Contrasting effects of cattle and wildlife on the vegetation development of a savanna landscape mosaic
Journal of Ecology
1. Through their effects on plant communities, herbivores can exert strong direct and indirect effects on savanna ecosystems and have the potential to create and maintain savanna landscape heterogeneity. Throughout much of sub-Saharan Africa, periodic creation and abandonment of livestock corrals leads to landscape mosaics of long-term ecosystem hotspots that attract both cattle and large ungulate wildlife.
2. The development and maintenance of vegetation in these types of hotspots may be controlled in part by herbivory. Cattle and wildlife may have different, potentially contrasting effects on plant succession and plant–plant interactions. We ask how cattle and wild herbivores affect the maintenance and vegetation development of corral-derived landscape heterogeneity (0.25–1.0 ha treeless ‘glades’) in Laikipia, Kenya, through their effects on long-term successional and short-term plant–plant dynamics.
3. We used the Kenya Long-term Exclosure Experiment to exclude from glades different combinations of cattle, large ungulate wildlife (i.e. zebras, gazelles and other antelopes), and mega-herbivore wildlife (i.e. giraffes and elephants). We first assessed long-term changes in cover of the dominant grass species, Cynodon plectostachyus and Pennisetum stramineum (the early- and late-dominant species, respectively). We then used a neighbour removal experiment to test the effects of different herbivores on competition and facilitation between the two glade grass species.
4. In the long-term experiment, we found that large ungulate wildlife reinforced landscape heterogeneity over time by helping maintain glades in their early C. plectostachyus-dominated form. Cattle and mega-herbivore wildlife, on the other hand, appeared to reduce the positive effects through forage preference for C. plectostachyus.
5. In the neighbour removal experiment, we found that each grass species benefited from facilitation when it was the preferred forage for the dominant grazer. Facilitation of C. plectostachyus by P. stramineum was strongest when cattle co-occurred with wildlife, whereas facilitation of P. stramineum by C. plectostachyus was strongest when cattle were absent.
6. Synthesis. Our results demonstrate that different combinations of cattle and wildlife have different effects, largely via contrasting forage preferences, on the persistence of landscape heterogeneity in this savanna landscape. More generally, we provide evidence for contrasting effects of cattle and wildlife on short-term plant interactions (facilitation) and successional processes within the herbaceous plant community.
Veblen, K.E. and T.P. Young. 2010. Contrasting effects of cattle and wildlife on the vegetation development of a savanna landscape mosaic. Journal of Ecology 98: 993-1001.