Human-Managed vs. Natural Grazing Systems: Comparing Effects of Relaxing Grazing on Plant Species Composition
For my PhD, I studied the functional similarity of native wildlife and domestic livestock herbivores by comparing plant community shifts following relaxation of grazing across paired livestock-grazed and wildlife-grazed sites in the Serengeti ecosystem of Tanzania. I tested the hypotheses that (1) past grazing has led to very different plant communities, and (2) relaxation of grazing in native and domestic systems will cause plant composition of the two systems to diverge, potentially exhibiting trajectories to different community states. I did this using a grazing exclosure experiment at four pairs of livestock-grazed and wildlife-grazed sites that shared similar environmental and edaphic characteristics. By fencing a series of plots for graduated amounts of time, I was also able to control for and test the effect of plot grazing intensity.
Results showed that while regional differences and site history strongly influence the magnitude of compositional change, overall, relaxing grazing did not lead composition to diverge across management types. Rather, despite significant differences in the magnitude and/or direction of shifts in grass, forb, and sedge relative abundance and differing trajectories of some key species, livestock-grazed and wildlife-grazed plots became more similar in composition across wet seasons. This suggests that differences in impacts across livestock-grazed and wildlife-grazed systems may be due more to aspects of management, including spatial and temporal patterns of grazing, than to inherent functional differences of herbivore type.
This research was done with Mark Ritchie while at Syracuse University.
Results showed that while regional differences and site history strongly influence the magnitude of compositional change, overall, relaxing grazing did not lead composition to diverge across management types. Rather, despite significant differences in the magnitude and/or direction of shifts in grass, forb, and sedge relative abundance and differing trajectories of some key species, livestock-grazed and wildlife-grazed plots became more similar in composition across wet seasons. This suggests that differences in impacts across livestock-grazed and wildlife-grazed systems may be due more to aspects of management, including spatial and temporal patterns of grazing, than to inherent functional differences of herbivore type.
This research was done with Mark Ritchie while at Syracuse University.