fred Williams (1927–1982, Australia)
Cota Marqués (Spain): painted during the lockdown  2020
Philip Juras (Southeast USA)
Donald Ramsay (Australia)
Josep Serra Tarragón (Spain)

More at: Paintings of wildfires and burned landscapes | Wildfires in art: paintings I

     

Fire and biodiversity in the Anthropocene

November 20th, 2020 No comments

Conservation of Earth’s biological diversity will be achieved only by recognition of the critical role of fire in shaping ecosystems.

Article:

Kelly LT, Giljohann KM, Duane A, Aquilué N, Archibald S, Batllori E, Bennett AF, Buckland ST, Canelles Q, Clarke MF, Fortin M-J, Hermoso V, Herrando S, Keane RE, Lake FK, McCarthy MA, Ordóñez AM, Parr CL, Pausas JG, Penman TD, Regos A, Rumpff L, Santos JL, Smith AL, Syphard AD, Tingley MW, Brotons L. 2020. Fire and biodiversity in the Anthropocene. Science 370 (6519): eabb0355. [doi | science | pdf | suppl.]

Pine serotiny

November 14th, 2020 No comments

Some days ago I asked this question on Twitter.

What is the difference between the top and bottom pine cones in this photo? This is a question I often ask to my new students in the first field trip; in this case, Beniardà fire, 2020 [link]

These cones are from Pinus halepensis and were collected after a wildfire in Beniardà (Alicante, E Spain; burned in Aug 2020).

Many of you reply correctly; here is the full answer:

Top cones: before the fire, they were open on on the tree, i.e., without seeds. Fire burn them, and so they are all black

Bottom cones (see also the picture below): before the fire they were closed (serotinous cones), and fire opened them facilitating seed dispersal. Note that they are unburned inside. These cones contribute to the postfire regeneration of the pine.

Serotinous cones in Pinus halepensis: before (left) and after a fire (right)

 

References

  • 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 Reviews Plant Sci 39:140-172. [doi | pdf | suppl.]
  • Pausas JG. 2015. Evolutionary fire ecology: lessons learned from pines. Trends Plant Sci 20: 318-324. [doi | sciencedirect | cell | pdf]
  • Castellanos MC, González-Martínez S. & Pausas JG. 2015. Field heritability of a plant adaptation to fire in heterogeneous landscapes. Mol Ecol 24: 5633-5642. [doi | pdf | suppl.]
  • Hernández-Serrano A, Verdú M, González-Martínez SC, Pausas JG. 2013. Fire structures pine serotiny at different scales. Am J Bot 100: 2349-2356. [doi | amjbot | pdf | supp.]
  • Hernández-Serrano A, Verdú M, Santos-Del-Blanco L, Climent J, González-Martínez SC & Pausas JG. 2014. Heritability and quantitative genetic divergence of serotiny, a fire-persistence plant trait. Ann Bot 114: 571-577. [doi | pdf | suppl.]

 

More on serotiny: Serotiny: a review | Pinus brutia | Heritability of serotiny | Heritability of serotiny (2) | Evolutionary fire ecology in plants | Serotiny |

Cork oaks in Murcia

November 1st, 2020 No comments

Cork oak (Quercus suber) typically grows in relatively wet mediterranean environments [1]. However there are some cork oaks in arid climate; perhaps the population in the driest site is the small and isolated cork oak patch in Rambla de Talón (ca. 100 m asl, Ribera de Molina, Molina de Segura, Murcia, Spain; Fig. 1). It includes less than 100 individuals scattered in an area of sandy conglomerates (Fig. 3); the average rainfall is less than 300 mm. They are believed to have been planted in the past (when?), but their persistence in such arid conditions gives them a high added value. This population is much smaller and is located in a much drier conditions than the one in Pinet (Valencia) we mentioned some time ago [2,3].

Figure 1. Distribution of Cork oak (Quercus suber) in the Iberian Peninsula. Light grey is the species distribution; dark grey is the data from forest inventories; crosses are small isolated populations. In red is the population of Murcia. Map from [1].

Precipitation during the last spring was above average, and currently (end of October 2020) most oaks in Rambla de Talón look healthy and have some acorns. Of the 26 tree we look at, the number of acorns ranged from 0 (7 trees) to more than 400 acorns (2 trees), but most trees have less than 10 acorns (Fig. 2; median= 5 acorns). In addition, there is no evidence of recruitment from previous years. That is, if persistence of this population is desired, it would require some help for their regeneration. Given that they produce some acorns, restoration actions using local acorns is possible.

Fig. 2 Acorn production (October 2020) in 26 cork oak trees from Rambla de Talón, Ribera de Molina, Murcia.

References
[1] Aronson J, Pereira JS, Pausas JG (eds). 2009. Cork Oak Woodlands on the Edge: conservation, adaptive management, and restoration. Island Press, Washington DC. 315 pp. [The book]

[2] Pausas JG, Ribeiro E, Dias SG, Pons J & Beseler C. 2006. Regeneration of a marginal Cork oak (Quercus suber) forest in the eastern Iberian Peninsula. J. Veget. Sci. 17: 729-738. [pdf | doi | wiley ]

[3] El surar de Pinet – a small isolated population of cork oak. jgpausas.blogs.uv.es/2018/10/15/



Hummingbirds and wildfires

October 6th, 2020 No comments

Hummingbirds are among the most iconic birds of America, especially abundant in the tropics. They are very important pollinators (nectar feeders), thus their abundance and distribution are likely to affect hummingbird-pollinated plants, many of which are endemic or endangered. A recent review in western United States [1] suggests that most hummingbird species respond positively to wild or prescribed fire and thus, for the conservation of these emblematic birds, it is important to promote landscape mosaics, with early and mid postfire successional habitats, together with forest patches.

Here is a video by Contreras-Martínez et al. on hummingbirds and wildfires in Sierra de Manantlán Biosphere Reserve, Mexico [2]. The video is in Spanish; hummingbirds are ‘colibríes’ or ‘picaflores’

Grandes Guerreros: Colibríes y Fuego

Créditos del vídeo:
Filmación y Edición: Carlos Armando Pacheco Contreras (Vidacinema)
Productor: Sarahy Contreras Martínez
Guión: Sarahy Contreras Martínez, Carlos Armando Pacheco Contreras & Oscar Cárdenas Hernández
Narración: Cesar Híjar Tejada
Investigación Científica: Sarahy Contreras Martínez (Colibríes) & Enrique Jardel Peláez (Fuego)
Música Original: Erick Ríos Vázquez
Mezcla de audio: Sognare Estudios
Also available at: https://www.facebook.com/watch/?v=869506306897201

References
[1] Alexander JD, Williams EJ, Gillespie CR, Contreras-Martínez S & Finch DM. 2020. Effects of restoration and fire on habitats and populations of western hummingbirds: A literature review. Gen. Tech. Rep. RMRS-GTR-408. Fort Collins, CO, USDA, https://www.fs.usda.gov/treesearch/pubs/59664

[2] Pausas JG 2016. Flammable Mexico. Internat. J. Wildland Fire 25: 711-713. [doi | pdf ]

[3] Other related videos: Burning for biodiversity | Fire & the Florida scrub | La huella del fuegoFish & fire

[4] Other post on fire & fauna | fire & pollination | fire & Mexico |

by Josep Serra, 2021

Pyrocumulonimbus and firestorms

September 30th, 2020 No comments

Meteorologists call Cumulus (Cu) to cotton-like clouds, and Cumulonimbus (Cb) to denser and bigger clouds carried by powerful upward air currents. When these clouds are originated by a fire (or a volcano), we call them pyrocumulus (PyroCu) and pyrocumulonimbus (PyroCb) clouds.

