Abstract
Abstract. Fire regimes across the globe have been altered through changes in land use, land management, and climate conditions. Understanding how these modified fire regimes impact vegetation structure and dynamics is essential for informed biodiversity conservation and carbon management in savanna ecosystems. We used a fire experiment at the Territory Wildlife Park (TWP), northern Australia, to investigate the consequences of altered fire regimes for vertical habitat structure and above-ground carbon storage. We mapped vegetation three-dimensional (3-D) structure in high spatial resolution with airborne lidar across 18 replicated 1 ha plots of varying fire frequency and season treatments. We used lidar-derived canopy height and cover metrics to extrapolate field-based measures of woody biomass to the full extent of the experimental site (R2=0.82, RMSE = 7.35 t C ha−1) and analysed differences in above-ground carbon storage and canopy structure among treatments. Woody canopy cover and biomass were highest in the absence of fire (76 % and 39.8 t C ha−1) and lowest in plots burnt late in the dry season on a biennial basis (42 % and 18.2 t C ha−1). Woody canopy vertical profiles differed among all six fire treatments, with the greatest divergence in height classes <5 m. The magnitude of fire effects on vegetation structure varied along the environmental gradient underpinning the experiment, with less reduction in biomass in plots with deeper soils. Our results highlight the large extent to which fire management can shape woody structural patterns in savanna landscapes, even over time frames as short as a decade. The structural profile changes shown here, and the quantification of carbon reduction under late dry season burning, have important implications for habitat conservation, carbon sequestration, and emission reduction initiatives in the region.
Highlights
Fire is an integral component of the functioning of savanna ecosystems, exerting top-down control on woody vegetation structure (Bond and Keeley, 2005; Sankaran et al, 2005)
Three woody canopy structural variables were retained in the step-wise linear regression procedure: mean canopy height (MCH), total canopy cover (Cov1m), and overstorey canopy cover (Cov10m): www.biogeosciences.net/16/1493/2019/
When explanatory variables were considered independently, fire treatment was more influential than block position on variation in woody cover ( Akaike information criterion (AIC) = 70.25 vs. 90.67), but not for mean canopy height ( AIC = 59.96 vs. 48.93) or woody biomass
Summary
Fire is an integral component of the functioning of savanna ecosystems, exerting top-down control on woody vegetation structure (Bond and Keeley, 2005; Sankaran et al, 2005). Savanna fires restrict vegetation vertical growth through a “fire-trap” mechanism, whereby young trees are constrained to low woody re-sprouts under high fire frequencies (Higgins et al, 2000; Freeman et al, 2017). The structural modifications that fires impart on savanna vegetation have been shown to impact both vertebrate (Woinarski et al, 2004) and invertebrate (Andersen et al, 2012) taxa. Fire-driven structural changes to savanna vegetation have important implications for climate regulation, as savanna fires contribute significantly to atmospheric emissions of greenhouse gases through biomass combustion (Hurst et al, 1994; van der Werf et al, 2010).
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