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Posts Tagged ‘fire regime’

Entrevista

October 19th, 2023 No comments

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

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

Conferencia: Incendios y biodiversidad

September 17th, 2023 No comments

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

Fire increases precocity in pines

December 24th, 2022 No comments

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

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

References

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

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

Evolutionary Ecology of Fire

November 4th, 2022 1 comment

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

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

References

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

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

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

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

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

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

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

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

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

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

Alternative Biome States in Brazil

October 31st, 2022 No comments

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

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

References

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

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

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

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

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

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

Incendis forestals: carta al poble valencià

September 10th, 2022 No comments

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

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

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

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

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

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

Fire regimes across the western Palearctic

July 20th, 2022 No comments

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

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

References

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

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

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

Feedbacks in ecology and evolution

April 21st, 2022 No comments

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

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

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

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

References

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

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

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

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

Fire-released seed dormancy

April 8th, 2022 No comments

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

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

References

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

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).

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.

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]

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.]

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]  

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]  

 

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]  

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]  

 

Disturbance and perturbations

April 18th, 2019 No comments

Fire is a key process in many ecosystem (fire-prone ecosystems), where it is best viewed as a natural disturbance that benefits to ecosystem functioning. However, increasingly, we are seeing human interference in fire regimes that alters the historical range of variability for most fire parameters and results in vegetation shifts. Such perturbations can affect all fire regime parameters. In a recent paper [1] we provide a brief overview of examples where anthropogenically driven changes in fire frequency, fire pattern, fuels consumed and fire intensity constitute perturbations that greatly disrupt natural disturbance cycles and put ecosystems on a different trajectory resulting in type conversion. These changes are not due to fire per se but rather anthropogenic perturbations in the natural disturbance regime. That is, the critical factor determining system resilience is not fire but the perturbations of fire regime. Of course, in ecosystems where fire is not a natural process (e.g., rainforests), we should consider fire itself to be a perturbation.

Examples of perturbations of the fire regime, specifically alterations of the fire interval:


Entire chaparral landscape in the frame burned in 1970, half of the foreground burned again in 2001 and the far right third of the foreground burned a third time in 2003, all by human-caused ignitions. Vegetation recovery following the 2001 fire comprises native shrub and subshrub regeneration, those areas burned a third time in 2003 are dominated by alien red brome grass invasion (photo by R. W. Halsey [1]).

 


Massive lodgepole (Pinus cortata) forest regeneration following the 1988 North Fork Fire, which burned over 200.000 ha of Yellowstone lodgepole forests, was partially reburned after 28 years in the 2016 Maple Fire of 18.200 ha. This atypical short interval resulted in very little regeneration (immaturity risk); casual observations in the summer of 2018 revealed, 10 to 1 ratio of adult skeletons to seedlings, clearly not stand-replacing recruitment (photo by J. E.Keeley [1]).

 

References

[1] Keeley J.E. & Pausas J.G. 2019. Distinguishing disturbance from perturbations in fire-prone ecosystems. Int. J. Wildland Fire [doi | IJWF | pdf]

 

Global change in the Mediterranean basin

January 9th, 2019 2 comments

The paleartic region with mediterranean climate (southern Europe and northern Africa; the Mediterranean Basin; Fig. 1) is a hotspot of biodiversity, a hotspot of climate change (warming of the region is above global average), and a hotspot of human population (a highly populated area and a top tourist and retirement destination). In addition, the Mediterranean Sea is the world’s largest inland sea, and climatic disruptions in the region have consequences in the large catchment area that includes central-eastern Europe (Fig. 1). That is, environmental changes and disruptions of the water cycling in the Mediterranean region have consequences affecting a large human population [1].

Fig. 1. Area with mediterranean climate (green) and limits of the Mediterranean catchment (red).  The European catchment limit based on Cortambert (1870). From [1]; shape files available here.

The region, as all the planet, is subject to global warming. In addition there are three main local processes (not directly related to global warming) that are very important in understanding dynamic changes in the region [1]:

a) Rural abandonment in an environment depauperate of native herbivores; this increases wildlands (greening) but also the abundance and continuity of fuels that feed wildfires [2]

b) Increasing the wildland-urban interface; this increases biodiversity degradation (e.g., alien species), fire ignitions, and the vulnerability of the society to fires

c) Coastal degradation enhances drought (browning) through negative feedback processes; that is, the desiccation of coastal marshes, the deforestation for agriculture, and more recently, the explosive coastal urbanization, have drastically reduced the original ecosystems and thus the water available for the sea breeze that was once feeding the rain in the upper part of the mountains [1].

