Long-term monitoring of elephant impact on the woody vegetation in the Tembe Elephant Park, South Africa

Abstract

The African Elephant is a key component of the savanna ecosystem. They contribute to the generation of habitat for smaller vertebrates, as well as invertebrates, by the breaking of branches or uprooting of trees. Elephants also play a role in seed dispersal, germination and sapling recruitment. All these functions are advantageous to the ecosystem if the elephant population size is acceptable for the size of the reserve and the amount of available forage. The Tembe Elephant Park covers an area of 30 013 ha and is situated in northern KwaZulu Natal. This reserve has a diversity of vegetation types and is part of the Maputaland Centre of Plant Endemism and the Maputaland-Pondoland-Albany Hotspot of Biodiversity. Elephant numbers in the park are currently high and the elephant population is still increasing. This is threatening, especially to the endemic Sand Forest communities within the park. The extent of elephant impact in Tembe Elephant Park, South Africa, was investigated and compared to data collected six years prior to the current study. Elephant impact was determined in 44 transects within nine communities across the park. Percentage canopy removal was calculated for the woody individuals found in sites and with this data the targeted size classes and species could be identified. The preferences of elephants for specific woody species were determined by three electivity indices. Elephant utilisation in Tembe Elephant Park, as reflected by percentage canopy removal, increased since 2004 as the elephant population increased. Communities that experienced high values in 2010 of elephant utilisation were the Closed Woodland 1, Mature Sand Forest, Open Woodland 1 and the Closed Woodland 3. Not only did the actual canopy volume removed by elephant increase with approximately 57%, but the total canopy volume available for browsing decreased extensively since 2004. The size classes targeted by the elephants remained approximately the same from 2004 to 2010 although the 2010 results showed that elephant canopy removal percentage increased in the large size classes. This was expected as elephants target individuals with large stem diameters. A change in the selection for woody species by elephants was clear, but the change in species preference made future projections of canopy removal problematic. Elephants seem to utilise a species at extreme levels until the species is almost extirpated, then they move onto the next target species. This routine is evident in the results as highly preferred species in 2004, with high canopy volumes available and removed, had low canopy availability and electivity ratios in 2010, consequently the elephants moved on from these species as individuals became scarce. It was clear that the structure of individuals, populations and communities were being altered, selected species were facing extirpation and composition of communities was changed through the browsing manners of elephants. Management actions should be implemented to prevent irreversible damage to the vegetation and to conserve the woody species currently under threat.