Are Termite Mounds Always Grazing Hotspots? Grazing Variability with Mound Size, Season and Geology in an African Savanna.

Abstract:

Foraging site selection by large herbivores is influenced by multiple factors varying across landscapes and spatial scales. Termite mounds harbour highly nutritious plants compared with the savanna matrix, making them preferred foraging patches in many savannas. However, it is unknown whether termite mounds equally influence herbivore grazing intensity across geological substrates and mound sizes. These knowledge gaps hamper our ability to draw general trans-ecosystem conclusions about the effect of termite mounds for savanna herbivores. We measured grazing intensity on mounds of three different size classes (small, medium and large) across two geologies with differing soil nutrition (granite and basalt) in Gonarezhou National Park, Zimbabwe. We recorded measurements across three seasons (hot wet, cool dry and hot dry), and at multiple distances from mounds. Grazing intensity on mounds was higher on nutrient-poor granite than nutrient-rich basalt, and termite mounds of all sizes had a significant effect on grazing on granite during the cool dry season. Grazing was highest on large mounds on both geologies throughout the year. Large mounds also had the largest spatial influence on grazing in the cool dry season, up to 8 m beyond the mound edge on granite and 2 m on basalt. When scaled up to the landscape level, mounds influenced about 15% of the granite landscape, but only about 0.5% of the basalt landscape. Our results show that the positive effects of mounds on grazing intensity were pronounced on nutrient-poor soils but negligible on nutrient-rich soils, and that the magnitude of these effects varied across seasons and with mound size.