Pyrocumuloninbus (= Cumulonimbus flammagenitus) are dense towering vertical clouds carried by powerful upward air currents generated by the heat of a wildfire [1]. These fires are also called plume-dominated fires, super-heated wildfires, or wildfire-driven thunderstorms. The origin is typically tied to very high and continuous fuel loads and extreme fire weather that produces great heat and strong convection currents. In most cases, they remain in the troposphere, but when the heat produced by the fire is very high, they can cross the tropopause and inject a large amount of smoke into the stratosphere; in those cases, wildfires contribute to the global carbon and nutrients redistribution [2]. These plumes often collapse when temperatures drop with altitude and create extreme winds. That is, these high intensity fires generate feedback processes between the atmosphere and the fire that produce strong surface winds, tornadoes, and even pyrogenic lightning ignitions that further expand the fire (firestorms).

Firestorms are wildfires with extreme, sometimes erratic behavior, typically beyond the capability of fire services to contain; the term has been used to describe very different fire types such as wind-driven fires (e.g., Santa Ana wind firestorms in California) and pyrocumulonimbus plume fires [1].

Examples of pyrocumulonimbus clouds (click in the picture for enlarge it).

A: Benaixama fire, Alicante (Spain), 7/2019, by Servicio de Vigilancia de Prevención de Incendios Forestales, Observatori Caperutxo, Generalitat Valenciana.
B: Llutxent, Valencia (Spain), 8/2018, by Empar.
C: Tasmania (Australia), 2013, by Janice James.
D: Creek fire, California (US), 9/2020, by Thalia Dockery.
E: La Pampa (Argentina), 1/2018, Earth Observatory, NASA.
F: Funny river, Alaska (US), 5/2014, Earth Observatory, NASA.

References

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

[2] Pausas J.G. & Bond W.J. 2020. On the three major recycling pathways in terrestrial ecosystems. Trends Ecol. Evol. 35: 767-775. [doi | sciencedirect | pdf]

Mythbusting Forests

July 23rd, 2020 2 comments

Despite the multiple evidence that afforestation is not a solution for mitigating the increased atmospheric CO2 [1], there are still lobbies and multimillionaire clubs willing to plant millions of trees at the global scale, and spreading myths about the benefits of trees and large afforestation programs. Recently (17 July 2020), William Bond gave a talk at Oxford University to bust these myths. Here is his talk, and below is a summary of the top 5 myths.

Myth 1. Forest are ancient, non-forests are caused by deforestation. There is evidence of ancient species-rich grasslands and shrublands in many parts of the world (from Cerrado in Brazil, to grasslands in Africa, shrublands in Mediterranea ecosystems, etc.). In fact animal grazers evolved long ago (long before humans could deforest) in grasslands. There are also evidences of many tropical forests that were thought to be ancient and are not (e.g., youtube). This myth has deep roots in the western culture [2].

Myth 2. Oxygen comes from trees: cutting down forest will deprive us of air to breath. Oxygen is more ancient than forests! The atmospheric concentration of oxygen during much of the evolutionary history of plants, before the rise of dense tropical forests, has been higher than current level (21%). Fire requires oxygen to burn, and there has been fire since early colonization of land plants [3]. Statements like the Amazon provides 20% of our oxygen are wrong; the Amazon consume about as much O2 as it produces; O2 is ancient, it doesn’t depend on trees (see details: link1 & link2). There are lots of reasons to preserve the Amazon, but running out of oxygen isn’t one of them.

Myth 3. Forests ‘make rain’: plant trees to get more water. W. Bond note that many city dwellers and some climatologists suggest that planting trees would increase water supply, but farmers, which have daily experience with land management, says that planting trees dries up rivers. A catchment experiment in South Africa unambiguously show that catchments with tree plantations get drier compared with those under natural shrublands (Wyk 1987). Maybe some catchments, given their size, climate and topography, may generate their own rainfall (as often suggested for the Amazon), but this doesn’t seems a general rule. Planting trees will not ‘make rain’, most likely will dry out the watershed (e.g., Wang et al. 2020).

Myth 4. The biggest store of terrestrial carbon is in tropical forests. Tropical forests store about 225 Pg C, while boreal soils store ca. 1300 Pg C. So, from the C perspective, it is more important to conserve boreal soils (peatlands, etc.) than tropical forests! Obviously tropical forest need to be conserved for their biodiversiy. But you better forget about planting trees, and start thinking in conserving boreal peatlands as their destruction would release high amount of CO2 to the atmosphere. See also: Friggens et al. 2020.

Myth 5. Forests equate with biodiversity. Many tropical forests are highly diverse, but there are examples where planting trees implies a loss of biodiversity (Abreu et al. 2017, Phifer et al. 2017). When comparing savannas and forest for the same rainfall, there are no differences in biodiversity (Murphy et al. 2016). In addition, many of the global biodiversity hotspots are open non-forest ecosystems or mosaics of forest and open ecosystems. So the myth cannot be hold. In fact, landscape mosaics of forest and non-forest are highly diverse landscapes [4].

References

[1] Afforestation is not the solution to mitigate CO2, jgpausas.blogs.uv.es/2019/10/17/

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

[3] 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 | post]

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


Update: a new paper that addresses this topic:
Fleischman et al. 2020. Pitfalls of tree planting show why we need people-centered natural climate solutions. BioScience, doi: 10.1093/biosci/biaa094

Serotiny: a review

June 9th, 2020 No comments

Here is a new review paper on serotiny in plants [1]. Serotiny refers to prolonged storage of seeds in woody structures (cones or fruits) on the mother plant for several growing seasons. This implies an accumulation of a canopy seed bank with seeds from different. Serotiny confer fitness benefits in environments with frequent crown-fires, as the heat of the fires opens the woody structures and thus seeds are dispersed in the post-fire bed (where resource are abundant and competition is low). There are other ways by which some cone/fruit can be opened (e.g., dry warm winds), but the number of seeds released and the chance of successful recruitment are much lower than in postfire conditions, and thus fire provides higher fitness benefits for serotinous plants than any other cue factor. This is why most serotinous plants occurs in ecosystems with frequent crown fires. Serotiny has been studied mainly in pines [2-4] and Proteaceae, but we know at least 12 families and more than 50 genera with serotinous species [1]. And there is a diversity of serotinous structures (cones and fruits) in different genera and families (Fig. 1).

Figure 1. A) Callitris (Actinostrobus) pyramidalis (Cupressaceae); B) Postfire Cupressus sempervirens (Cupressaceae); C) Cone of Pinus patula; D) Postfire cones of Pinus radiata; E) Folicles of Hakea cyclocarpa (Proteaceae); F) Hakea stenocarpa follicle; G) Follicles of H. platysperma; H) Xylomelum angustifolium (Proteaceae) follicle; I) Lambertia echinata (Proteaceae) follicle; J) Cone of Banksia lemanniana (Proteaceae); K) B. hookeriana burning; L) Postfire B. leptophylla cone; M) Cluster of capsules of Leptospermum spinescens (Myrtaceae), inset: seeds of Callistemon (Melaleuca) teretifolius; N) Elongated cluster of sessile capsules of Callistemon citrinus (Myrtaceae), + seeds of Callistemon (Melaleuca) teretifolius; O) Woody capsules of Eucalyptus todtiana (Myrtaceae), Inset: capsules of Angophora hispida (Myrtaceae); P) Spikes of Connomois parviflora (Restionaceae); Q) Protea burchellii (Proteaceae); R) fruits of Protea burchellii; S) Cone of Allocasuarina torulosus (Casuarinaceae); T) Cone of Isopogon trilobus (Proteaceae); U) Cones of Petrophile brevifolia; V) Seedlings from serotinous H. polyanthema, B. attenuata and B. hookeriana in litter microsite. For more details see [1].

References

[1] 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. Plant Sci. [doi | pdf]

[2] Hernández-Serrano A, Verdú M, González-Martínez SC, Pausas JG. 2013. Fire structures pine serotiny at different scales. Am. J. Bot. 100: 2349-2356. [doi | amjbot | pdf | supp.]