All these mechanisms act in different directions (greening, browning), and the current balance is still towards greening, as land abandonment is buffering the browning drivers; however, it is likely to switch with global warming. The challenge is to mitigate the browning processes. The good news is that the importance of small-scale drivers suggests that local policies and actions can make a difference in reducing overall impact on the landscape and society.

Mechanisms acting at a fine scale, together with global drivers (CO2 enrichment and climatic warming) interact and drive current vegetation changes in Mediterranean landscapes. Any model aiming to predict the future of our vegetation and climate must consider these local mechanisms; and failing to consider them at an appropriate scale is likely to produce inconclusive predictions.

Fig. 2. The disruption of the natural fire and drought regimes in Mediterranean landscapes is driven by global and local drivers. Increased fire activity is a response to the fuel amount and landscape homogeneity generated by rural abandonment (fire hazard) in an environment depauperated of herbivores and with increasing human ignitions (fire risk) and droughts (fire weather). The increased dry conditions are the consequence of global warming, but also of storm losses caused by the disruption of the water cycle generated by the coastal degradation. WUI: wildland-urban interface. From [1].

References

[1] Pausas J.G. & Millán M.M. 2019. Greening and browning in a climate change hotspot: the Mediterranean Basin. BioScience 69: 143-151 [doi | OUP | pdf | map (shape file)]  

[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]  

Every time you build anything, a highway, a school, whatever, you are altering the precipitation regime somewhere downwind” Millán M. Millán

Socioeconomics and fire regime in the Mediterranean

August 26th, 2017 No comments

In recent decades, fires in Mediterranean Europe have become larger and more frequent. This trend has been driven mainly by socioeconomic changes that have generated rural depopulation and changes in traditional land use. This has increased the amount and continuity of vegetation (fuel), and thus an increase in the fire size and area burnt [1-3]. In a recent paper [4] we compared fire statistics of the Western Rif (Morocco) with those form Valencia (eastern Spain) to show that current fire regimes in Mediterranean Africa resemble past fire regimes in the Mediterranean Europe when rural activities dominated the landscape. The temporal fire regime shift observed in different countries of the Mediterranean Europe (from small, fuel-limited fires to drought-driven fires) can be identified when moving from the southern to the northern rim of the Basin. That is, most spatial and temporal variability in fire regimes of the Mediterranean Basin is driven by shifts in the amounts of fuel and continuity imposed by changes in socioeconomic drivers (e.g., rural depopulation). In fact, we can use rural population density as an early warning for abrupt fire regime shift. Consequently we can predict future fire regimes in North Africa, based on the trends observed in southern Europe, and we can better understand past fire regimes in Europe based on the current situation in North Africa [4].


Figure 1. Western Rif (northern Morocco) and Valencia (eastern Spain).


Figure 2. Fire-size distribution in Valencia, for the period 1880-1970 (white boxes) and for the period 1975-2014 (grey boxes), and in the western Rif (red symbols, 2008-2015). For details see [4]

References

[1] Pausas, J.G. 2004. Changes in fire and climate in the eastern Iberian Peninsula (Mediterranean basin). Climatic Change 63: 337-350. [pdf | doi]

[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. & Paula S. 2012. Fuel shapes the fire-climate relationship: evidence from Mediterranean ecosystems. Global Ecol. & Biogeogr. 21: 1074-1082. [doi | pdf | supp]  

[4] Chergui B., Fahd S., Santos X., Pausas J.G. 2018. Socioeconomic factors drive fire-regime variability in the Mediterranean Basin. Ecosystems 21: 619–628 [doi | pdf]

 

Incendios, arte y divulgación

July 18th, 2017 No comments

1) La Fundación Pau Costa ha puesto el punto 1 del decálogo de incendios forestales (punto que escribí yo), en un marco artístico para facilitar la divulgación:

El decálogo completo en:  enlace (¡firma!) | pdf | post | English

  
2) Fragmento de la entrevista para el reportaje “Uno de los nuestros”, dirigido por Paco Quintans, y estrenado en Noviembre del 2017

El documental entero disponible está en Youfeelm.

 

3) Fragmento del documental “La Huella del fuego” del programa Crónicas, de La 2 de RTVE (28 Noviembre del 2016)

El documental entero se puede ver en: www.rtve.es/alacarta | jgpausas.blogs.uv.es/2016/11/30
 

Fire and diversity

May 26th, 2017 1 comment

In a recent paper [1], we studied the relationship between plant diversity (Fig. 1a) and fire activity (Fig. 1b) for the different ecoregions of the world, and found a strong positive relationship (Fig. 2), even after taking into account productivity and other major environmental variables [1]. This is the first global assessment of the importance of fire as major determinant of species diversity. There are at least two (not mutually exclusive) mechanisms by which fire may drive plant diversity at the scale and grain considered. 1) A selective process; there is both micro and macro evolutionary evidence suggesting that fire regime can drive population divergence and diversification [2-5]. And 2) Fires generate landscape mosaics and thus more habitat types and more niches likely to be filled by different species. In fact, the two processes are linked as landscape mosaics are also appropriate frameworks for population divergences and selective processes in fire-prone ecosystems [6]. That is, our results suggest that fire generates the appropriate conditions for a large variety of plants in many regions worldwide. Or, in other words, a world without fires (if possible at all) would be less diverse.

