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]

NASA and Fire ecology

November 28th, 2014 No comments

NASA has featured our paper on the global fire-productivity relationship [1] in NASA Sensing Our Planet 2014

strange-bedfellows

 

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

[2] Vizcarra N. 2014. Strange bedfellows. NASA Sensing Our Planet 2014 [link | PDF]

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.

 

Trait databases: BROT to EOL

October 26th, 2014 No comments

Some years ago we complied and published a database on plant traits related to fire for the Mediterranean basin, the BROT database [1, 2]. Now the Encyclopedia of Life (EOL, eol.org), which is an initiative to gather scientific knowledge about all animal and plant life on Earth, has incorporated the BROT database [link]! We are very happy that EOL consider BROT as a reliable source of information; this implies that our compilation effort is now much more widely accessible, with a friendly interface, and integrated with other sources of information. For instance, if you search a Mediterranean plant species in the EOL search engine (e.g., Cistus albidus), you get, a part from pictures, a description, and other details, a window with the trait information extracted from BROT (see the overview result here; you can also go to the full trait data). It is aslo possible to search by trait in all EOL databases (eol.org/traitbank). Note however that we were not responsible for translating the BROT database to the EOL format, so any error or misinterpretation during this process is not our fault! In fact we have never been asked or notified that EOL was going to incorporate BROT, I found it just by chance …

eol

References:

[1]  Paula S, Arianoutsou M, Kazanis D, Tavsanoglu Ç, Lloret F, Buhk C, Ojeda F, Luna B, Moreno JM, Rodrigo A, Espelta JM, Palacio S, Fernández-Santos B, Fernandes PM, and Pausas JG. 2009. Fire-related traits for plant species of the Mediterranean Basin. Ecology 90: 1420. [doi] [ESA journals] [Ecological Archives E090-094] [pdf]

[2] Paula S. & Pausas J.G. 2013. BROT: a plant trait database for Mediterranean Basin species. Version 2013.06. URL: http://www.uv.es/jgpausas/brot.htm

 

Heritability of serotiny

September 29th, 2014 No comments

Evolution by mean of natural selection requires three conditions: there is variation in the trait, this variation is linked to differences in fitness, and the variation is heritable (Darwin!). In many traits we do not have reliable information for the three processes. For a serotinous species, there is evidence that the level of serotiny is variable, and specially it varies in relation to the fire regime of the population. This is because serotiny increases fitness in crown-fire ecosystems and it is not advantageous in ecosystems that do not suffer frequent fires or in ecosystems with understory fires. We recently studied how serotiny of two pine species (Pinus halepensis and Pinus pinaster) varies within population and between populations with different fire regimes and also provided a meta-analysis of the relation between serotiny and fire from other published studies [1]. We also performed a genetic association study for serotiny using SNPs and showed that 17 loci explained ca. 29% of the serotiny variation found in the field in Pinus pinaster [2], suggesting that serotiny variation have a genetic basis. In our most recent paper we provide the first estimate of heritability for a fire trait; specifically we computed the norrow-sense heritability (h2) of serotiny in Pinus halepensis using the common garden approach [3]. We also evaluated whether fire has left a selection signature on the level of serotiny among populations by comparing the genetic divergence of serotiny with the expected divergence of neutral molecular markers (QST – FST comparison). Serotiny showed a significant heritability (h2 = 0.20). The quantitative genetic differentiation among provenances for serotiny (QST= 0.44) was significantly higher than expected under a neutral process (FST = 0.12), suggesting adaptive differentiation. Overall we showed that serotiny is a heritable trait and that it has been shaped by natural selection driven by fire.

ph-serotiny
Figure: Serotinous cones of Pinus halepensis (Foto: J.G. Pausas)

References:

[1] 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]

[2] 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 | supp1 | supp2]

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

 

