Elephant browsing impacts in a Zambezian Baikiaea woodland with a high density of pumped waterholes

Abstract

Foraging by African savanna elephant ( Loxodonta africana ) and other herbivores tends to result in a piosphere effect around water sources, with increasing pressure on vegetation as distance to water decreases. This study aimed to investigate the impacts of pumped waterholes on woody vegetation in the southern portion of Zimbabwe’s Zambezi National Park, a Baikiaea woodland ecosystem characterised by high elephant densities. The recent rehabilitation and addition of pumped waterholes has resulted in a dense waterhole network in the park, prompting concerns around potential negative impacts on vegetation. Sampling plots were located at different distances from four pumped waterholes in Baikiaea plurijuga and Terminalia sericea woodlands. Elephant browsing levels and vegetation structure were assessed across three plant height classes (0.2 - < 1 m; 1 - < 3 m and ≥ 3 m). Elephant dung counts were also conducted to provide a relative measure of elephant occupancy. A decline in elephant browsing with distance to waterholes was evident in both woodland types, though browsing was consistently higher in the Terminalia woodland. Structural impacts of elevated elephant browsing around waterholes were limited in the Baikiaea woodland. However, substantial reductions in the basal area and canopy volume of trees were evident closer to waterholes in the Terminalia woodland, with widespread conversion of woodland to shrubland. Elephant dung decreased with distance from waterholes in both woodland types, confirming that elephant occupancy was higher closer to waterholes. Overall, clear effects of pumped waterholes were evident. The ecological integrity of the Terminalia woodland in particular appears to be under threat, especially as the current surface water regime places most of it within 3 km of waterholes. The cessation of pumping at some waterholes was thus recommended, to achieve a more heterogenous browsing regime in the area.