The lanky and the corky: fire‐escape strategies in savanna woody species

Abstract

Summary1. 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). 2. 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). 3. 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. 4. 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 heightbark-diameter scheme is a powerful framework for understanding the ecology of many savannas.

Post-fire resprouting strategies of woody vegetation in the Brazilian savanna

“…By contrast, the findings of our study indicated that bark thickness and stem diameter were the principal predictors of the type of resprouting, and that the inclusion of tree height in the analysis did not increase its predictive power. Similar findings have been obtained in comparative studies of the fire survival strategies of the vegetation of African and South American savannas (Dantas & Pausas 2013;Pausas 2014). Lawes & Clarke (2011) for example, showed that tree survival was correlated exclusively with bark thickness, rather than stem height or diameter.…”

“…Bark thickness was the most important factor, as observed in previous studies, which indicate that savanna vegetation impacted frequently by fires tends to select species with thicker bark (Dantas & Pausas 2013). The thickness of the bark determines its capacity for thermal insulation, which protects vital stem tissues from flames and high temperatures (Hoffmann & Solbrig 2003;Miranda & Sato 2005;Pausas 2014).…”

“…As a selective pressure, fi re favors the evolution of species with morphological adaptations that confer resistance to fi re and/or the ability to recover (resilience), which ensure that individuals are more likely to survive (Hoff mann et al 2009;Keeley et al 2011;Dantas & Pausas 2013). Th ese adaptations include a thick and corticated rhytidome, which provides the vascular cambium with greater thermal protection (Miranda et al 2002;Dantas & Pausas 2013;Pausas 2014), and protects the meristematic tissues that enable the plant to resprouts in response to a fi re event (Clarke et al 2013;Charles-Dominique et al 2015).…”

“…As a selective pressure, fi re favors the evolution of species with morphological adaptations that confer resistance to fi re and/or the ability to recover (resilience), which ensure that individuals are more likely to survive (Hoff mann et al 2009;Keeley et al 2011;Dantas & Pausas 2013). Th ese adaptations include a thick and corticated rhytidome, which provides the vascular cambium with greater thermal protection (Miranda et al 2002;Dantas & Pausas 2013;Pausas 2014), and protects the meristematic tissues that enable the plant to resprouts in response to a fi re event (Clarke et al 2013;Charles-Dominique et al 2015). Other adaptations include a greater investment in root biomass (Hoff mann & Franco 2003;Oliveira et al 2005;Charles-Dominique et al 2015) and an increased capacity for the underground storage of carbohydrates (Miranda et al 2002;Hoff mann et al 2004;Clarke et al 2013), which provide the energetic resources for post-fi re recovery (Clarke et al 2013).…”

How does resprouting response differ among three species of savanna trees and in relation to plant size?

“…Fire has been occurring in the Brazilian savannas (Cerrado) for 10 million years (Simon et al 2009;Simon & Pennington 2012) and many Cerrado trees have survived fi res because of traits such as thicker bark (Dantas & Pausas 2013) which protects stems from high fi re temperatures and prevent topkill, or deciduous leaves that are less vulnerable to fi re or herbivory damage (Lucena et al 2015). Among Cerrado woody plants, the main consequences of burning are partial to complete loss of aerial biomass and, in more severe cases, plant death (Coutinho 1982;Hoff mann 1998;Hoff mann & Solbrig 2003;Hayashi & Appezzato-da-Glória 2007;Hoff mann et al 2009).…”