The Fire Ecology journal now on JCR

August 22nd, 2014 No comments

The journal Fire Ecology (FE) has now been included in the Journal Citation Reports database (2013 JCR Edition, ISI) and thus, it has an Impact Factor. The 2013 impact factor is 1.156 which suggests that it is still a very minor ecology journal (ranking: 28/64 in Forestry and 104/140 in Ecology) but given that it is of open access, it has some potential for increasing success. For comparison, the International Journal of Wildland Fire, which is a more multidisciplinary journal for fire science has an IF= 2.506 (ranking = 5/64 in Forestry); other classical ecology journals have a much higher impact factor (e.g., Journal of Ecology: 5.69, Ecology: 5.00, Oikos: 3.56, Oecologia: 3.25). The FE journal is still very USA-oriented, and a strong internationalization would be needed. The last issue of the journal is also available at ISSUU, so it can be read it from Android systems. I must admit I have never published or submitted any paper to this journal (see details). Good luck to the FE in this new period!

FireEcol-journal

Journal archive in the web site of the Fire Ecology journal [link]

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]

 

Vive la différence!

April 20th, 2014 No comments

This post is a bit off the main topics of this blog, but I found an interesting study that I would like to share [1]. Using virtual reality tools, the authors of this study performed an experiment placing white people with a body of black people for about 12 minutes. They compared the results of a test for racial bias performed few days before the experiment with the results of the same test performed after the experiment, and found a clear reduction in the scores! I guess virtual reality could be a tool to increase empathy, and therefore respect to the difference. So perhaps racism is curable!

colours-variability_sm

Figure:  Team of happy people working together (www.dreamstime.com; top left), variability of the Cuban Polymita (top right) and variability of the Harlequin ladybird (Harmonia axyridis; bottom; source).

References
[1] Peck TC, Seinfeld S, Aglioti SM, Slater M. 2013. Putting yourself in the skin of a black avatar reduces implicit racial bias, Consciousness and Cognition, 22, 779-787. [doi].  More virtual experiments at: http://presence-thoughts.blogspot.com.es

 

Postfire blooming of Asphodelous

April 5th, 2014 No comments

The 4th of February, 2014, a forest fire burnt ca. 200 ha in Segorbe, near Valencia, eastern Spain. Two months later (1st April 2014), few plants had started to resprout, others had started to germinate, but there were three species that had resprouted very quickly and were already flowering: Asphodelous cerasiferus (= A. ramosus; Spanish: gamón), Iris lutescens, and Asparagus horridus; the first showed an spectacular blooming (pictures below).

Asphodelus-bloom
Spectacular postfire bloom of Asphodelous cerasiferus in Segorbe, near Valencia, Spain (photos by MC Castellanos & JG Pausas, two months after fire).

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]

 

New fire books

March 23rd, 2014 No comments

Two new fire books has been recently published! And both have a global and interdisciplinary perspective. The first is edited by Claire Belcher (2013; [1]), and each of the 16 chapters is a scientific article written by different specialists (a total of 25 different authors, many of them from UK institutions); it includes few colour plates. As the publisher says, “the book shows how knowledge of fire phenomena and the nature of combustion of natural fuels can be used to understand modern wildfires, interpret fire events in the geological record and to understand the role of fire in a variety of Earth system processes ”. This book has perhaps little on fire ecology, and it is more focussed on fire history at the geological scale, combustion details and atmospheric impacts; all these topics are important for understanding fires at the global scale. The second book (Scott et al. 2014; [2]) is a full-colour textbook on fire written by five authors (two of them had also participated in the other book). This is probably the first general textbook on fire science ever published, and as such it covers all topics related to fire although with relatively little depth. Thus it provides a summary of the current knowledge on fire at a global scale. In the words of the publisher, it “is designed to provide a synthesis of contemporary thinking; bringing together the most powerful concepts and disciplinary voices to examine, in an international setting, why planetary fire exists, how it works, and why it looks the way it does today”.

firebookscover

[1] Belcher, C.M. (ed) 2013. Fire Phenomena and the Earth System: An Interdisciplinary Guide to Fire Science. Wiley.

