Tropical savannas are ecosystems strongly influenced by seasonality and disturbance such as fire. The Brazilian Cerrado, the richest savanna in plant species worldwide, contains a rich herbaceous-shrub layer that concurrently experience strong intra-annual variability in precipitation and consumption by fire every 2-5 years. To determine how seasonality and fire interact to influence ecosystem dynamics of CO2 and H2O exchange, we established experimental burning plots in open savannas areas (30 × 30 m, 3 treatments= ‘unmanipulated control’, ‘annual burning’, ‘biennual burning, n=4) and burned mid-dry season (July, 2013 and 2015). Additionally, we burned annually plots in the mid-dry season. Within each plot, we randomly established 10 subplots (1×1m2) for ecosystem structure (vegetation) and function (next exchange of CO2 and H2O vapor) sampling. We carried out the sampling during the dry and rainy seasons in 2015 and 2016. Specifically, we asked: (1) How does seasonality and fire act independent and interdependently to impact net ecosystem CO2 and H2O exchange in a Cerrado ecosystem?; (2) How does seasonality and fire act independent and interdependently to impact ecosystem water use efficiency (eWUE) in a Cerrado ecosystem?
Results/Conclusions
Our results show that seasonality (wet vs. dry season) and disturbance (fire) act independently and interdependently to influence the functioning of a Cerrado ecosystem. During ‘wet’ seasons, net ecosystem CO2 and H2O exchange were 2.5 × and 4 × greater than in ‘dry’ seasons; similarly, eWUE was 2 × greater in ‘wet’ than ‘dry’ seasons. Fire treatments also influenced the functioning of a Cerrado ecosystem, but the direction and magnitude of disturbance effects were mixed. While ‘annual burning’ reduced net ecosystem CO2 exchange relative to ‘control’ by 2.5 ×, ecosystem H2O exchange and eWUE were promoted by 1.5- and 2-fold in ‘annual burning’ relative to ‘control’ and ‘biennual burning’ treatments. Finally, seasonality and fire interacted to shape eWUE. For instance, eWUE was greatest in control plots during ‘dry’ than ‘wet’ seasons by 3×. Taken together, our findings show that both seasonality and fire play an important role in mediating ecosystem function in a tropical savanna ecosystem. Further, fire management will likely influence CO2 and H2O exchange differently intra-annually and therefore ecosystem seasonality needs to be taken into consideration within the context of management approaches.