Elk Study Shows That Some Grazing Benefits Rangelands
Herds of big game animals such as elk can actually increase the productivity and diversity of the plants in their habitat when the density of those populations is low, a College of Agriculture, Biotechnology and Natural Resources assistant professor has revealed in a recent study.
Assistant Professor Kelley Stewart conducted her work at the Starkey Experimental Forest and Range in northeastern Oregon, studying how different sizes of elk populations affected their habitats and food availability. Stewart and her team also studied the body condition and pregnancy rates of the elk.
Stewart's study compared two elk populations - a low density population of 10 elk per square mile and high-density herd of 60 elk per square mile located in similar habitats. Each habitat included exclosures in which the herds could not graze.
Stewart's research showed that not only were the smaller herds healthier, with better body condition, pregnancy and recruitment of calves into the population, but their habitats actually benefited from the animals' grazing. Areas foraged by low-density elk herds had greater plant growth than areas where no forage by elk occurred at all. Plants were stimulated to grow and plant communities became more diverse than in areas where no foraging occurred. Forbs and shrubs benefited as well as grasses.
Dr. Kelley Stewart an assistant professor at CABNR, found that low density elk herds were healthier, produced more calves and were actually better for the environment than land that had no grazing at all.
Stewart said this phenomenon, called "herbivore optimization," is similar to mowing your lawn. If you don't mow your lawn, the grass grows, forms seedheads and then dies back. But if you mow every week or two, the plants continue growing vegetative parts.
"But if we mow too often, the lawn can't grow fast enough and we lose biomass - similar to what we see in areas that are overgrazed," Stewart said.
Stewart believes these findings - that properly managed elk populations can promote biodiversity and ecosystem functioning - would apply to other large foraging animals, including deer and antelope.
Stewart, who is starting her fourth year at CABNR, is also researching mule deer migration and overwinter survival. She is studying deer herds in the Ruby Mountains, the Tahoe Basin and Lander County to determine herds' pathways, migration strategies and energy expenditures during migration. She also is doing a large study on mountain lions in which she and a Ph.D student are looking at source-sink dynamics and prey selections of lions in the Tahoe Basin.