 


Fig. 1. Maps of plant diversity (logarithm of the number of species divided by the ecoregion area) and fire activity (estimated by 15 years of remote sensing data for each ecoregions, standardized from 0 to 1) for each terrestrial ecoregion of the world. From [1].


Fig. 2. Plant diversity in each terrestrial ecoregion (number of species divided by area, log scale; Fig. 1a) plotted against an indicator of fire activity (Fig. 1b); the two lines refer to fitted lines for low and high radiative power (an indicator of fire intensity). Form [1].

References

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

[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., Alessio G., Moreira B. & Corcobado G. 2012. Fires enhance flammability in Ulex parviflorus. New Phytol. 193: 18-23. [doi | wiley | pdf]

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

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

[6] Castellanos, M.C., González-Martínez, S. & Pausas, J.G. 2015. Field heritability of a plant adaptation to fire in heterogeneous landscapes. Mol. Ecol. 24, 5633-5642. [doi | pdf | suppl.]  

 

 

The ecology of bark thickness (2): another twist

December 3rd, 2016 No comments

Sometime ago we proposed that “at the global scale, a significant proportion of the variability in bark thickness is explained by the variability in fire regimes”, and specifically predicted that frequent low intensity fires select for thick bark [1]. In addition, we suggested that differentiating between inner and outer bark thickness would help to better understand the functional role of bark, especially in non-fire prone ecosystems. The paucity of available data at a global scale limited an empirical demonstration of the proposed framework.

A recent paper has now provided evidence for the fire hypothesis of bark thickness at a global scale [2, 3]. Specifically, Rosell [2] regressed bark thickness against fire frequency and climate parameters and showed that the most sensitive part of the bark in relation to fire was the outer bark, while the inner bark was quite variable and slightly related to both fire and climate [2]. In the early paper [1] we also mentioned that little was known about the role of bark thickness in arid ecosystems. Recent research support the role of bark as a fire protection mechanisms in some arid ecosystems [4, 5].

To advance in the relationship between bark thickness and fire, it is necessarily to consider not only fire frequency, but also fire intensity, and to scale these fire characteristics with plant life-histories ([3], see figure below). This is because the relationship between fire regime and bark thickness is not expected to be simple and linear, but a bit more complex, including some threshold-type relationships (figure below).

Little by little we are improving our understanding on the role of bark as a fire-protection mechanism, and how fire regimes has shaped bark thickness in many ecosystems.

Fig2_FlameHeight-FRI_art

Figure: Bark thickness as a function of fire regime: flame height (an indicator of fire intensity) and mean fire return interval (fire frequency). Fire regime is scaled by the characteristics of the plant (height to the base of the crown and longevity, respectively). The shaded area represents the areas where thick bark is adaptive for fire protection, i.e., when return intervals are shorter than the lifespan of the plant and fires are of low intensity (flame height is shorter than the distance to the base of the crown, e.g., surface fires); the shade area is limited thresholds (values of 1 in the axes). The unshaded area represents the conditions where thick barks are not adaptive (thin bark is more likely), i.e., when fires are crown-fires or when the return interval is long (in relation to the longevity of the plant). From [3].

References

[1] Pausas, J.G. 2015. Bark thickness and fire regime. Functional Ecology 29:317-327. [doi | pdf | suppl. | blog]

[2] Rosell J.A. 2016. Bark thickness across the angiosperms: more than just fire. New Phytologist 211: 90–102

[3 ] Pausas J.G. 2017. Bark thickness and fire regime: another twist. New Phytologist 213: 13-15. [doi| pdf] <- New!

[4] Schubert, A. T., Nano, C. E. M., Clarke, P. J. & Lawes, M. J. 2016. Evidence for bark thickness as a fire-resistance trait from desert to savanna in fire-prone inland Australia. Plant Ecol. 217: 683-696.

[5] Cousins, S. R., Witkowski, E. T. F. & Pfab, M. F. 2016. Beating the blaze: Fire survival in the fan aloe (Kumara plicatilis), a succulent monocotyledonous tree endemic to the Cape fynbos, South Africa. Austral Ecol. 41:466-479.

