Effects of herbivory, fire, and vegetation type on soil compaction and aggregate stability in a semi-arid savanna

Vegetation type is an important component of savannas contributing to changes in soil health. In savanna landscapes, the tree-grass balance is primarily governed by water, nutrients, fire, herbivory, and their interactions. Here we investigated the long-term effect of herbivores, fire, and vegetation type, and their interactions on selected physical properties (bulk density, penetration resistance, aggregate size fractions, and mean weight diameter (MWD)) of water stable aggregates within the crest and foot-slope of 20-year-old Nkuhlu exclosures located in Kruger National Park, South Africa. Burning, herbivory, and open grassland zones had a significant main and interactive ecological impact on all the soil physical properties under investigation. The interactions between fire, herbivores, and vegetation type within the crest and foot-slope of the Nkuhlu exclosure had a significant impact on soil bulk density, with areas under tree canopies having lower bulk density than open grassland zones in all the exclosures. In all the sampling sites, both burnt and unburnt plots of the full exclosure had lower penetration resistance than the control site and partial exclosure. Moreover, unburnt plots and canopy cover increased aggregate size distribution and mean weight diameter of water stable aggregates. Since fire and herbivory are closely linked and bring about changes in soil physical properties, the understanding of the dynamics of fire, herbivory, vegetation, and their interactions can then be used to help make effective management decisions that incorporate concerns of biodiversity in savanna ecosystems.