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Valencia, Spain

Functional Ecology

Bark is a vital and very visible part of woody plants, yet only recently has bark characteristics started to be considered as key traits structuring communities and biomes. Bark thickness is very variable among woody plants, and I hypothesize that fire is a key factor selecting for a thick bark, and thus, at the global scale, a significant proportion of the variability in bark thickness is explained by the variability in fire regimes. Previous research has focused on the importance of bark thickness mainly in surface-fire regimes; here I generalize this idea and present a conceptual framework to explain how the different drivers that affect fire intensity have shaped bark thickness, in conjunction with other plant traits. I first review methods used to study bark thickness and then provide examples of bark thickness patterns from a wide range of ecosystems subject to different fire regimes (understorey fires, grass-fuelled surface fires, grass-fuelled crown fires and infrequent fires). There are some fire regimes that select for thick barks, while some only in the base of the trunk (e.g. understorey fires), others select for a thick bark on the whole plant (e.g. grass-fuelled crown fires). There are also fire regimes in which allocating resources to a thick bark is not adaptive (e.g. woody-fulled crown fires). Fire regime 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; however, the current paucity of data limits a fully accurate analysis. © 2014 The Authors. Source

Dantas V.D.L.,Federal University of Sao Carlos | Pausas J.G.,CIDE CSIC
Journal of Ecology

Fire and herbivory are the main disturbances shaping the structure of savannas. In these ecosystems, the key strategies by which woody plants escape fire are either early height growth (the lanky strategy) or early bark growth (the corky strategy). We hypothesize that the dominance of each strategy in different savannas depends on the prevailing disturbance regimes. Given the importance of herbivory in afrotropical savanna, we expect woody plants in these savannas to be taller and have thinner barks (the lanky strategy) than plants in neotropical savanna where fire tends to be more intense (the corky strategy). We compiled data on bark thickness and stem height in relation to stem diameter for afrotropical and neotropical savanna woody species and tested for differences in the allometric relationship between these two savannas with a general linear mixed model (GLMM). Fire intensities were higher in neotropical than in afrotropical savannas. Afrotropical savanna plants were taller and had thinner barks for a given diameter than neotropical savanna plants - supporting our hypothesis that because of the contrasting disturbance regimes, the lanky strategy is more adaptive in afrotropical savannas, whereas the corky strategy is more adaptive in neotropical savannas. Synthesis. While the lanky strategy is more associated with heavily browsed and fuel-controlled savannas, the corky strategy is associated with lightly browsed savannas that experience more intense fires. Because the relative role of disturbances varies across the globe, we suggest that the height-bark-diameter scheme is a powerful framework for understanding the ecology of many savannas. In savanna ecosystems there are two main strategies to scape fire. The lanky strategy (early alocation to height) is more associated with heavily-browsed and fuel-controlled savannas, while the corky strategy (early allocation to a thick bark) is associated with lightly-browsed savannas that experience more intense fires. Because the relative role of disturbances varies across the globe, we suggest that the height-bark-diameter scheme is a powerful framework for understanding the ecology of many savannas. © 2013 British Ecological Society. Source

Trends in Plant Science

Microevolutionary studies show that fire traits are variable within and among populations, especially among those subject to different fire regimes. In addition, there is increasing evidence of an inherited genetic basis to variability in fire traits. Added together, pines provide compelling evidence that fire can exert an evolutionary pressure on plants and, thus, shape biodiversity. In addition, evolutionary fire ecology is providing insights to improve the management of pine forests under changing conditions. The lessons learned from pines may guide research on the evolutionary ecology of other taxa. © 2015 Elsevier Ltd. Source

Dantas V.d.L.,Federal University of Sao Carlos | Pausas J.G.,CIDE CSIC | Batalha M.A.,Federal University of Sao Carlos | de Paula Loiola P.,Federal University of Sao Carlos | Cianciaruso M.V.,Federal University of Goais

Intraspecific trait variability plays a fundamental role in community structure and dynamics; however, few studies have evaluated its relative importance to the overall response of communities to environmental pressures. Since fire is considered a key factor in Neotropical savannas, we investigated to what extent the functional effects of fire in a Brazilian savanna occurs via intra- or interspecific trait variability. We sampled 12 traits in communities subjected to three fire regimes in the last 12 years: annual, biennial, and protected. To evaluate fire's relative effects, we fitted a general linear mixed models with species as random and fire as fixed factors, using: (1) all species in the communities (i. e., considering intra- and interspecific variabilities); (2) 18 species common to all fire regimes (i. e., intraspecific variability only); and (3) all species with their overall average trait values (i. e., interspecific variability only). We assessed the relative role of intra- or interspecific variability by comparing the significance of each trait in the three analyses. We also compared the within and between fire variabilities with a variance component analysis. Five traits presented larger intraspecific than interspecific variability, and the main effect of fire occurred at the intraspecific level. These results confirm that it is important to consider intraspecific variability to fully understand fire-prone communities. Moreover, trait variability was larger within than among fire regimes. Thus, fire may act more as an external filter, preventing some of the species from the regional pool from colonizing the cerrado, than as an internal factor structuring the already filtered cerrado communities. © 2012 Springer-Verlag. Source

Pausas J.G.,CIDE CSIC | Ribeiro E.,Fundacion CEAM
Global Ecology and Biogeography

Aim: It has been suggested that on a global scale, fire activity changes along the productivity/aridity gradient following a humped relationship, i.e. the intermediate fire-productivity hypothesis. This relation should be driven by differing relative roles of the main fire drivers (weather and fuel) along the productivity gradient. However, the full intermediate fire-productivity model across all world ecosystems remains to be validated. Location: The entire globe, excluding Antarctica. Methods: To test the intermediate fire-productivity hypothesis, we use the world ecoregions as a spatial unit and, for each ecoregion, we compiled remotely sensed fire activity, climate, biomass and productivity information. The regression coefficient between monthly MODIS fire activity and monthly maximum temperature in each ecoregion was considered an indicator of the sensitivity of fire to high temperatures in the ecoregion. We used linear and generalized additive models to test for the linear and humped relationships. Results: Fire occurs in most 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 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. Main conclusion: 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 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). © 2012 John Wiley & Sons Ltd. Source

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