Bark protection and light-adapted photosynthesis influence woody productivity of Cerrado trees in changing fire regimes.

Abstract

Background and aims: Changing fire regimes within open ecosystems can have important impacts on plant vulnerability, carbon cycling and ecosystem functioning. Thus, in this study, we investigate stem net primary productivity (NPP) dynamics of savanna vegetation in the Amazon-Cerrado transition, making use of an experimental fire and ecosystem monitoring project. We aimed to determine i) how different species contribute to plot-level stem NPP and how this changes with fire frequency; ii) how different fire frequencies affect the average stem NPP and survival of dominant species; and iii) if fire-induced changes in species-level stem NPP and survival are influenced by functional traits.

Methods: We use tree inventory data (height and diameter of stems) to quantify plot- and tree-level stem NPP across unburnt, annual, biennial and triennial fire frequencies. We compare before and after estimates of average stem NPP and survival of dominant species using mixed-effects models, and identify key traits linked with changes in productivity and survival via principal component and regime-interval-trait interaction analyses.

Key results: Generalist species dominate stem NPP in unburnt conditions (Tachigali vulgaris accounts for 72% of NPP), but become less dominant within our less frequent fire regimes (biennially and triennially burnt plots), which favour more sclerophyllous savanna trees. There is a trade-off between plant productivity and tolerance to fire, influenced by functional traits. In less frequent fire conditions (triennially burnt plots), tree growth and productivity are maintained by bark protection, high photosynthetic rates and photosynthetic shade intolerance.

Conclusions: These findings allow us to better predict how fire regimes of varying frequencies will filter the communities of Cerrado trees, and which set of species will confer greater resilience to landscapes across this threatened region. The diverse productivity strategies of Cerrado vegetation are determined by the interaction between fire regimes and functional traits. Burning can successfully limit woody encroachment and help conserve open ecosystem diversity and functioning in the Cerrado.