Disturbance maintains alternative biome states

November 9th, 2015 No comments

It is becoming more and more evident that climate alone does not explain spatial and temporal patterns of the world vegetation, and that disturbance regimes explain an important part of the variability in vegetation and biome composition and distribution [1]. This has been suggested specially in tropical ecosystems where alternative vegetation states (e.g., forests and savannas) are possible for a given climatic conditions [2]. For instance, in dry years, surface fires may enter in forests and kill fire-sensitive trees and select for fire-resistant woody species with open crown architectures that generates well lit communities with a flammable grassy understory. Forest trees and savannas trees have a marked difference in bark thickness (thinner in the former) and thus a contrasted sensitivity to surface fires [3]. Thus, a switch to a forest state from a savanna depends on a sufficiently long fire interval or high resource availability allowing the outcompetition of shade-intolerant savanna trees and grasses (i.e. the inhibition of fires) by means of a closed canopy of forest trees. Similarly, herbivory can also exert a control on woody biomass and favour herbivory-resistant shrubs and grasses. However, empirical (field-based) evidence for alternative sates were very limited. In a recent paper [4] we used field data to show that, for a wide range of environmental conditions (in South America and Africa), fire feedbacks maintain savannas and forests as alternative biome states in both the Neotropics and the Afrotropics. In addition, wooded grasslands and savannas occurred as alternative states in the Afrotropics, depending on the relative importance of fire and herbivory feedbacks. That is, we found evidence for a disturbance-driven bistability in the Neotropics and a disturbance-driven tristability in Afrotropics (figure below).

Savanna-states

Fig. Top: Frequency distribution of basal area in afrotropical (tristability) and neotropical (bistability) ecosystems. Bottom: The discontinuous pattern of basal area along the resources gradient for both afrotropical and neotropical ecosystems (red: wooded grasslands; orange: savannas; green: forests). Note that there are regions of the gradient where two alternative vegetation types are possible; they are maintained by different disturbance regime (see [4]).

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

[2] Dantas V., Batalha MA & Pausas JG. 2013. Fire drives functional thresholds on the savanna-forest transition. Ecology 94:2454-2463. [doi | pdf | appendix]

[3] Pausas, J.G. 2015. Bark thickness and fire regime. Funct. Ecol. 29: 317-327. [doi | pdf | suppl.]

[4] Dantas V.L., Hirota M., Oliveira R.S., Pausas J.G. 2016. Disturbance maintains alternative biome states. Ecology Letters 19:12-19 [doi | wiley | pdf |supp.– New!

[5] Update (a new relevant paper): Pausas J.G. & Dantas V.L. 2017. Scale matters: Fire-vegetation feedbacks are needed to explain tropical tree cover at the local sacle. Global Ecol. Biogeogr. 26: 395–399. [doi | pdf | post ]

Ecology and evolution in fire-prone ecosystems

February 28th, 2015 2 comments

During the last years I’ve been working in many topics related to fire ecology and plant evolution in ecosystems subject to recurrent fires (mainly mediterranean and savanna ecosystems). Because I believe knowledge should be spread around easily, I make my results available to the public in my web page (see publications list) and in this blog. However, having the cumulative list of paper published each year is not very convenient for people searching for a specific topic. For this reason, I’m rearranging most of my articles by topics as follows:

1. Fire history
2. Fire regime: climate & fuel
3. Fire traits (resprouting, postfire germination, serotiny, bark thickness, flammability, data & methods)
4. Fire & plant strategies (in Mediterranean ecosystems, in pines, in savannas, community assembly)
5. Fire & evolution
6. Some fire-adapted species (Pinus halepensis, Quercus suber, Ulex parviflorus)
7. Fire & vegetation modelling
8. Plant-animal interactions
9. Restoration & conservation

See: fire-ecology-evolution.html

Some papers may be repeated if they clearly fit in more than one topic; some papers, mainly old ones, do not fit well in any of these topics and have not been included (at least at the moment), they still can be found in the section of publications sorted by year. I’m still working on this rearrangement, so some modifications are possible; and any comment is welcome.
I hope this is useful for somebody!

Publications: by year | by topic | books

 

The ecology of bark thickness

December 1st, 2014 No comments

Bark is a vital and very visible part of woody plants, yet the functional and evolutionary ecology of the bark is still poorly understood. In a recent article I have studied one of the bark properties: bark thickness [1]. Bark thickness is very variable among woody plants and fire is a key factor selecting for a thick bark. This is because barks are very good heat insulators and under low intensity fires, small differences in bark thickness provides a great increase in the stem protection and survival. Consequently, at the global scale, an important proportion of the variability in bark thickness should be explained by the variability in fire regimes. In this paper I provide evidences supporting the role of fire regime in shaping bark thickness (in conjunction with other plant traits) on a global scale [1].

