Abstract
AbstractFire resistance traits drive tree species composition in surface‐fire ecosystems, but how they covary at different scales of variation and with the environment is not well documented. We assessed the covariation of bark thickness (BT), tree height, and crown base‐to‐height ratio across Alpine forests, after accounting for the effects of tree diameter and competition for light on individual trait variation. Traits consistently correlated across individuals and communities, although the variance of BT mainly occurred among species, whereas crown elevation traits varied mainly within species. Aridity, temperature, and competition contributed to explain the variation of fire resistance traits among and within species, driving a trade‐off between fire resistance and the ability to compete for light. Thick‐barked species (fire‐tolerant) that self‐prune their lower branches (flame‐avoiders) dominated the most fire‐prone and flammable communities in sub‐Mediterranean southern Alps, whereas thin‐barked tree species that grow tall (competition for light) dominated the least fire‐prone communities in the northern Alps. Our findings suggest a long‐term interaction between mountain tree species and fire regime. Higher allocation to trunk elongation occurs in moist and shade environments, while higher allocation to thicken the bark and distancing the crown base from surface fuels occurs in open‐canopy, dry forests where fire spreads with higher intensity.
Highlights
Fire is a major ecological factor that shapes the composition of plant communities and ecosystem functioning
Our results suggest that (1) fire resistance traits vary across different ecological scales and they correlate in the same direction across individuals and communities; (2) trait covariation mostly results from trait differences among species along gradients of tree cover and aridity, intraspecific variation accounts for a substantial part of trait–environment relationships; and (3) fire resistance and competition for light strategies trade-off in Alpine forests
The resistance to surface fires of the dominant pines Pinus nigra and Pinus sylvestris is well documented in historical studies (Fule et al 2008, Leys et al 2014)
Summary
Fire is a major ecological factor that shapes the composition of plant communities and ecosystem functioning. The study of environmental filtering processes needs to account for the variation of traits with ontogeny (e.g., size) and biotic interactions such as competition (Bennett et al 2016) This variation is important in the study of fire resistance strategies when considering TH which is largely involved in competition for light (Falster and Westoby 2003, Kunstler et al 2016). It has been shown that fire-resistant pine species are tall with thick barks and high self-pruning (Schwilk and Ackerly 2001, Pausas 2015) It is not well documented how variation in fire tolerance (thick bark) and flame avoidance (elevated crown) is distributed across individuals, species, communities, and biogeographic regions, and how this variation correlates with environmental gradients (Pausas 2017)
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