[3] Hernández-Serrano A, Verdú M, Santos-Del-Blanco L, Climent J, González-Martínez SC, Pausas JG. 2014. Heritability and quantitative genetic divergence of serotiny, a fire-persistence plant trait. Ann. Bot. 114: 571-577. [doi | pdf | suppl.]

[4] Castellanos MC, González-Martínez S, Pausas JG. 2015. Field heritability of a plant adaptation to fire in heterogeneous landscapes. Mol. Ecol. 24, 5633-5642. [doi | pdf | suppl.]  

 

More on serotiny: Serotiny | Heritability of serotiny (1) | Heritability of serotiny (2): a molecular approach | Evolutionay fire ecology in pines 

Microbes, herbivores, and wildfires

May 4th, 2020 No comments

Plants are the largest biomass component of most terrestrial ecosystems, and litter decomposition is considered the dominant process by which nutrients return to plants. In a recent paper [1] we show that in terrestrial ecosystems, there are three major pathways by which plant biomass is degraded into forms that release nutrients again available to plants: microbial decomposition; vertebrate herbivory; and wildfires. These processes act at different spatial and temporal scales, have different niches, and generates different ecological and evolutionary feedbacks. The three processes can occur in a given ecosystem (competing for the same resource, biomass), but the relative importance of each varies with the micro- and macro-environmental conditions (see Figure below).

Wildfires and herbivory are two powerful biomass consumers; they generate feedback processes that maintain vegetation at states of lower biomass than would be expected from the physical environmental conditions (alternative vegetation states [2]). In addition, wildfires and herbivory also select for light-loving species with a set of adaptive traits to persist under these consumers [3,4]. That is, both herbivory and fire can influence the mix and attributes of plant species, while the mix and attributes of plants also influence the fire and grazing regimes. These ecological and evolutionary feedbacks make fire and herbivory distinct from other abiotic disturbances such as cyclones, landslides, avalanches, volcanoes, or floods, where plants may respond – but the disturbance will not change in response to these plant responses. That is, wildfires, herbivory, and microbial decomposition can be viewed as biotic processes that structure our ecosystems and the biosphere, at different temporal and spatial scales.

This holistic view in which microbes, herbivores, and wildfires play a joint role in the functioning of ecosystems contributes to a better understanding of the diversity of mechanisms regulating the biosphere.

Figure: Plant biomass and vegetation structure in terrestrial ecosystems are determined by three feedback processes: vertebrate herbivory (H), microbial decomposition (D), and wildfires (W). These three processes also interact with each other (e.g., competition for biomass; but positive interactions also exist). Relative importance of each of the three ecosystem pathways varies in the environmental space (niche), here defined by the water availability and soil fertility. Illustration by Dharmaberen Studio. From [1].

References

[1] Pausas J.G. & Bond W.J. 2020. On the three major recycling pathways in terrestrial ecosystems. Trends Ecol. & Evol. [doi | pdf]

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

[3] Keeley J.E., Bond W.J., Bradstock R.A., Pausas J.G. & Rundel P.W. 2012. Fire in Mediterranean Ecosystems: Ecology, Evolution and Management. Cambridge University Press. [the book]  

[4] Bond, W. J. 2019. Open Ecosystems: Ecology and Evolution Beyond the Forest Edge. Oxford University Press.

 

Megafauna history shapes plants

April 24th, 2020 No comments

The role of large herbivores in explaining broad-scale ecological pattern has probably been underestimated [1]. For instance, they are important in maintaining many landscapes and biomes across the world [2]. In a recent paper we show that the different history of megafauna abundance and extinctions in different continents has shaped the dominance of many plant traits [3]. Tropical Africa (paelotropics) and tropical South America (neotropics) are a clear example of contrasting megafauna history under similar environmental conditions. By comparing plant traits of woody species in different biomes (savannas and forests) and for the two different continents, we found that continent explain better the differences in plant traits than biome, climate, or soil, and that the differences between continents are consistent with the higher impact of large vertebrates in Africa than in South America. For instance, plants in African savannas tend to be more thorny and to have higher wood density, i.e., traits related to defense against megaherbivores. In contrast, South American savannas (Cerrado) harbor more species with underground bud banks (geoxyles [4]), and thicker protective barks, i.e., traits related to protect from wildfires [4,5].

Megafauna was certainly present in South America before the Holocene overkilling by humans, however, it is unlikely they live in the brazilian savannas (cerrado); their weak and vulnerable stems (low height growth, low wood density, and lack of spines), are unlikely to have evolved in regions with abundant browsers. We hypotheses that megafauna in South America was distributed in: 1) an open version of the current seasonally dry tropical forests (SDTF, e.g., Chaco) as the proportion of thorny species is similar to African savannas (and much higher than the cerrado); and 2) the subtropical grasslands, as they currently need to be maintained by humans due to the missing megaherbivores (landscape anachronism [1]).

Overall our results suggest that variation in plant traits in the tropics is unlikely to be fully understood without considering historical factors, especially the direct and indirect impacts of megafauna. Looking at plants and thinking on their megafauna history may provide novel insights for understanding vegetation patterns across the globe [1].

The effects of megafauna history (left: absence, right: present of megafauna) on plant functional traits of tropical woody species in different biomes (savannas and forests). Arrows between the dominant driver(s) (boxes) and traits (circles) indicate positive (blue) and negative (red) effects. From [3]

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

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

[4] 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]

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

Torre de l’Espanyol postfire

March 16th, 2020 No comments

On June 26, 2019 a wildfire started in Torre de l’Espanyol (Ribera de l’Ebre, Tarragona, Catalonia, Spain) and burned ca. 5000 ha. I recently visited the area (8.5 months postfire); the regeneration was still relatively low, as the winter has been quite dry, but many species were resprouting and some seedlings were starting to emerge. Here are some of the plants that were flowering: Platycapnos (Fumaria) cf. spicata, Muscari neglectum ssp. atlanticum, Fritillaria lusitanica (=F. boissieri, F. pyrenaica ssp. hispanica), Ophrys lupercalis (=O. forestieri; O. bilunulata was also flowering but not pictured below).

 

More on postfire flowering: jgpausas.blogs.uv.es/2018/11/22/

Paleofuegos: del Silúrico a la actualidad

February 18th, 2020 1 comment

En los últimos años hemos aprendido mucho sobre ecología y evolución de las plantas en relación a los incendios forestales [1]. Una de los puntos clave pare ello fue encontrar evidencias de que siembre, a lo largo de toda la historia evolutiva de las plantas, han habido incendios, incluyendo en las primeras comunidades vegetales que colonizaron el medio terrestre [2]. Y todo esto se sabe gracias a los avances en el estudio de los carbones fósiles. Uno de los estudiosos más importantes en paleo-fuegos es el geólogo Andrew Scott, quien ha dedicado gran parte de su vida a mirar carbones fósiles, y que en 2018 resumió sus investigaciones en un libro titulado Burning Planet: The story of fire through time [3]. Ahora tenemos la suerte de que ese libro se ha traducido al castellano, Planeta en llamas: la historia del fuego a través del tiempo (Galaxia Gutenberg, 2020). Creo que este libro es un buen complemento a mi libro sobre la ecología de los incendios forestales [4], y espero que ayude a la comunidad hispánica a entender mejor el papel ecológico, evolutivo, y ancestral que tiene el fuego en nuestros ecosistemas.

Referencias

[1] Ecology & Evolution in fire-prone ecosystems [enlace]

[2] 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 | post | pdf]

[3] Scott A. 2018. Burning Planet: The story of fire through time. Oxford University Press. [versión española: Planeta en llamas: la historia del fuego a través del tiempo. Galaxia Gutenberg, 2020]

[4] Incendios forestales, una visión desde la ecología, CSIC-Catarata, 2012 [enlace]

Australian fires 2019/20

January 12th, 2020 No comments

Australia is a very flammable continent, and fires have been occurring there for millions of years. As a consequence, many plants and animals have developed adaptations and strategies to cope with recurrent fires. However, the current fire season in eastern Australia is really very severe, including not only very large fires but also high intensity firestorms. SE Australia has suffered other sever fire seasons in the past (an iconic example is the Black Friday bushfires in 1939). Why is this happening now? Here I’ve compiled key figures that help us to understand it.