Forest environments with very frequent (and low intensity) understory fires select for trees with thick bark at the base of the bole. In some savannas, trees do not have specially thick barks as they tend to growth quickly to escape the height affected by grass fires. Savannas living in poor soils may not be able to growth quickly and thus trees can only survive if they have a very thick bark in the whole plant (including in the thin branches). In Mediterranean ecosystems, fires are less frequent than in savannas, and there is time for the accumulation of fine woody biomass. Consequently, fires burns intensely (crown fires) and thus small differences in bark thickness do not increase stem survival; in such conditions, most species have relatively thin barks. In wet tropical forests, tree barks are very thin because fire are very rare and thus a thick bark is not advantageous. In very arid ecosystems, fuels are too sparse for fire spread, and thus the observed variability in bark thickness is related to other factors like a response to water stress. In conclusion, fire regimes can explain a large proportion of the variability of bark thickness at the global scale, and thus this trait varies across ecosystems in a predictable manner.

thick-bark2

Figure: Examples of trees with thick bark: A. Myrcia bella (Myrtaceae, Brazil); B. Quercus suber (Fagaceae, Mediterranean Basin), in the cover of the book ‘Cork oak Woodlands on the Edge’ [2]; C: Eremanthus seidelii (Asteraceae, Brazil); and D: Enterolobium gummiferum (Fabaceae), small top branch. Photos from [1] and [2].

References

[1] Pausas, J.G. 2015. Bark thickness and fire regime. Functional Ecology   [doi | pdf | suppl.]

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

Alternative fire-driven vegetation states

November 1st, 2014 No comments

One of the clearest pieces of evidence for the role of fire in shaping vegetation is the occurrence of alternative vegetation types maintained by different fire regimes in a given climate. The different flammability of alternative communities generates different fire feedback processes that maintain contrasted vegetation types with clear boundaries in a given environment; and fire exclusion blurs this structure. This has been well documented in tropical landscapes (e.g., [1]) that are often mosaics of two alternative stable states – savannas and forests – with distinct structures and functions and sharp boundaries. Currently, there is an increasing evidence that alternative fire-driven vegetation states do occur in other environments, including temperate forests ([2, 3] and figure below). That is, the existence of alternative fire-driven vegetation states may be more frequent than previously thought, although human activities may favour one of the states and mask the original bistability.

modelv2

Figure: Factors determining the transition between two alternative vegetation states (fire sensitive forest and fire resilient shrubland) in a temperate landscape in Patagonia. Human factors (global warming, increased ignitions, and livestock grazing) favour transition to shrublands. From [2].

References
[1] Dantas V., Batalha MA & Pausas JG. 2013. Fire drives functional thresholds on the savanna-forest transition. Ecology 94:2454-2463.  [doi | pdf | appendix]

[2] Pausas, J.G. 2015. Alternative fire-driven vegetation states. Journal of Vegetation Science 26: 4-6 [doi | pdf | suppl.]

[3] Paritsis J., Veblen T.T. & Holz A. 2014. Positive fire feedbacks contribute to shifts from Nothofagus pumilio forests to fire-prone shrublands in Patagonia. J. Veget. Sci., 26.

 

Evolutionary ecology of resprouting and seeding

July 15th, 2014 No comments

There are two broad mechanisms by which plant populations persist under recurrent fires: resprouting from surviving tissues, and seedling recruitment [1]. Species that live in fire-prone ecosystems can have one of these mechanisms or both [1]. In a recent review paper [2], we propose a model suggesting that changes in evolutionary pressures that modify adult (P) and juvenile (C) survival in postfire conditions (Fig. 1 below) determine the long-term success of each of the two regeneration mechanisms, and thus the postfire regeneration strategy: obligate resprouters, facultative species and obligate seeders (Fig. 2). Specifically we propose the following three hypotheses: 1) resprouting appeared early in plant evolution as a response to disturbance, and fire was an important driver in many lineages; 2) postfire seeding evolved under conditions where fires were predictable within the life span of the dominant plants and created conditions unfavorable for resprouting; and 3) the intensification of conditions favoring juvenile survival (C) and adult mortality (P) drove the loss of resprouting ability with the consequence of obligate-seeding species becoming entirely dependent on fire to complete their life cycle, with one generation per fire interval (monopyric life cyle). This approach provides a framework for understanding temporal and spatial variation in resprouting and seeding under crown-fire regimes. It accounts for patterns of coexistence and environmental changes that contribute to the evolution of seeding from resprouting ancestors. In this review, we also provide definitions and details of the main concepts used in evolutionary fire ecology: postfire regeneration traits, postfire strategies, life cycle in relation to fire, fire regimes (Box 1), costs of resprouting (Box 2), postfire seeding mechanisms (Box 3), and the possible evolutionary transitions (Box 4).

