Deciphering fire tolerance of trees at the Amazonia-Cerrado transition by trait-based approach: Implications from species to communities.

Premise: Understanding how fire impacts trees is essential for predicting the effects of novel fire regimes on plant diversity in the transition between the world's two most diverse biomes, the Cerrado and the Amazonia. Here we addressed knowledge gaps regarding physiological damage and mortality in transitional species within fire-prone ecosystems.

Methods: In a manipulative fire experiment, we burned a transitional woodland savanna for six consecutive years after it had been fire-excluded for 33 years. We classified the most abundant tree species according to their fire tolerance and examined the relationship between fire tolerance and key morphological and ecophysiological functional traits. These traits were related to leaf economics spectrum, bark investment, wood density, flammability, and physiological drought tolerance.

Results: Species had three main fire tolerance strategies, reflected in their investment in the outer and inner bark, wood density in branches and the main trunk, changes in leaf water potential, and water and dry matter ratios in leaves. The inner and outer bark and the level of protection of the sprouting buds better explained tree mortality and topkill. Under very frequent fires, fire-sensitive species had the highest mortality rates and fire-thrivers became the most abundant species.

Conclusions: Transitional tree species had different response strategies to fire based on their tolerance, which directly influences their survival and the overall structure of the community. Our findings suggest likely shifts in tree community structure in response to novel fire regimes.