In the last few years, Australia has been suffering an increase in temperature; on average, each year is hotter than the previous year (Fig. 1). In fact, 2019 was the warmest years, but also the driest year (with the lowest rainfall) ever recorded. December 2019, when most fires started, was climatically an extreme (Fig. 2). During the December heatwave (Fig. 3) some meteorological station (e.g., Penrith, near Sydney) recorded temperatures over 48oC, and the record of highest average maximum temperature for Australia was broken on two consecutive days (40.7 and 41.9oC  on 17 and 18 Dec, respectively). January 4 was Canberra’s hottest day since records began (44oC). In such extreme weather conditions, ignitions easily become a wildfire (in fact, several of the wildfires started from a dry lightning), and fires spread very quickly in a vegetation that has been in a drought for many months. This generates not only huge areas burned (Fig. 4), but also very hot fires and strong uplift air columns that reach the stratosphere (pyrocumulonimbus). These are called firestorms. Firestorms produce there own winds and spread embers and the fire very fast; they even produce lightnings that generate additional wildfires. Firestorms produce extreme fire behaviour that is beyond the capacity of firefighters. In those fires, as it happens in volcanoes, the smoke reaches the stratosphere and circulates at very long distances (e.g., currently smoke from these fires has already reached South America).

The fire season has not ended yet. The ecological effects of these fires will depend on many factors (spatial variability of fire intensity, previous fires, species, etc…). The size and intensity of these fires suggest that they can have some negative consequences, but it is too early for any quantitative evaluation. Many plants are starting to resprout just few days after the fire, even under those drought conditions; some animals are leaving their hiding places, exploring the burned area, and carcasses are locally abundant suggesting patches of high animal mortality. We’ll see when will the rain come, and how plants and animals will respond. For humans, the consequences are catastrophic (fatalities, destruction of many infrastructures, smoke problems, etc.).

Fig. 1. In Australia, each year is hotter than the previous year, on average. From Australian Bureau of Meteorology
Fig. 2. December 2019 was climatically an extreme, unprecedented in relation to rainfall and temperature. Elaborated with data from Australian Bureau of Meteorology
Fig. 3. Global temperature in December 18th, 2019, as shown by Windy. Note also that part of the differences in temperature are due to the different time zones; i.e., middle of the day in Australia, night time in South America, and early morning in Africa.
Fig. 4. Major fires in south-east Australia by January 10th, 2020 (5,634,000 ha). From @eforestal [update Jan 18th: 6 millions ha]

More information:

Australian Bureau of Meteorology  | @eforestal maphub  | NSW fire service | VIC emergency | Desinformation |

Update (4/2020): For a map of the time-since-fire and fire severity across NSW fires, see: Bradstock et al. 2020, Global Change Biol., doi:10.1111/gcb.15111 (spoiler: most fires burned at relatively low severity!)

Alternative Biome States

January 8th, 2020 No comments

There is growing interest in the application of alternative stable state (ASS) theory to explain major vegetation patterns in tropical ecosystems [1] and beyond [2]. In a recent paper [3] we introduced the theory as applied to the puzzle of non-forested (open) biomes growing in climates that are warm and wet enough to support forests (alternative biome states, ABSs; Fig. 1). Long thought to be the product of deforestation, diverse lines of evidence indicate that many open ecosystems are ancient. They have also been characterized as ‘early successional’ even where they persist for millennia. ABS is an alternative framework to that of climate determinism and succession (Table 1 below) for exploring forest/nonforest mosaics. Within climatic and edaphic constraints, consumers (fire and herbivores) can produce vastly different ecosystems from the climate potential and have done so for millions of years [4]. This framework explains not only tropical forest–savanna landscapes, but also other landscape mosaics across the globe (Fig. 2).

Fig. 1. Generalized feedback processes in fire-prone landscapes where open and closed biomes (e.g., a grassland and forest) are alternative stable states maintained by stabilizing feedbacks, while perturbations generate abrupt transitions among states (destabilizing factors). From: [3].

Fig. 2. Examples of multibiome landscape mosaics where closed forests alternate with open biomes (grasslands) that are maintained by mammal herbivory and fire. From: [3].

Table 1. Comparison of the three main dynamic processes assembling disturbance-prone communities and landscapes: classical (facilitation) succession, autosuccession, and ABS. From: [3].

References

[1] Dantas V.L., Hirota M., Oliveira R.S., Pausas J.G. 2016. Disturbance maintains alternative biome states. Ecol. Lett. 19: 12-19. [doi | wiley | pdf | suppl.]

[2] Pausas, J.G. 2015. Alternative fire-driven vegetation states. J. Veget. Sci. 26:4-6. [doi | pdf | suppl.]

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

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

Diversidad política (4)

January 7th, 2020 No comments

España es un país muy diverso, con una gran variedad de climas, paisajes, comidas, bailes, lenguas, hablas, etc.; una diversidad generada por su peculiar situación geográfica, su heterogeneidad topográfica y la variedad de acontecimientos ocurridos a lo largo de su historia. Esto ha conferido a la población una elevada diversidad cultural, de ideas y puntos de vista. Sólo un gobierno plural y diverso, capaz de aceptar las diferencias, podrá gestionar correctamente y preservar la diversidad de este país. El bipartidismo difícilmente puede representar la diversidad española.

En la figura (abajo) vemos la evolución de la diversidad política en España, calculado a partir la distribución de los escaños de los diferentes partidos (en azul), para todas las Elecciones Generales al Congreso realizadas durante la democracia. El 15M (mayo 2011) sirvió para revitalizar la diversidad política del Congreso, tras muchos años de decaimiento (ver figura, en azul).

Tras las últimas elecciones generales en noviembre de 2019, en España tenemos un Congreso con la mayor diversidad de ideas políticas de la historia de la democracia (ver figura, linea azul); y esperamos que sea capaz de gestionar bien la diversidad del país. La diversidad del Congreso es prácticamente la misma que después de las elecciones de abril de 2019 (como era esperable), y sin embargo, ese Congreso fue incapaz de gestionar esa diversidad, seguramente por la falta de experiencia democrática, es decir, falta de capacidad de diálogo, de capacidad para aceptar las diferentes opiniones, y de excesivo deseo de poder de los lideres. Esperemos que el nuevo Congreso, y el nuevo gobierno que ahora empieza, hayan aprendido la lección.

Cabe señalar que la diversidad de opciones políticas de los votantes españoles, calculadas a partir de los votos y las abstenciones (linea roja de la figura) es más elevada que la diversidad política que se refleja en el Congreso (escaños; linea azul). El sistema electoral español hace que se pierda un parte nada desdeñable de la diversidad política de los ciudadanos. Con la llegada del 15M se ha visto reducida esa pérdida de diversidad (la linea azul se acerca más a la roja). Aproximadamente el 30% de los censados decidieron no contribuir a confeccionar la composición del Congreso (abstenciones, votos en blanco, votos nulos), y por lo tanto, contribuyen a esa pérdida de diversidad en el Congreso. La figura también refleja que pequeños cambios de opinión en los votantes a lo largo del tiempo (linea roja) se reflejan de manera amplificada en el Congreso (linea azul).

Figura: Valores de diversidad política (expresada con el índice de diversidad de Shannon-Weaver) calculado a partir de las opciones de los votantes (incluye votos a partidos, blancos, nulos y abstención; en rojo) y calculado según la distribución de los escaños resultantes (azul), para cada una de las Elecciones Generales al Congreso (España) realizadas durante la democracia (elaborado a partir de la base histórica de resultados electorales del Ministerio del Interior).