 

Fig2_sm
Fig. 1 : Main factors affecting adult and offspring seedling survival (P and C, respectively), and thus the P/C ratio, in fire-prone ecosystems (from Pausas & Keeley 2014 [2]).

 

Fig3_sm

Fig. 2: The changes in the probability of resprouting along an adult-to-offspring survival (P/C) gradient are not linear but show two turning points related to the acquisition of key innovations: the capacity to store a fire-resistant seed bank (postfire seeding), and the loss of resprouting capacity. Changes in P/C ratio may be produced by different drivers (Fig. 1) which drove the rise of innovations during evolution, e.g., during the increasing aridity from the Tertiary to the Quaternary (from Pausas & Keeley 2014 [2]).

 

Refecences

[1] Pausas, J.G., Bradstock, R.A., Keith, D.A., Keeley, J.E. 2004. Plant functional traits in relation to fire in crown-fire ecosystems. Ecology 85: 1085-1100. [doi | pdf | esa | jstor]

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

 

Climate-independent fire regime changes

May 16th, 2014 No comments

It is well-known that fire regimes are strongly linked to climate, however, there are examples in which most variability in fire regime changes are better attributed to drivers other than climate. For instance, vegetation (fuel structure and continuity) also plays a role in shaping fire regimes [1-5]. In a recent paper [6], we reviewed evidences from different environmental and temporal settings of abupt fire regimes changes that are not directly attributed to climatic changes, but to changes driven by (i) fauna, (ii) invasive plant species, and (iii) socio-economic and policy changes. All these drivers might generate nonlinear effects of landscape changes in fuel structure; that is, they generate fuel changes that can cross thresholds of landscape continuity and thus drastically change fire activity (figure below). The importance of climate-independent factors in abrupt fire regime changes can be viewed positively: while climate is very difficult to modify at short term, fuels can potentially be managed to shape fire regimes and to mitigate the effects of global warming [7]. However the success of these actions may be diverse, depending on the historical fire regimes and the adaptive traits of the species in the community [8].

Fig1_land3seed12

Figure: Schematic representation of how a gradual change in a driver (e.g., a constant colonization or invasion of a flammable plant) can produce an abrupt change in landscape structure (e.g., continuity of the flammable vegetation). The bottom panel represents the changes through time in mean and maximum patch size in an idealized landscape that is invaded by plants (green cells) with a constant probability (p= 0.01 in each time step). The upper panel shows three snapshots of these dynamics (time steps = 25, 75 and 125, also represented by vertical lines in the bottom panel). From Pausas & Keeley [6].

References

[1] Pausas, J.G. 2004. Changes in fire and climate in the eastern Iberian Peninsula (Mediterranean basin). Climatic Change 63: 337-350. [pdf | doi]

[2] Pausas J.G. & Bradstock R.A. 2007. Fire persistence traits of plants along a productivity and disturbance gradient in Mediterranean shrublands of SE Australia. Global Ecology & Biogeography 16: 330-340.  [pdf | doi]

[3] Pausas J.G. & Paula S. 2012. Fuel shapes the fire-climate relationship: evidence from Mediterranean ecosystems. Global Ecol. & Biogeogr. 21: 1074-1082.  [doi | pdf | supp]

[4] 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]

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

[6] Pausas J.G. & Keeley J.E., 2014. Abrupt climate-independent fire regime changes. Ecosystems 17: 1109.1120 [doi | pdf] – New!

[7] Towards prescribed fires, jgpausas.blogs.uv.es, 7 Oct 2013.

[8] 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(8): 406-411. [doi | trends | pdf]

 

Fire drives trait divergence: smoke-induced germination

April 3rd, 2014 No comments

There is an increasing evidence that recurrent fires are driving within species phenotypic variability, and that different fire regimes can generate trait divergence among populations [1]. For instance, populations of the annual species Helenium aromaticum (Asteraceae) growing under different fire histories in Chile have different seed traits in such a way that the anthropogenic increase in fire frequency selected for an increasing in seed pubescence [2]. In the Mediterranean Basin there is also evidence of phenotypic divergence among populations under different fire regimes: Ulex parviflorus (Fabaceae) plants living under high fire frequency are more flammable than those growing in sites that have not suffered fires [3-5]; Pinus halepensis and P. pinaster living under high crown-fire frequency have higher serotiny that those living in areas that rarely burn in crown fires [6]

A recent paper add further examples of this fire-driven trait divergence: Vandvik et al. show that smoke-induced germination is observed in populations of Calluna vulgaris (Ericaceae) from traditionally burnt coastal heathlands of Norway but it is lacking in populations from other habitats with infrequent fires [7]. The results are also consistent with the suggestion that smoke-induced germination is a fire adaptation [8-9].