[2] Scott, A.C., Bowman, D.M.J.S., Bond, W.J., Pyne, S.J. & Alexander, M.E. 2014. Fire on Earth: An Introduction. Wiley.

New fire book in 2012: link

 

Proyecto VIRRA

February 28th, 2014 No comments

El proyecto “El papel del fuego en la Variabilidad Intraespecífica (fenotípica y genética) de plantas del matoRRAl mediterráneo (VIRRA)” finalizó hace unos meses. Aquí se puede ver un resumen y los principales productos de este proyecto: enlace.

Ulex parviforus_juli_sm

La aliaga (Ulex parviflorus) es una de las principales especies estudiadas en VIRRA [1, 2].

[1] Ulex born to burn, jgpausas.blogs.uv.es, 9/Nov/2011

[2] Ulex born to burn (II): genetic basis of plant flammability,  jgpausas.blogs.uv.es, 25/Jan/2014

Ulex born to burn (II): genetic basis of plant flammability

January 25th, 2014 No comments

In an previous study we found that Ulex parviflorus (Fabaceae) populations that inhabit in recurrently burn areas (HiFi populations) were more flammable than populations of this species growing in old-fields where the recruitment was independent of fire (NoFi populations) [1,2, 3]. That is, HiFi plants ignited quicker, burn slower, released more heat and had higher bulk density than NoFi plants. Thus, it appeared that repeated fires selected for individuals with higher flammability, and thus driving trait divergence among populations living in different fire regimes. These results were based on the study of plant flammability (phenotypic variability) without knowing whether plant flammability was genetically controlled. In a recent study using the same individuals [4], we show that phenotypic variability in flammability was correlated to genetic variability (estimated using AFLP loci) [figure below]. This result provide the first field evidence supporting that traits enhancing plant flammability have a genetic component and thus can be responding to natural selection driven by fire [5]. These results highlight the importance of flammability as an adaptive trait in fire-prone ecosystems.

Ulex-flam-AFLP

Figure: Relationship between flammability and genotypic variability at individual level in Ulex parviflorus (red symbols: individuals in HiFi populations; green symbols: individuals in NoFi populations). Variations in flammability are described using the first axis of a Principal Component Analysis (PCA1) performed from different flammability traits, and genetic variability is described using the first axis of a Principal Coordinate Analysis (PCo1) from the set of AFPL loci that were significantly related to flammability. See details in [4].

References
[1] Ulex born to burn, jgpausas.blogs.uv.es, 9/Nov/2011

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

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

[4] 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 | data:dryad]

[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: 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]

 

Physiological differences between resprouters and seeders

November 9th, 2013 No comments

The ability to resprout and to recruit after fire are two extremely important traits for the persistence in fire-prone ecosystems [1,2], and they define three life histories: obligate resprouters, obligate seeders (non-resprouters), and facultative seeders. After a fire, obligate seeders die and recruit profusely from the seeds stored in the seed bank [3-5]. In contrast, resprouters survive after fire and their above-ground tissues regenerate from protected (often below-ground) buds by using stored carbohydrates [6]. Facultative seeders not only recruit profusely after fire, but are also able to resprout. In fact, seeders and resprouters have different regeneration niches: seedling regeneration of obligate resprouters is not linked to fire, and they recruit during the inter-fire period under sheltered conditions (i.e., under vegetation cover), while seedling regeneration of seeders occurs in open postfire environments. Given the marked difference in water availability between microsites under vegetation and microsites open to the sun under Mediterranean conditions, seedlings of resprouters and seeders are subjected to different water-stress conditions, and thus they are expected to have different physiological attributes. Despite these differences, resprouters and seeders co-exist, are often well-mixed on local and landscape scales [7,8], and represent the two main types of post-fire regeneration strategies in Mediterranean ecosystems [2].

