Keystone Species Aids Riparian Buffers in Yellowstone

Scientists were puzzled about the sudden regrowth of riparian vegetation in Yellowstone National Park beginning in the 1990s. Only one thing has changed to explain the phenomenon: the reintroduction of wolves to the Park.

Since the 1930s, trees such as cottonwoods, willow, and aspen have been absent from riparian areas in Yellowstone. Park officials believed the elk herds were eating the new growth, but could not solve the problem. However, in the late 1990s the elk stopped congregating near the streams and the trees returned. Researchers at Oregon State University pondered this effect, and ruled out drought, flood, fire, and climate change. The only answer was the reintroduction of wolves to the park, which occurred in 1995. The scientists have determined wolves to be a “keystone species,” which refers to a species whose very presence helps to support the ecosystem of which they are a part and whose extinction would consequently lead to the extinction of other forms of life. Yellowstone sports a population of 250 to 300 wolves today, and their presence has created an unforeseen cascade of biological diversity in the Park. Wolves stalk the elk, so the elk leave the rivers where they are more vulnerable. The riparian trees grow, cooling the water temperatures in the streams, which improves trout populations. Migratory birds return to roost in the new foliage, and beavers come to eat the low-hanging willow foliage. The beavers build dams and create marshland, which brings back the otters, mink, muskrats, and ducks. The elk population has declined slightly since the wolf reintroduction, but this has its benefits as well, since ravens, magpies, golden eagles, bears, bald eagles, and coyotes feed off the elk kills. It may take 20 or 30 years to see the full effects of the wolf reintroduction on the ecosystem as a whole, but Yellowstone is the perfect laboratory – a fully protected 2.2 million acre piece of wilderness.

Washington Post, January 26, 2004