Calluna-smoke-germination

Figure: Probability of germination of Calluna vulgaris in relation to time (days) since sowing for smoke-treated (pink) and control (grey) seeds, in coastal and inland heathlands of Norway. From Vandvik et al. 2014 [7].

References:

[1] Pausas, J. G. and D. W. Schwilk. 2012. Fire and plant evolution. New Phytologist 193 (2). [doi | pdf | blog]

[2] Gómez-González S, Torres-Díaz C, Bustos-Schindler C, Gianoli E, 2011. Anthropogenic fire drives the evolution of seed traits. PNAS 108: 18743-18747. [doi blog]

[3] Pausas J.G., Alessio G., Moreira B. & Corcobado G. 2012. Fires enhance flammability in Ulex parviflorusNew Phytologist 193: 18-23. [doi | pdf | blog]

[4] Pausas J.G. & Moreira B. 2012. Flammability as a biological concept. New Phytologist 194: 610-613. [doi | wiley | pdf]

[5] Moreira B., Castellanos M.C., Pausas J.G. 2014. Genetic component of flammability variation in a Mediterranean shrub. Molecular Ecology 23: 1213-1223. [doi | pdf | suppl. | data:dryad | blog]

[6] Hernández-Serrano A., Verdú M., González-Martínez S.C., Pausas J.G. 2013. Fire structures pine serotiny at different scales. American Journal of Botany 100 (12): 2349-2356. [doi | amjbot | pdf | supp. | blog]

[7] Vandvik, V., J. P. Töpper, Z. Cook, M. I. Daws, E. Heegaard, I. E. Måren, and L. G. Velle. 2014. Management-driven evolution in a domesticated ecosystem. Biology Letters 10 (2): 20131082. [doi]

[8] Pausas J.G. & Keeley J.E. 2009. A burning story: The role of fire in the history of life. BioScience 59: 593-601 [doi | jstor | BioOne | pdf | scribd | ppt slides | post]

[9] 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(8): 406-411. [doi | trends | pdf]

 

Serotiny

November 16th, 2013 No comments

Serotiny is the delayed seed release for more than a year by retaining the seeds in a woody structure [1]. This implies an accumulation of a canopy seed bank. Serotiny confer fitness benefits in environments with frequent crown-fires, as the heat opens the cones and seeds are dispersed in the post-fire bed which is rich in resource and the competition and predation are low. It is typical of many Proteaceae and some conifers, like some pine species [1, 2; figure below].

Two recent papers analyse the serotiny of two mediterranean pines Pinus halepensis and Pinus pinaster [3, 4]. P. halepensis show higher proportion of serotinous cones than P. pinaster, but the latter retain the cones for longer [3]. The two species show high variability of serotiny within and between populations, but they show a clear pattern of higher serotiny in populations subject to high frequency of crown-fires than those living in areas where crown-fires are rare or absent. This is true either considering serotiny as the proportion of serotinous cones or as the age of the cones stored. Compared with other pines worldwide, the strength of the fire-serotiny relationship in P. pinaster is intermediate, and in P. halepensis is among the highest known [3]. For P. halepensis (the species with higher % serotiny), populations in high fire recurrence regimes have higher fine-scale spatial aggregation of serotiny than those inhabiting low fire recurrence systems. This phenotypic spatial structure generated by fire could be a consequence of the spatial genetic structure of the population. The second study used genomic tools to search for a genetic association for serotiny [4]. The analysis of 384 SNPs of 199 individuals of P. pinaster (in 3 populations included in the previous study [3])  shows that 17 loci were associated with serotiny and explain all together ca. 29% of the serotiny variation found in the field. All these results adds further evidence to the emerging view that fire shapes intraspecific variability of traits and generates phenotypic divergence between populations [5, 6, 7].

Figure: Serotinous cones of Pinus pinaster (Foto: K.B. Budde)

References:

[1] 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]

[2] He T, Pausas JG, Belcher CM, Schwilk DW, Lamont BB. 2012. Fire-adapted traits of Pinus arose in the fiery Cretaceous. New Phytologist 194: 751-759. [doi | wiley | pdf (suppl.)]

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

[4] Budde, K. B., Heuertz, M., Hernández-Serrano, A., Pausas, J.G., Vendramin, G.G., Verdú, M. & González-Martínez, S.C. 2014. In situ genetic association for serotiny, a fire-related trait, in Mediterranean maritime pine (Pinus pinaster Aiton). New Phytologist  201: 230-241 [doi | pdf]

[5] 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(8): 406-411. [doi] [trends] [pdf]

[6] Pausas, J. G., Schwilk, D. W. 2012. Fire and plant evolution. New Phytologist, 193:301-303. [doi | wiley | pdf]

[7] Pausas J.G., Alessio G., Moreira B. & Corcobado G. 2012. Fires enhance flammability in Ulex parviflorusNew Phytologist 193: 18-23. [doi | wiley | pdf]

