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Woody plant encroachment (WPE) is a global trend that occurs in many biomes, including savannas, and accelerates with fire suppression. Since WPE can result in increased storage of soil organic carbon (SOC), fire management, which may include fire suppression, can improve ecosystem carbon (C) sequestration in savannas.At our study site in Kruger National Park, South Africa, we used a long‐term (~70 year) fire experiment to study the drivers and consequences of changes in woody cover (trees and shrubs) on SOC sequestration. We surveyed four fire manipulation treatments, replicated at eight locations within the park: annual high‐intensity burns, triennial high (dry season) and low‐intensity (wet season) burns, and fire exclusion, to capture the range of fire management scenarios under consideration. The changes in woody cover were calculated over a period similar to the experiment's duration (~80 years) using aerial photographs (1944–2018). Soils were analysed to 30 cm depth for SOC and δ13C, under and away from the tree canopy to isolate local‐ and landscape‐level effects of WPE on SOC.The largest increases in woody cover occurred with fire exclusion. We found that plots with higher increases in woody cover also had higher SOC. However, trees were not the only contributor to SOC gains, sustained high inputs of C4‐derived C (grasses), even under canopies in fire suppression plots, contributed significantly to SOC. We observed little difference in SOC sequestration between cooler triennial (wet season) burns and fire suppression.Synthesis. Grass input to soil organic carbon (SOC) remained high across the full range of woody cover created by varying burning regimes. The total SOC stocks stored from tree input only matched grass‐derived SOC stocks after almost 70 years of fire exclusion. Our results point to C4 grasses as a resilient contributor to SOC under altered fire regimes and further challenge the assumption that increasing tree cover, either through afforestation schemes or fire suppression, will result in large gains in C sequestration in savanna soils, even after 70 years. [ABSTRACT FROM AUTHOR]

Savanna vegetation is controlled by bottom-up (e.g. soil and rainfall) and top-down (e.g. fire and herbivory) factors, all of which have an effect on biodiversity. Little is known about the relative contribution of these factors to biodiversity, particularly the long-term effects of top-down disturbance on patterns of woody plant composition. The aim of this study was to identify if various degrees of disturbance regimes create distinct woody species community assemblages. Data were collected over 1820 plots across Kruger National Park, South Africa. Woody species were identified and categorized into one of three height classes: shrub (0.75-2.5 m), brush (2.5-5.5 m), and tree (>5.5 m). Species richness and composition were calculated for each site and height class. A combination of long-term fire and elephant density data were used to delineate areas with varying degrees of top-down disturbance (i.e. low, medium and high). Using these degrees of disturbance, species composition was identified and community assemblages constructed according to each disturbance regime. Our results suggest that areas with similar disturbance regimes have similar species composition. Shrub composition was mainly responsive to the number of fires between the years 1941-1990, while tree composition was more responsive to elephant disturbance. A few dominant species were found equally under all degrees of disturbance at all height classes, while others were more regularly found under specific disturbance regimes at particular height classes. This study highlights that while species richness does not appear to be influenced by long-term, top-down disturbance regimes, species community composition may be responsive to these disturbances. Most species and structural classes persisted across all disturbance regimes, but the long-term effects of top-down disturbances can influence compositional and structural biodiversity. This information provides context for management policies related to artificial water provision, elephants and fire. [ABSTRACT FROM AUTHOR]