Entradas relacionadas

Diversidad política (3): jgpausas.blogs.uv.es/2016/07/02/
Diversidad política (2): jgpausas.blogs.uv.es/2015/12/30/
Pérdida de diversidad política en España: jgpausas.blogs.uv.es/2008/03/11/ 
Carta a los no votantes: votar suma la abstención resta: jgpausas.blogs.uv.es/2019/04/13/

Nota aclaratoria: en las entradas previas sobre diversidad política en este blog, la diversidad política de los votantes (linea en rojo) se calculaba en base a la distribución de los votos a los distintos partidos. En esta entrada, y par reflejar un poco mejor la diversidad de las personas con derecho a voto, se ha calculado no sólo en base a los votos a los partidos, sino también incluyendo los votos en blanco, los nulos y las abstenciones.

Wildfires in art: paintings

December 22nd, 2019 2 comments

I’m compiling paintings about wildfires and burned landscapes. Here some examples (click the picture to enlarge it). I would appreciate additional examples (email), thanks!

The painters

George Catlin (1796–1872, USA)
Eugene von Guerard (1811–1901, Austria, Australia)
Vasily Polenov (1844–1927, Russia)
Tom J. Thomson (1877–1917, Canada)
Charles E. Burchfield (1893–1967, USA)
Fred Williams (1927–1982, Australia)
Rick Amor (1948-, Australia)
Donald Ramsay (Australia)
Josep Serra Tarragón (Spain)

More at: Paintings of wildfires and burned landscapes

Wildfires in southern Chile

November 29th, 2019 No comments

Ecosystems in southern Chile are not considered among the typical fire-prone ecosystems such as tropical savannas or mediterranean ecosystems. However, natural wildfires do occur (and has occurred since long ago), during drought periods, and are part of the ecological processes of the region. Here are some examples I have just visited.

Fitzroya cupressoides (alerce in Spanish, lahuán or lawal in Mapuche) is a shade-intolerant long-lived conifer native to the Andes of southern Chile and Argentina. Fitzroya is a monotypic genus in the cypress family. It often coexist with shade-tolerant species of Nothofagus (e.g., N. nitida). The bark of Fitzroya is relatively thick, and postfire tree survival depends on the intensity of fire; fire intensity in these ecosystems is typically patchy and some trees, especially large trees, do survive (Fig. 1 below and [1]). In fact, wildfires remove the shade-tolerant trees and open the space for Fitzroya which regenerates vegetatively (from root suckers) or from seeds coming from the surviving trees. Without wildfires, it would be hard for Fitzroya to compete with shade-tolerant broad-leaved trees.

Fig. 1. Dead and surviving Fitzroya cupressoides trees after fire in Parque Nacional Alerce Costero, Chile

Araucaria araucana (araucaria) is a conifer, considered a living fossil, native to central and southern Chile and western Argentina. It is a non-flammable tree (sensu [2]) because it typically self-prune their lower branches, the crown is quite open, it has a thick bark, and their foliage is hard and difficult to burn. This very low flammability allows Araucaria to survive even in flammable environments [2]. For instance, it occurs in shrublands of Nothofagus antartica (ñirre; see Fig. 2 below); this Nothofagus is a flammable multi-stemmed shrub that has a strong basal resprouting ability. This shrubland burn with some frequency but most Araucaria tree do not get burnt (fire can leave some scars in the trunk, see Fig. 3 below and dendroecological analysis in [3]). Araucaria araucana also growth in dens forests either as dominant tree or with other trees such as Nothofagus pumilo (lenga); such forest rarely burn and the regeneration of araucaria is based on gap dynamics. In fact, the two ecosystems (the shrublands of N. antartica, and the forests of N. pumilo) are an example of alternative biome states [4,5].

Fig. 2. Araucaria araucana growing in a shurbland of Nothofagus antartica (ñirre) in the foothills of the Lanín volcano, Chile
Fig. 3. Fire scars in three araucaria alive trees in the foothills of the Lanín volcano, Chile

References

[1] Lara A, Fraver S, Aravena JC & Wolodarsky-Franke A. 1999. Fire and the dynamics of Fitzroya cupressoides (alerce) forests of Chile’s Cordillera Pelada. Ecoscience, 6, 100-109.

[2] Pausas JG, Keeley JE, Schwilk DW. 2017. Flammability as an ecological and evolutionary driver. J. Ecol. 105: 289-297. [doi | wiley | pdf]
[post-1 | post-2]

[3] González ME, Veblen TT & Sibold JS. 2005. Fire history of Araucaria–Nothofagus forests in Villarrica National Park, Chile. J. Biogeogr. 32:1187-1202.

[4] Pausas JG. 2015. Alternative fire-driven vegetation states. J. Veget. Sci. 26:4-6. [doi | pdf | suppl.]

[5] Pausas JG & Bond WJ. 2020. Alternative biome states in terrestrial ecosystems. Trend Plant Sci. [postprint]

 

Afforestation is not a solution to mitigate CO2 emissions

October 17th, 2019 No comments

“I cannot think of a more tasteless undertaking than to plant trees in a naturally treeless area, and to impose an interpretation of natural beauty on a great landscape that is charged with beauty and wonder, and the excellence of eternity.” – Ansel Adams

 

Some scientific articles and many newspapers and magazines have spread the idea that planting many trees would be one of the best and most natural ways to fight against climate change. This is because trees fix CO2 through photosynthesis and thus they could lower the atmospheric CO2 concentration. To revert the current CO2 levels, if possible at all, would require the tree plantation to be massive and global. However there is increasing evidence that a massive afforestation is not a solution for mitigating CO2 emissions, and in fact, it could be detrimental, especially in a warming world. Here are the main reasons:

  • Planting trees in grasslands, savannas, shrublands and other open ecosystems (those potential for massive afforestation) would imply a large loss of biodiversity. Many of these environments are ancient, with many endemics to open ecosystems, i.e., species that are shade-intolerant o require large open spaces [1].
  • Potential carbon fixation by afforestation, as estimated by those advocating for massive tree plantations, is largely overestimated. For instance, they often assume that treeless ecosystems do not store C, while many of these ecosystems store a lot of C below-ground (savannas, shrublands, peatlands, …). They also neglect that forest in boreal and high mountain environments absorb more sunlight (reduce albedo) and emit more heat than treeless ecosystems (especially when snowy), and thus they exacerbate global warning. Similarly massive afforestation in arid ecosystems could also reduce albedo (increase darkness). After accounting for all these and other details [2-5], the potential C fixation estimates by afforestation become much lower than previously thought.
  • There are physiological limits to increase ecosystem photosynthesis, and the increase is very slow (compared with the anthropogenic CO2 release). Any increase would require huge amount of water and the concomitant increase in respiration [6].
  • Many of the potential sites for afforestation are in dry seasonal climate, and thus prone to fire, if fuel is available. Massive afforestation would increase the amount and continuity of fuels (landscape homogeneization), increasing the chance of large and intense fires (i.e., abruptly releasing large amounts of CO2); this is already happening with other afforested areas (e.g., 2017 fires in Portugal and Chile [7]). They would also be prone to diseases and insect outbreaks, especially given the ongoing warming.
  • Massive afforestation would reduce land availability for agriculture and grazing; it would also consume a lot of water [8]. All this would trigger a number of socio-economic impacts (e.g., rural depopulation), especially in poor countries.
  • Massive afforestation would be very expensive, yet would not make much C fixation during the next two or three decades (small trees don’t store much C). For C fixation it would be more efficient (and sustainable) to stop deforestation (i.e., to conserve mature forests with trees that are currently fixing C [9]), i.e., to pay subsides to owners or countries for conservation (e.g., Amazon, Indonesia, etc.).