A recent study demonstrates marked differences in physiological attributes between seedlings of seeders and resprouters [9]: Seeders show a range of physiological traits that better deal with water-limited and highly variable conditions (e.g., higher resistance to xylem cavitation, earlier stomatal closure with drought, higher leaf dehydration tolerance), but they are also capable of taking full advantage of periods with high water availability (greater efficiency in conducting water through the xylem to to sustain high gas exchange rates when water is available). Conversely, resprouter species are adapted to more stable water availability conditions, favoured by their deeper root system, but they also display traits that help them resist water shortages during long summers.

Previous studies already showed marked differences between seeders and resprouters in a range of attributes: resprouters tend to exhibit a deeper root-system, while seedling root structure of seeders are more efficient in exploring the upper soil layer [10]. Leaves of seeders show higher water use efficiency (WUE) and higher leaf mass per area (LMA; i.e., higher sclerophylly, lower SLA) [11]. Seeds of seeder species are more tolerant to heat shocks and have greater heat-stimulated germination [3]. All these differences support the idea that they are distinct syndromes with different functioning characteristics at the whole plant level and suggest that they undertook different evolutionary pathways [12].

Figure: Coexistence of resprouters (R+) and seeders (R-) in postfire conditions near Valencia, Spain. (Foto: A. Vilagrosa).

 

References:

[1] Pausas, J.G., Bradstock, R.A., Keith, D.A., Keeley, J.E. & GCTE Fire Network. 2004. Plant functional traits in relation to fire in crown-fire ecosystems. Ecology 85: 1085-1100. [jstor |[pdf | Ecological Archives E085-029]

[2] 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]

[3] Paula S. & Pausas J.G. 2008. Burning seeds: Germinative response to heat treatments in relation to resprouting ability. Journal of Ecology 96 (3): 543 – 552. [doi | pdf]

[4] Moreira B., Tormo J., Estrelles E., Pausas J.G. 2010. Disentangling the role of heat and smoke as germination cues in Mediterranean Basin flora. Annals of Botany 105: 627-635. [doi | pdf | blog]

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

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

[7] Verdú M, & Pausas JG 2007. Fire drives phylogenetic clustering in Mediterranean Basin woody plant communities Journal of Ecology 95 (6), 1316-323 [doi | pdf]

[8] Ojeda, F., Pausas, J.G., Verdú, M. 2010. Soil shapes community structure through fire. Oecologia 163:729-735. [doi | pdf | blog]

[9] Vilagrosa A., Hernández E.I., Luis V.C., Cochard H., Pausas, J.G. 2014. Physiological differences explain the co-existence of different regeneration strategies in Mediterranean ecosystems. New Phytologist 201 : xx-xx [doi | pdf | suppl.] – NEW

[10] Paula S. & Pausas J.G. 2011. Root traits explain different foraging strategies between resprouting life histories. Oecologia 165:321-331. [doi | pdf | blog]

[11] Paula S. & Pausas J.G. 2006. Leaf traits and resprouting ability in the Mediterranean basin. Functional Ecology 20: 941-947. [doi | pdf | blog]

[12] Verdú M. & Pausas J.G. 2013. Syndrome-driven diversification in a Mediterranean ecosystem. Evolution 67: 1756-1766. [doi | pdf | blog]

 

Towards prescribed fires

October 7th, 2013 No comments

In the latest issue of Science (Oct 4th, 2013), there is a forum paper with some suggestion for the management of fires and forests in the face of changing climates [1]. Basically, the authors suggest that policy focused on fire suppression only delays the inevitable, promising more dangerous and destructive forests fires. They emphasize the importance of strategically managing wildfires and the use of prescribed fires in combination with mechanical fuel treatments to create fire resilient landscapes. In addition, the journal Frontiers in Ecology and Environment has recently published an special issue on prescribed burns in different ecosystems worldwide [2]. Fires are very important processes on many ecosystems [3,4], and what is important is to shape fire regimes to be sustainable (socially and ecologically). A zero-tolerance fire policy (which still dominates in many countries) cannot work in the long-term, especially in seasonal climates, as the high fuel accumulation coupled with a warming climate may drive the system to large and intense fires that threaten both people and biodiversity; and this may occurs despite major economic investments in fire prevention and suppression.


