Abstract
Fire regulates the structure and function of savanna ecosystems, yet we lack understanding of how cyclic fire affects savanna carbon dynamics. Furthermore, it is largely unknown how predicted changes in climate may impact the interaction between fire and carbon cycling in these ecosystems. This study utilizes a novel combination of prescribed fire, eddy covariance (EC) and statistical techniques to investigate carbon dynamics in frequently burned longleaf pine savannas along a gradient of soil moisture availability (mesic, intermediate and xeric). This research approach allowed us to investigate the complex interactions between carbon exchange and cyclic fire along the ecological amplitude of longleaf pine. Over three years of EC measurement of net ecosystem exchange (NEE) show that the mesic site was a net carbon sink (NEE = −2.48 tonnes C ha−1), while intermediate and xeric sites were net carbon sources (NEE = 1.57 and 1.46 tonnes C ha−1, respectively), but when carbon losses due to fuel consumption were taken into account, all three sites were carbon sources (10.78, 7.95 and 9.69 tonnes C ha−1 at the mesic, intermediate and xeric sites, respectively). Nonetheless, rates of NEE returned to pre-fire levels 1–2 months following fire. Consumption of leaf area by prescribed fire was associated with reduction in NEE post-fire, and the system quickly recovered its carbon uptake capacity 30–60 days post fire. While losses due to fire affected carbon balances on short time scales (instantaneous to a few months), drought conditions over the final two years of the study were a more important driver of net carbon loss on yearly to multi-year time scales. However, longer-term observations over greater environmental variability and additional fire cycles would help to more precisely examine interactions between fire and climate and make future predictions about carbon dynamics in these systems.
Highlights
Savannas are both ecologically and economically critical ecosystems at regional and global scales
To elucidate how ET and water use efficiency (WUE) efficiency are affected by stomatal dynamics, we modeled the effects of vapor pressure deficit (VPD) on ET
Environmental Conditions Volumetric water content (VWC) of the soils varied among sites as targeted by the study design; rainfall, temperature, and relative humidity were similar among sites as they were separated by less than 10 km (Figure 1)
Summary
Savannas are both ecologically and economically critical ecosystems at regional and global scales. Savannas cover nearly 1/3 of the earth’s land surface [1] and account for approximately 30% of the world’s primary productivity [2] These ecosystems are important sources of food [2] and fiber [3], and they are under increasing anthropogenic pressure that threatens their sustainability [1,2,4]. In addition to the economic benefits they provide, some savanna biomes, such as longleaf pine ecosystems are ecologically important as global ‘‘hot spots’’ for biodiversity [5,6,7]. These ecosystems play an important role in the global carbon cycle, accounting for approximately 30% of the world’s terrestrial primary productivity [2]. It is ecologically and economically important to sustain savanna ecosystems [8]
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