Decadal Fire Effects on the Structure, Composition, Diversity, and Aboveground Carbon Stocks of a Neotropical Savanna

Fire is a common disturbance in the Brazilian savanna (the cerrado), wherein high-frequency fires drive the vegetation structure, composition, function, and dynamics of savanna ecosystems. Under climate change pressure, further understanding of fire-vegetation relationships and interactions can provide new approaches for establishing integrated fire management strategies and can promote post-fire savanna vegetation recovery. To understand how 15 years of annually manipulated burning has affected vertical and horizontal structures of the vegetation, species composition and diversity metrics (species richness, Shannon's diversity, and Pielou's evenness), and aboveground carbon stocks, we surveyed all woody plant species with a diameter greater than three centimeters, in 15 plots of a typical Brazilian savanna (cerrado stricto sensu) at an experimental research station in central Brazil (the cerrado biome). The 15 plots (five plots per treatment) had been differently affected by fire events over a decade, and comprised three treatments: (i) annual fire, (ii) legacy fire (>15 years since the last fire event), and (iii) control (not burned in the past 30 years). A non-metric multidimensional scaling (NMDS) analysis indicated that fire had a significant effect on the species composition among the treatments; some species benefited from fire, such as Erythroxylum suberosum, whereas other species propagated better without fire, such as Roupala montana and Dalbergia miscolobium. Over a decade of annual fire events have led to decreases in Shannon's diversity, species richness, and stem density, which were significantly lower in the annual fire treatment than in the control and legacy fire treatments. Stem density by diameter and height size classes (except for the 1-2 m class and above 8 m class) was higher in the control than that in the annual fire treatment, but the number of dead trees did not differ between the control and the annual fire treatment. Our results also showed that fire was a factor in changes in the evaluated parameters, such as in the annual fire treatment, where fire reduced the amount of biomass, and therefore the carbon stocks. This study suggests that, if burned yearly, typical Brazilian savannas can become less biodiverse in terms of woody plant species which negatively affects their fire resilience. Therefore, fire management practices should focus on determining the frequency of fire disturbances from which these ecosystems may benefit the most.