Nutrient hotspots for wild grazing ungulates in a miombo ecosystem, western Tanzania

Abstract

While the movement pattern of grazing ungulates is strongly dependent on forage quality whose use of nutrient hotspots has rarely been quantified, especially in miombo ecosystems where soil-nutrient quality is low. Few experiments have been conducted to determine the role of nutrient hotspots derived soils in improving forage quality in miombo ecosystems. Nutrient hotspots strongly attract ungulates in nutrient poor habitats such as savanna systems. However, little is known about their seasonal importance for different grazing ungulate species. No study has quantified the potential re-distribution of nutrients into the surroundings away from hotspots. The current study assessed nutrient hotspot (i.e., grazing lawns and termite mounds) use by ungulates in a highly threatened miombo ecosystem of the Issa valley, western Tanzania. Study used indirect observation, camera traps and stable isotope analyses over a one year period to identify seasonal and spatial variations in habitat use of various wild mammalian grazers around ten termite (Macrotermes sp.) mounds, six grazing lawns and their respective control sites. Grazer visitation rates were nine and three times higher on termite mounds and grazing lawns, respectively compared to control sites. During the rainy season, termite mounds were more frequently used than grazing lawns while grazing lawns were more frequently used during the dry season. A total of 32 camera stations recorded 244 wildlife encounter events in total. Camera data show that ungulates used hotspot areas four times more frequently in comparison to their control plots. Cynodon dactylon grass planted in soils derived from termite mounds had twice as high nitrogen and phosphorous contents compared to grasses planted in grazing lawn soils and control site soils. Stable isotope analysis highlighted that dung deposited by grazers around hotspots originated from grasses within hotspot areas, hence proving that grazers are responsible for modifying nutrient stability around these hotspots. This study results highlight that nutrient hotspots play a significant role in influencing seasonal soil and forage nutrient dynamics, habitat selectivity, and hence grazing activities/ movements of wild ungulate grazers in miombo ecosystems. The study concludes that nutrient hotspots are important for various ungulates in otherwise nutrient – poor miombo systems.