Foto: Prescribed understory burn of a mixed conifer forest in the Sierra Nevada, California. From [3].

References:
[1] Stephens, S.L., Agee, J.K., Fulé, P.Z., North, M.P., Romme, W.H., Swetnam, T.W., Turner, M.G., 2013. Managing forests and fire in changing climates. Science 342, 41-42.

[2] Perspectives on prescribed burning. Front. Ecol. Environ. 11, www.esajournals.org/toc/fron/11/s1

[3] Pausas J.G. & Keeley J.E. 2009. A burning story: The role of fire in the history of life. BioScience 59: 593-601 [doi | pdf]

[4] 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]

 

Smoke-stimulated recruitment

September 16th, 2013 No comments

In many plant species from mediterranean ecosystems, germination is promoted by fire [1]; this effect may be driven by the heat [e.g., 2-4] or by the chemicals produced by the fire (e.g., smoke, 4,5]). Most information regarding to smoke-stimulated germination in the Mediterranean Basin comes from a few experiments performed in laboratory conditions. This approach does not consider factors that occur in the field, such as species interactions, density-dependent processes or the fact that seeds spent time in the soil. A recent field experiment performed in eastern Spain show that smoke increase overall seedling recruitment, specially seedlings of annual plant species [6]. However, despite most species had higher seedling establishment in the smoke than in the control subplots, there were very few species in which the effect of smoke was statistically significant, suggesting that the community response to smoke cannot be inferred from individual species; it is the sum of small differences in each species towards the same direction that produces a significant pattern at community scale. This emerging property of the community is often neglected by only considering germination experiments in the laboratory. The results also suggest that the effect of smoke in annual species of the Mediterranean Basin might be more relevant than previously thought.

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] Paula S. & Pausas J.G. 2008. Burning seeds: Germinative response to heat treatments in relation to resprouting ability. Journal of Ecology 96 (3): 543 – 552. [pdf | doi]

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

[4] Moreira B., Tormo J., Estrelles E., Pausas J.G. 2010. Disentangling the role of heat and smoke as germination cues in Mediterranean Basin flora. Annals of Botany 105: 627-635. [pdf | doi | post]

[5] Smoke-stimulated germination, jgpausas.blogs.uv.es, 2/Dec/2011.

[6] Tormo, J., B. Moreira, and J. G. Pausas. 2014. Field evidence of smoke-stimulated seedling emergence and establishment in Mediterranean Basin flora. Journal of Vegetation Science 25: 771-777 [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.

 

Incendios del 2012 en Valencia: una año después

June 28th, 2013 4 comments

Hace ahora un año dos grandes incendios, prácticamente simultáneos y cerca de la ciudad de Valencia, conmocionaron a la población. El incendio de Andilla-Alcublas afectó unas 21 000 ha y el de Cortes de Pallás-Dos Aguas unas 30 000 ha; raramente se dan incendios de estas dimensiones. Gracias a la extrema capacidad de las plantas y animales para recuperarse de estos eventos, un año después vemos el paisaje verde y lleno de vida (Fig. 1). En la zona afectada por los incendios se observa un gran número de plantas en flor, así como elevada actividad de animales (insectos polinizando, lagartijas, eslizones, serpientes, etc.). La sensación es una buena recuperación, a excepción de algunas de las zonas donde se está extrayendo los árboles quemados. Durante el primer año después de un incendio el suelo es relativamente frágil, de manera que entrar con máquinas o arrastrar troncos, puede reducir la regeneración natural y aumenta la probabilidad de erosión del suelo, especialmente en zonas con elevada pendiente (Fig. 2). Además, el dejar los árboles muertos en pie favorece las condiciones microclimáticas para la vegetación, genera hábitat para infinidad de invertebrados y sirve de posadero para aves que defecan y dejas semillas que también ayudan a la regeneración (efecto percha).


