Fire regimes are changing over much of the world with uncertain consequences for carbon storage and biodiversity. Anticipating the impact of these global changes requires an understanding of how plant communities are adapted to fire, which can be used to inform global models that rely on plant functional traits to predict changes in the carbon cycle. To asses the adaptability of plants to changing fire regimes, we analyze a key fire tolerance trait, relative bark thickness, across 572 woody plant species to determine the broad biogeographic patterns in bark thickness, the driving mechanisms behind trait variability, and draw inferences about how communities may respond to shifting fire regimes.
We demonstrate that species investment in bark converges predictably according to fire regime and precipitation seasonality across multiple long-diverged clades distributed across the globe. Local environmental conditions characterizing a species’ distribution explained 50% of the variance in bark thickness among species, and bark thickness is less constrained across the plant phylogeny than would be expected under Brownian evolution, suggesting evolutionary lability. Variability of bark thickness within and across biomes reveals diverse patterns of estimated vulnerability to future climates and increased exposure to fire. We find that large amounts of moist tropical rainforest and northern temperate forests are especially vulnerable whereas seasonal tropical transitional forests and savannas are more robust.