There is no scientific evidence to support massive afforestation to fight against climate change. And we should not get distracted from the urgent actions needed: to drastic reduce fossil fuel use, to invest in alternative energy sources, to stop deforestation and ecosystem destruction, and to restore natural ecosystems.

Note that this message is not against tree plantations per se (e.g., for wood, food, fiber, for improving urban quality, etc.), but to emphasize that all the evidence points against massive afforestation as part of the solution for CO2 mitigation. For instance, planting trees in urban areas would contribute little to CO2 fixation, but have many other benefits, such as reducing the urban heat effect, filtering pollution, improving urban biodiversity and mental health for people, and even reducing the local climate change [10].

Left: species poor afforestation in southern Bulgaria; it burned with a high intensity fire 50 years after plantation (the Kresna fire, 2017). Right: species rich forest-savanna mosaic with frequent natural low intensity fires. Photos: JG Pausas, WJ Bond (from [11])

References

[1] Bond et al. 2019. The trouble with trees: Afforestation plans for Africa. Trends Ecol. Evol. doi:10.1016/j.tree.2019.08.003

[2] Veldman et al. 2019. On “The global tree restoration potential”. Science 366 (6463) 18 Oct 2019 [doi | link] + see also in the same issue: Lewis et al. [link], Friedlingstein et al. 2019 [link], Luedeling et al. [link], Delzeit et al. [link]

[3] Krause et al. 2019. Pitfalls in estimating the global carbon removal via forest expansion. bioRxiv 788026.

[4] Taylor SD & Marconi S. 2019. Rethinking global carbon storage potential of trees. bioRxiv 730325.

[5] Rahmstorf S. 2019. Can planting trees save our climate? RealClimate http://www.realclimate.org/index.php/archives/2019/07/can-planting-trees-save-our-climate/

[6] Baldocchi, D. & Peñuelas, J. (2019) The physics and ecology of mining carbon dioxide from the atmosphere by ecosystems. Glob. Change Biol., 25, 1191-1197.

[7] Chile 2017 fires: fire-prone forest plantations, jgpausas.blogs.uv.es/2017/09/16/ | Incendios en Chile 2017, jgpausas.blogs.uv.es/2017/02/10/

[8] Feng et al. 2016. Revegetation in China’s Loess Plateau is approaching sustainable water resource limits. Nature Clim Chan. 6, 1019–1022.

[9] Stephenson et al. 2014. Rate of tree carbon accumulation increases continuously with tree size. Nature 507: 90-93 [see also: link]

[10] 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]

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

Further readings: Texas AgriLife | Wired | Yale e360 | CSIC

Update (2020): additional recent references

Anderegg et al. 2020. Climate-driven risks to the climate mitigation potential of forests. Science, 368(6497).

Friggens et al. 2020. Tree planting in organic soils does not result in net carbon sequestration on decadal timescales. Global Change Biol. 26:5178–5188

Gómez-González S, Ochoa-Hueso R, & Pausas JG. 2020. Afforestation falls short as a biodiversity strategy. Science, 368(6498), 1439–1439. doi: 10.1126/science.abd3064

Goodell J. 2020. Why Planting Trees Won’t Save Us. Rolling Stone 25/6/2020.

Heilmayr et al. 2020. Impacts of Chilean forest subsidies on forest cover, carbon and biodiversity. Nature Sustain, 1–9. doi: 10.1038/s41893-020-0547-0

Jiang et al. 2020. The fate of carbon in a mature forest under carbon dioxide enrichment. Nature 580: 227-231. (evidence of the limited role of forests and plantations for CO2 mitigation)

Wang et al. 2020. Assessing the water footprint of afforestation in Inner Mongolia, China. J. Arid Environ, 182, 104257.

Bond W. 2020. Myth-busting forests: https://jgpausas.blogs.uv.es/2020/07/23/

Skelton et al. 2020. 10 myths about net zero targets and carbon offsetting, busted. www.climatechangenews.com/2020/12/11

Waring B. 2021. There aren’t enough trees in the world to offset society’s carbon emissions – and there never will be. TheConversation, 23 Apr 2021
 
Koch A, Brierley C, Lewis SL 2021. Effects of Earth system feedbacks on the potential mitigation of large-scale tropical forest restoration. Biogeosciences 18:2627–2647.
 

Wildfires as an ecosystem service (II)

October 1st, 2019 2 comments

Our paper where we emphasized the role of wildfires in providing ecosystem services [1] had a good reception among those with experience in fire ecology; but it was a surprise for people that never worked on wildfires [2]. The main criticism we have received is that it is very obvious that wildfires can produce negative effects (killing plants and animals, increasing erosion and pollution, burning houses, etc.) and we did not emphasized this in the paper. Of course! Everybody knows it! We have never denied it! In fact, if fire didn’t not kill plants and animals, it would not be an evolutionary pressure! [3]

Rain is a natural process that provides a range of services to humans but certainly not all rainfall events (eg those generating floods) are beneficial to human societies. Biodiversity can also deliver a variety of services, even though there are species capable of harming humans. Likewise, the vast majority of life depends on sunlight, yet we can get sunburn and develop skin cancer after overexposure. In the same way, wildfires can offer a range of ecosystem services [1] but obviously not all fires, and not all fire regimes, provide services to humankind. For instance, if we build houses in a fire-prone (or flood-prone) area, then the inhabitants of those houses are likely to suffer negative impacts when a wildfire (or a major rainfall event) occurs. Similarly, when we substantially increase fuel loads and landscape homogeneity (eg due to a fire exclusion policy, or with a massive and poorly managed tree plantation), the impact of wildfires – especially under novel climatic conditions – can be catastrophic (eg the case of the 2017 fires in Portugal and Chile [4]).

In more general terms, negative impacts to humans often occur when we perturb the historical fire regime: that is, when one or some of the fire regime parameters (ie frequency, seasonality, spread pattern, or intensity) are altered [5]. This is because human societies have adapted to historical fire regimes, or have modulated the fire regime for their own benefit (cultural fire regimes); however, recent abrupt fire regime changes due to modern anthropogenic factors (eg mismanagement, global warming) lead to fire regimes that adversely impact biodiversity and the services they provide (for a few examples, see [5]). This is why we previously suggested that perturbations to the historical fire regime feed back to the functioning of the ecosystem and reduce these services in the same way that major anthropogenic changes in a rainfall regime reduce the services that precipitation provides to humans [1]. Thus, the idea that wildfires can provide ecosystem services stands firmly, even though there are currently some socially unsustainable fire regimes; these negative impacts are well-known by everybody, and widely spread by the media.

 

Ucrania natural heritage site (Wikimedia, licensed under the Creative Commons).

References

[1] Pausas J.G. & Keeley J.E. 2019. Wildfires as an ecosystem service. Front. Ecol. & Environ. 17: 289-295. [doi | pdf | blog | brief for managers]  

[2] Pausas J.G. & Keeley J.E. 2019. Wildfires misunderstood. Front. Ecol. & Environ. 17: 431-431 [doi | pdf]

[3] He T., Lamont N.B., Pausas J.G. 2019. Fire as s key driver of Earth’s biodiversity. Biological Reviews [doi | pdf]  

[4] Chile 2017 fires: fire-prone forest plantations, jgpausas.blogs.uv.es/2017/09/16/ | Incendios en Chile 2017, jgpausas.blogs.uv.es/2017/02/10/

[5] Keeley J.E. & Pausas J.G. 2019. Distinguishing disturbance from perturbations in fire-prone ecosystems. Int. J. Wildland Fire 28: 282-287. [doi | IJWF | pdf | blog | brief for managers]  

 

Humboldt 250

September 14th, 2019 No comments

Recientemente un/a periodista me hizo unas preguntas sobre el artículo que escribí sobre Alexander von Humboldt y su influencia en la ecología actual [1]. Hoy, en el día en que se cumplen 250 años de su nacimiento, transcribo las preguntas y respuestas.

¿Cuál considera que fue la mayor contribución de Humboldt?