Fig. 1. Diversas imágenes tomadas a principios de junio 2013, casi un año después de los incendios, en Andilla y Cortes.
 
 

Fig. 2. Zona donde se está extrayendo la madera quemada, al oeste del incendio de Cortes-Dos Aguas (Junio 2013).
 

Información adicional

Life 15 days after the large fires in Valencia. jgpausas.blogs.uv.es 22/7/2012

Incendios forestales en Valencia, Junio 2012. jgpausas.blogs.uv.es 4/7/2012

De incendios y cipreses,  (1) jgpausas.blogs.uv.es 29/9/2012,  (2) jgpausas.blogs.uv.es 7/10/2012,  (3) jgpausas.blogs.uv.es 22/6/2013

Incendios forestales, una visión desde la ecología
 

De incendios y cipreses (3)

June 22nd, 2013 3 comments

Ha llegado el verano y con ello el riesgo de incendios forestales. En los medios de comunicación de España vuelven a salir noticias sobre las bondades de los cipreses para reducir los incendios. Hace unos días  (el 17 Junio 2013) en la portada del diario Levante (Valencia) se leía “La diputación de plantará cipreses en Los Serranos para que actúen de barrera contra los incendios”.  Similares mensajes se publican en otros medios (Los cipreses reducen el avance de un incendio forestal, Un estudi assegura que els xiprers poden servir per reduir l’avanç dels incendis forestals, etc…). Todos estos mensajes se basan en el hecho que el año pasado en el incendio ocurrido en Andilla-Alcublas había una plantación de cipreses que no se vio afectada por el fuego, y se extendió el falso mensaje de que los cipreses podían ser “ignífugos” [1]. Ya hablamos en su día de que los cipreses de esa plantación no se quemaron, básicamente porque están rodeados de un cortafuegos, y así se puede ver en las fotografías y detalles que presenté el año pasado (ver detalles en [ 2 ] y [ 3 ] ).

Además, un estudio reciente analiza en el laboratorio la inflamabilidad de ramitas de ciprés [4], y las conclusiones son claras; textualmente: “Regarding the flammability of its live leaves, Cupressus sempervirens was not very flammable; however, because this species had the greatest amount of dead material which was ranked extremely flammable, this ornamental species should be avoided in wildland-urban interface, especially close to houses“. En decir, que aunque las hojas verdes del ciprés se pueden considerar relativamente poco inflamables, este árbol suele acumular ramas secas que son muy inflamables y por lo tanto representan un peligro para los incendios. Estas conclusiones son coherentes con el hecho de que en algunos países está prohibido plantar cipreses en jardines de casas que lindan con el monte, precisamente por su peligro con los incendios. En otras palabras, no hay ninguna base que apoye la idea de que los cipreses puedan ser útiles para la lucha contra los incendios, e incluso podrían ser contraproducentes. Por lo tanto no se entiende la decisión de la Diputación de Valencia de plantar cipreses en los montes valencianos. Además, los cipreses no son naturales de esta tierra, con lo que contribuyen a degradación de nuestro paisaje.

