Spatial patterns in the effects of fire on savanna vegetation three‐dimensional structure

Abstract

Spatial variability in the effects of fire on savanna vegetation structure is seldom considered in ecology, despite the inherent heterogeneity of savanna landscapes. Much has been learned about the effects of fire on vegetation structure from long-term field experiments, but these are often of limited spatial extent and do not encompass different hillslope catena elements. We mapped vegetation three-dimensional (3-D) structure over 21 000 ha in nine savanna landscapes (six on granite, three on basalt), each with contrasting long-term fire histories (higher and lower fire frequency), as defined from a combination of satellite imagery and 67 years of management records. Higher fire frequency areas contained less woody canopy cover than their lower fire frequency counterparts in all landscapes, and woody cover reduction increased linearly with increasing difference in fire frequency (r2 = 0.58, P = 0.004). Vegetation height displayed a more heterogeneous response to difference in fire frequency, with taller canopies present in the higher fire frequency areas of the wetter sites. Vegetation 3-D structural differences between areas of higher and lower fire frequency differed between geological substrates and varied spatially across hillslopes. Fire had the greatest relative impact on vegetation structure on nutrient-rich basalt substrates, and it imparted different structural responses upon vegetation in upland, midslope, and lowland topographic positions. These results highlight the complexity of fire vegetation relationships in savanna systems, and they suggest that underlying landscape heterogeneity needs more explicit incorporation into fire management policies.

Mapping and exploring variation in post‐fire vegetation recovery following mixed severity wildfire using airborne LiDAR

“…This study was used to test two opposing hypotheses about fire severity and vegetation response: (1) high-severity fire causes high biological impact and hence slow recovery (i.e., the public's perception of vegetation response to severe wildfire) or (2) high-severity fire creates the conditions for strong recovery (i.e., fire stimulates germination and recruitment; Ooi et al 2006, Liyanage andOoi 2015). While airborne LiDAR data has been applied to measure many aspects of vegetation structure (especially in forests; Gonzalez-Olabarria et al 2012, Levick et al 2012, Brosofske et al 2014, Harpold et al 2015, its use to map post-fire vegetation recovery across large areas, especially in Australia, is rare (Kane et al 2013(Kane et al , 2014. Moreover, we expected patches of vigorous regrowth to be large (several hectares), reflecting the size of the high-severity patches (85% of the high-severity fire occurred within discrete patches >10 ha in area).…”

Demographic legacies of fire history in an African savanna

“…), so identifying the fire‐free window required to achieve different biodiversity management objectives is challenging. Furthermore, these responses are likely to be species specific, as suggested by a recent landscape‐scale analysis of fire effects on vegetation structure in different vegetation community settings (Levick, Asner & Smit ).…”

Effects of a fast-burning spring fire on the ground-dwelling spider assemblages (Arachnida: Araneae) in a central South African grassland habitat

“…Effects on plants depend on the amount, vertical level and rate at which heat energy is released (Trollope et al 2002), which varies between habitats of different vegetation structure and composition (e.g. Smit et al 2010;Levick et al 2012), influencing other organisms directly.…”