Humboldt miró la naturaleza con un rigor científico totalmente inusual en su época, realizando observaciones y mediciones especialmente novedosas. Además, esa manera de mirar la ejerció en regiones muy diversas, lo que le permitió hacer comparaciones y encontrar patrones comunes. Cabe recordar que en aquella época medir variables tan básicas como la latitud, longitud y altitud, no era nada fácil. Por ello, se puede decir que Humboldt fue el primer científico de la naturaleza, lo que hoy en día llamamos un ecólogo.


¿De qué manera sus investigaciones han influido en nuestra visión de la naturaleza?

Haekel definió el término “ecología” (como ciencia) precisamente pensando en la manera en que Humboldt miraba y analizaba la naturaleza. Humboldt se enfocó especialmente en medir variables ambientales (altitud, presión, temperatura, radiación, color del cielo, etc.), y relacionarlas con las especies y comunidades; así descubrió los gradientes altitudinales y latitudinales. Esa visión novedosa de la naturaleza estimuló a muchos naturalistas y dio origen a una nueva ciencia. Muchos naturalistas, ecólogos y biogeógrafos clásicos se inspiraron directa o indirectamente en los trabajos de Humboldt. El movimiento ecologista también se fijó en los comentarios de Humboldt sobre el papel de la humanidad en la naturaleza.


¿Deberíamos cambiar nuestra forma de ver el medioambiente? ¿Por qué?

Hemos aprendido mucho desde Humboldt, y tenemos que seguir avanzando en integrar otros tipos de procesos naturales que Humboldt no observó o no entendió. Por ejemplo, su visión estaba centrada en cómo los parámetros ambientales determinan las especies y comunidades vegetales. Hoy en día sabemos que el ambiente determina muchos procesos ecológicos, pero también sabemos que las características ambientales no lo explican todo. Gran parte de la diversidad de nuestros ecosistemas se explica por las relaciones de interacción entre especies, o por los regímenes de perturbación. Por ejemplo, es imposible entender la gran diversidad de especies en el mediterráneo, o en las sabanas africanas, sin considerar aspectos tales como los incendios y la herbivoría, que mantienen espacios abiertos donde han evolucionado un sinfín de especies que no pueden vivir en bosques o en ecosistemas con poca luz. Humboldt mostró un desconocimiento de las sabanas, que es comprensible porque aún se conocía muy poco sobre los trópicos. En las últimas décadas hemos aprendido mucho del papel de los incendios y de la fauna (actual y extinta) en moldear las especies y las comunidades.


Según su estudio, ¿qué le falta al legado de Humboldt para entender mejor la ecología?

Comprender la naturaleza requiere abordar tres aproximaciones [2]: 1) las relaciones de las especies con el ambiente, 2) las interacciones entre especies, y 3) las relaciones con las perturbaciones. Humboldt profundizó especialmente en la primera, y durante muchos años, gran parte de la ecología fue descendiente de esa visión. Hoy en día estamos aprendiendo mucho de las otras dos aproximaciones. Pero aún hay muchos libros de texto de ecología que se centran en la primera. Por ejemplo, la mayoría de estos libros de texto menciona muy brevemente el fuego y los incendios forestales, y normalmente los presentan como una perturbación que genera dinámica. Es muy raro encontrar un libro de texto que explique que los incendios son, y han sido durante muchos millones de años, una presión de selección que genera biodiversidad, y que no podemos entender una proporción muy importante de la biosfera (al menos los ecosistemas mediterráneos, las sabanas, y los bosques boreales) si no los tenemos en cuenta [3]. Es importante incluir perturbaciones como el fuego y la herbivoría en el centro de la teoría ecológica [1].

Publicaciones relacionas:

[1] Pausas J.G. & Bond W.J. 2019. Humboldt and the reinvention of nature. Journal of Ecology 107: 1031-1037. [doi | pdf] – The long shadow of Humboldt [jecol blog | jgp blog ]

[2] Pausas J.G., Lamont B.B. 2018. Ecology and biogeography in 3D: the case of the Australian Proteaceae. Journal of Biogeography 45: 1469-1477. [doi | pdf]  

[3] He T., Lamont N.B., Pausas J.G. 2019. Fire as s key driver of Earth’s biodiversity. Biological Reviews [doi | pdf]  

 

Fish and fire

September 12th, 2019 No comments

Are the fish adapted to fire? How can fish benefit from wildfire? The answer is in this 5-minute video.

For more information on animal adaptations to wildfires see:

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

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

 

Fire, grasses, and buds

August 26th, 2019 No comments

The traditional view is that C4 grasses are more efficient in open, dry, and warm habitats because they are able to fix more carbon under warm and sunny environments than C3 grasses. However, these habitats are also likely to be fire-prone, and thus their survival may depend on the bud protection mechanisms. Using data from a previous postfire resprouting experiment [1] we show that plant mortality and resprouting response are better explained by the location of the buds than by the photosynthesis pathway (C3 vs C4) [2]. Grasses with aerial buds (stolons) are more exposed to fire and have higher mortality and less resprouting than those with belowground buds (rhizomes); those with buds in the root-crown show an intermediate response (Fig. 1 below). This suggests that carbon reserves are not the only limiting factor for resprouting. The first requirement for initial resprouting is the survival of the bud bank, which depends on the degree of bud protection [3]. Once the initial resprouting occurs, the carbon reserves and the new photo-assimilates should determine the resprouting vigour [4]. In conclusion, to fully understand the variability in postfire resprouting in grasses we need to consider the location and the degree of protection of the bud bank [3]. The bud bank could also had a role, together with C4 photosynthesis, in the massive C4 grass expansion during the Late Miocene (3-8 Ma).

Fig. 1. Mean proportion of postfire tillers in relation to prefire tillers in Australian grasses across treatments aggregated by the species that have different bud locations (stolons, crown, rhizomes), and by the different photosynthetic pathway (C3, C4). From [2].

References

[1] Moore NA, Camac JS, Morgan JW. 2019. Effects of drought and fire on resprouting capacity of 52 temperate Australian perennial native grasses. New Phytologist 221:1424–1433.

[2] Pausas J.G. & Paula S. 2020. Grasses and fire: the importance of hiding buds. New Phytologist [doi | pdf]

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

[4] Moreira B., Tormo J, Pausas J.G. 2012. To resprout or not to resprout: factors driving intraspecific variability in resprouting. Oikos 121: 1577-1584. [doi | pdf]  

Fire as a key driver of Earth’s biodiversity

July 12th, 2019 2 comments

Regions subject to regular fire have exceptionally high levels of species richness and endemism, and fire is likely a major driver of their diversity. In a recent paper [1] we reviewed the mechanisms that enable fire to act as a major ecological and evolutionary force that promotes and maintains biodiversity over different spatiotemporal scales. Specifically, we reviewed the different components of fire regime, the diversity through time (postfire), the intermediate disturbance hypothesis, the pyrodiversity-begets-biodiversity hypothesis, the fire-driven evolution and diversification, and the mutagenic effect of fire.

From an ecological perspective, the vegetation, topography and local weather conditions during a fire generate a landscape with spatial and temporal variation in fire-related patches (pyrodiversity), and these produce the biotic and environmental heterogeneity that drives biodiversity across local, regional and global scales scales [2]. We show that biodiversity should peak at moderately high levels of pyrodiversity. Overall species richness is typically greatest immediately after fire and declines monotonically over time, with postfire successional pathways dictated by animal habitat preferences and varying lifespans among resident plants.

From an evolutionary perspective, fire drives population turnover and diversification by promoting a wide range of adaptive responses to particular fire regimes [3,4]. In addition, fire and its byproducts may have direct mutagenic effects, contributing to the formation of novel genotypes that can lead to trait innovation. As a consequence of all these processes, the number of species in fire-prone lineages is often much higher than that in their non-fire-prone sister lineages.