 

Referencias
[1] Los cipreses se comportan como escudos naturales contra el fuego. El País, Valencia, 9/7/2012

[2] De incendios y cipreses (1), jgpausas.blogs.uv.es 29/9/2012

[3] De incendios y cipreses (2), jgpausas.blogs.uv.es 7/10/2012

[4] Ganteaume A, Jappiot M, Lampin C, Guijarro M & Hernando C. 2013. Flammability of some ornamental species in wildland–urban interfaces in southeastern France: laboratory assessment at particle level. Environmental Management [doi]

[5] Incendiso forestales en Valencia, Junio 2012, jgpausas.blogs.uv.es 4/7/2012

 

Fire-stimulated flowering

May 25th, 2013 No comments

Some plant species flower profusely and quickly after fire (fire-stimulated flowering). Compared with resprouting or postfire seeding, this trait is relatively unknown outside of South Africa and Australia [1, 2]. It is considered one of the adaptations of some resprouting species to live in recurrently burn environments. There are some of these species that rarely flower without a fire (obligate postfire flowering) while others can flower in the absence of fire but they produce more flowers after it (facultative postfire flowering). One example I had the chance to observe recently in Central America is Bulbostylis paradoxa (Cyperaceae; Figure below); it is a very flammable plant that grow in savannas and dry forest of Central/South America and the Caribbean. Local foresters told me that they have never seen this species flowering in absence of fire, and that they start flowering next day after the fire.


Figure: Bulbostylis paradoxa (Cyperaceae) one month after a fire in Santa Rosa National Park, Costa Rica (fotos: J.G. Pausas, May 2013).

References:
[1] Bytebier B., Antonelli A., Bellstedt D.U., Linder H. P. 2011. Estimating the age of fire in the Cape flora of South Africa from an orchid phylogeny. Proc. R. Soc. B, 278: 188-195.

[2] Lamont B.B., Downes K.S. 2011. Fire-stimulated flowering among resprouters and geophytes in Australia and South Africa. Plant Ecol. 212: 2111-2125.

 

Fire shapes savanna-forest mosaics in the Brazilian cerrado

May 14th, 2013 No comments

Cerrado is the name of a tropical fire-prone mosaic of savanna and forest in Brazil. In a recent paper [1], we showed that in cerrado landscapes, despite the existence of a great variety of community structure (from open savannas to closed forests; Figure below), there are two well-defined stable states of community function, each associated with contrasting levels of community closure (open and closed environments) and maintained by different fire regimes. Soil properties, phylogenetic and non-phylogenetic beta-diversities, and most of the plant functional traits presented a threshold pattern along the community closure gradient with coinciding breakpoints, providing strong evidence of a functional threshold along the forest-savanna gradient. Open environments consisted of communities growing on poor soil and dominated by short species with early investments in thick barks, low wood density and with thick and tough leaves (high toughness and low specific area). In contrast, closed communities grow in more fertile soils and include plants having the opposite functional attributes. Moreover, we found contrasting fire regimes on the two sides of the threshold, with open formations showing shorter fire intervals than closed formations and a switch from communities dominated by fire-resistant plants to communities dominated by shade tolerant species that compensate for their lack of fire resistance by efficiently closing the canopy (i.e., reducing flammability). Overall, these results are consistent with the theoretical model of fire-plant feedbacks as main drivers of the coexistence of two stable states, savanna and forest. In this context, we provide the first field-based evidence for a community-level threshold separating two vegetation states with distinct functional and phylogenetic characteristics and associated with different fire regimes.

Top: A woodland cerrado (cerrado sensu stricto) six months after a fire, with several top-killed trees and a developed layer of resprouting vegetation; and one of the sampled closed forests.
Middle: A dense woodland cerrado (cerrado denso); one example of a typical thick-barked species found in open communities (Anadenanthera peregrina (Benth.) Reis, Fabaceae); a transitional zone between dense savannas and forests.
Bottom: A typical open savanna at the early rainy season, with tall flammable grasses and small trees and shrubs.
Photo credits: V. Dantas, G. Sartori, V. Cadry, J.G. Pausas, F. Noronha, A. Favari. See [1].

References

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

 

Art: fire by Chema Madoz

March 19th, 2013 No comments

I have recently visited a very nice and impressive exhibition of photographs by Chema Madoz; his photographs are visual poems. Here one that deals with fire.

A new global fire map

March 6th, 2013 No 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].

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

[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]

 

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