 

Afrotropical and neotropical savannas are different

July 29th, 2013 No comments

Savannas are typically ecosystems dominated by grasses with a variable tree density (e.g., [1]). However, the savanna biome is very large, it occurs in different continents, and includes a large variability in the vegetation structure and composition. Fire and herbivory are the main disturbance factors shaping savannas worldwide and because the different climatic conditions and the different evolutionary histories among different savannas, fire and herbivory regimes also varies among savannas. Because plants are not adapted to fire and herbivory “per se” but to specific regimes of herbivory and fire [2], we expect different strategies to cope with these disturbances in different savannas. In this framework, we have recently compared savannas from Africa and from South America (afrotropical and neotropical savannas respectively) [3]: Afrotropical savannas have a dryer climate and are more intensely grazed than neotropical savannas, and thus the amount of available fuel is typically lower in afrotropical than in the neotropical savannas. Consequently fires tend to be more intense in neotropical savannas. In afrotropical conditions, young woody plants tend to grow quickly in height to soon locate the canopy above the flame zone before the next fire, and above the browsing height. Thus these plants tend to have a pole-like or lanky architecture (the lanky strategy). In contrast, in neotropical savannas where herbivory pressure is lower they require a thick corky bark for protection against relatively intense fires (the corky strategy) [3]. Despite the two fire escape strategies appear in both Africa and South America, we suggest that the lanky strategy is more adaptive in afrotropical savannas, while the corky strategy is more adaptive in neotropical savannas [3].


Figure: Diospyros hispida A.DC. (Ebenaceae), a South American example of a plant with the corky strategy. Although the trunk was fully burned one year earlier (dark branches and trunk), the bark protected the lateral buds which enabled epicormic resprouting and the formation of lateral resprouts (light grey branches). This photo was taken in Emas National Park (cerrado ecosystem, Brazil) at the beginning of the rainy season (2011) when this deciduous plant starts to produce new leaves (Photo: V.L. Dantas). For an example of the lanky strategy see [4].

References:
[1] Dantas V., Batalha, MA & Pausas JG. 2013. Fire drives functional thresholds on the savanna-forest transition Ecology 94:2454-2463. [doi | pdf | blog]

[2] 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 Plant Sci. 16(8): 406-411. [doi | trends | pdf]

[3] Dantas V. & Pausas J.G. 2013. The lanky and the corky: fire-escape strategies in savanna woody species Journal of Ecology 101: 1265-1272 [doi | pdf]

[4] Archibald, S. & Bond, W.J. 2003. Growing tall vs growing wide: tree architecture and allometry of Acacia karoo in forest, savanna, and arid environments. Oikos, 102: 3-14.

 

A new global fire map

March 6th, 2013 2 comments

We have used remotely sensed fire information for the whole globe and aggregated this information by the WWF ecoregions, to produce an ecologically-based global fire map (figure below [1]). Using this map we have tested the intermediate fire-productivity model [2,3], i.e. that fire activity changes along the productivity/aridity gradient following a humped relationship. The results suggest that fires occur in all biomes and in nearly all world ecoregions. Fire activity peaked in tropical grasslands and savannas, and significantly decreased towards the extremes of the productivity gradient. Both the sensitivity of fire to high temperatures and the above-ground biomass increased monotonically with productivity. In other words, fire activity in low-productivity ecosystems is not driven by warm periods and is limited by low biomass; in contrast, in high-productivity ecosystems fire is more sensitive to high temperatures, and in these ecosystems, the available biomass for fires is high. The results support the intermediate fire–productivity model on a global scale and suggest that climatic warming may affect fire activity differently depending on the productivity of the region. Fire regimes in productive regions are more vulnerable to warming (drought-driven fire regime changes), while in low-productivity regions fire activity is more vulnerable to fuel changes (fuel-driven fire regime changes [4]).

Figure: An ecologically-based global fire map, from Pausas & Ribeiro (2013) [1]. The shape file is available under request [email here].

References
[1] Pausas J.G. & Ribeiro E. 2013. The global fire-productivity relationship. Global Ecol. & Biogeogr. 22: 728-736 [doi | pdf | erratum] – UPDATE: Paper featured by NASA.

[2] Pausas J.G. & Paula S. 2012. Fuel shapes the fire-climate relationship: evidence from Mediterranean ecosystems. Global Ecol. & Biogeogr. 21: 1074-1082. [doi | pdf | supp]

[3] Pausas J.G. & Bradstock R.A. 2007. Fire persistence traits of plants along a productivity and disturbance gradient in Mediterranean shrublands of SE Australia. Global Ecol. & Biogeogr. 330-340. [pdf | doi]

[4] 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 |  pdf]