Figure 1: The six components that define an individual fire event (in red the two core components). The fire regime arises from repeated patterns (means plus variance) over time of the properties of the components for each fire. For more details, see [1].

Figure 2. Relationship between species richness (S) of a reference area (community, landscape, region) and mean fire interval (a fire regime component). For a given fire regime, there is a mosaic of patches defined by different times since the last fire (represented by black circles) about the mean time interval (central circle). For more details, see [1].

 

References

[1] He T., Lamont B.B., Pausas J.G. (2019). Fire as s key driver of Earth’s biodiversity. Biological Reviews [doi | pdf]

[2] Pausas J.G. & Ribeiro E. 2017. Fire and plant diversity at the global scale. Global Ecol. Biogeogr. 26: 889–897. [doi | pdf | data & maps (figshare)]

[3] Keeley J.E., Pausas J.G., Rundel P.W., Bond W.J., Bradstock R.A. 2011. Fire as an evolutionary pressure shaping plant traits. Trends in Plant Science 16: 406-411. [doi | pdf]  

[4] Pausas J.G. & Keeley J.E., 2014. Evolutionary ecology of resprouting and seeding in fire-prone ecosystems. New Phytologist 204: 55-65. [doi | pdf]  

Fire promotes pollinators

June 14th, 2019 1 comment

In ecosystems with a dens vegetation, wildfires open the canopy and create an environment with more light and less competition. In such postfire conditions there is an increase in flowers, and thus, flower visitors are also likely to increase. In a recent article [1] we performed a meta-analysis to specifically evaluate the effect of fire (prescribed and wildfires) on pollinators from 65 studies in 21 countries across de globe. The overall effect of fire on abundance and richness of pollinators across all studies was positive. The positive effect was especially clear after wildfires and for the abundance and diversity of Hymenoptera (bees, wasps, etc.; the main group of pollinators), while Lepidoptera (butterflies and moths) abundance showed a negative response. Short fire intervals also showed a negative effect on pollinators. In conclusion, pollinators are not only resilient to fire, but they tend to be promoted during the first postfire years. That is, fires by increasing the number of flowers, they also increase the number of flower visitors. It is also likely that this may have a positive cascading effects on other interacting species, like seed dispersers and predators. This is one of the mechanisms by which wildfires increase diversity. Pollinations is also one of the ecosystem services that fires can provide to humans [2].

 

 

Figure:  Weighted-mean effect sizes and 95% bias-corrected confidence intervals on abundance (closed circles) and richness (open circles) of pollinator taxa. This is for wildfire only. Sample sizes for each category are shown on the right of each effect. From [1].

References

[1] Carbone L.M., Tavella J., Pausas J.G., Aguilar R. 2019. A global synthesis of fire effects on pollinators. Global Ecology & Biogeography. [doi | pdf]

[2] Pausas J.G. & Keeley J.E. 2019. Wildfires as an ecosystem service. Frontiers in Ecology and Environment 17: 289-295. [doi | pdf | post]

 

Burning for biodiversity

June 1st, 2019 No comments

Taiga alive: Burning for biodiversity conservation in the boreal forest (Sweden):

This video is also available in youtube.

More videos on burning for biodiversity are available for Australia, North Carolina, New hamphshire, Florida, … , See also, a fire ecology lesson from the Florida scrub.

 

Wildfires as an ecosystem service

May 7th, 2019 No comments

Wildfires are often viewed as destructive disturbances. In a recent paper we propose that when including both evolutionary and socioecological scales, most ecosystem fires can be understood as natural processes that provide a variety of benefits to humankind [1]. Wildfires provide open habitats that enable the evolution of a diversity of shade-intolerant plants and animals that are a source of products used by humans since long ago. Wildfires also regulate pests and catastrophic fires, contribute to the regulation of the water and carbon cycles, and could help plants in their adaptation to novel climates. That is, there are many provisioning, regulating, and cultural services that we obtain from wildfires (box below).  Prescribed fires are a tool for mimicking the ancestral role of wildfires in a highly populated world.

Figure: Schematic representation of the factors occurring at the evolutionary (green square) and at the socioecological (yellow square) scale associated with fire regimes and ecosystem services. Natural (historical) wildfire regimes create open habitats that can promote specific adaptations, biodiversity, and overall functioning in fire-prone ecosystems; these are the supporting services necessary for the production of all other services (table below). Decisions and policies may modify fire regimes (anthropogenic fire regimes) modulating ecosystem functioning and services (socioecological feedback); that is, policy decisions may switch between maintaining ecosystem services (stabilizing feedback) or generating unsustainable fire regimes (disruption of the feedback). Decisions and policies (bottom right corner) include fire and landscape management decisions, but also include socioeconomic changes that have implications on fire regimes (eg rural abandonment [2]). From [1].

Examples of ecosystem services provided by recurrent wildfires to early and to contemporary societies. For more details, see [1]:

  • Provisioning services:
    – Provide open spaces for pastures, agriculture, and hunting
    – Stimulate germination of desirable annual ‘crops’ postfire
    – Provide carbohydrates from underground plant organs
    – Provide craft and basketry material (resprouts)
    – Maintaining open spaces for grazing and hunting
    – Provide essences, medicines, flowers (ornamental)
  • Regulating services
    – Pest control for humans and livestock
    – Reduce catastrophic wildfires
    – Accelerates species replacement in changing conditions
    – Enhance flowering and pollinator activity
    – Water regulation
    – Carbon balance
  • Cultural services
    – Spiritual, inspirational
    – Ecotourism in open ecosystems
    – Recreational hunting
    – Scientific knowledge on the origin of biodiversity
    – Knowledge on ancestral fire management techniques

 

Cover of the June 2019 issue of Frontiers in Ecology & Environment (17, 6) where our papers is featured. California poppy (Eschscholzia californica) flowering postfire enhances pollination.

 

Illustrating ecosystems services by fire is not easy; here are some examples of pictures I received to potentially illustrate this paper; most of them did not finally go to the paper. Thanks to the contributes! – [click the photo to enlarge]

 

References

[1] Pausas J.G. & Keeley J.E. 2019. Wildfires as an ecosystem service. Frontiers in Ecology and Environment 17: 289-295 [doi | pdf | summary for managers]

[2] 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]  

 

Postfire in a Mexican arid ecosystem

April 24th, 2019 No comments

Arid ecosystems have a climate appropriate for fires, but their low biomass often limits the frequency and intensity of fires; yet they still occur. A recent study evaluated the survival and resprouting of four species 6 months after a fire [1] in Tehuacán-Cuicatlán Biosphere Reserve (Puebla, Mexico), and show that most individuals of the four species survived:

  • Dasylirion lucidum (Asparagaceae): the apical bud of most (97%) plants survived and quickly produced new leaves; few individuals shows basal resprouts.
  • Juniperus deppeana (Cupressaceae): 75% of the trees survived, some resprout from the base, others from epicormic buds (see also here)
  • Echinocactus platyacantus (Cactaceae): 95% survived
  • Agave potatorum (Asparagaceae): 90% survived and continued to growth new leaves from the central of the plants

All species are endemic of Mexico except Juniperus deppeana that also occurs in the southwestern USA (Arizona, Texas, New Mexico).

 

Landscape dominated by Dasylirion lucidum 6 months after a fire in Tehuacán, Mexico [1].

 

Dasylirion lucidum (a), Juniperus deppeana with epicormic resprouts (b), Echinocactus platyacantus (c), and Agave potatorum (d) six months postfire in Tehuacán, Mexico [1].

 

References

[1] Rodríguez-Trejo, D. A., Pausas, J. G. & Miranda-Moreno, A. G. 2019. Plant responses to fire in a Mexican arid shrubland. Fire Ecology 15:11 [doi | pdf]  

[2] Pausas J.G. Flammable Mexico. Int. J. Wildland Fire 25: 711-713 [doi | pdf]

More on: México fires | Juniperus deppeana postfire |