« A Dangerous Backcountry Hike | Main | Fine art giclee renderings of the “Buffalo vs. Grizzly” incident. »
Trophic Cascade: Pictures of Beaver Sign on Soda Butte Creek
By Mike Tercek | July 30, 2007
For many years, scientists believed that Yellowstone’s northern range (the grazing land north of the central plateau) was overgrazed. This was due primarily to the fact that riparian (stream-side) willows, aspen and cottonwoods had been in decline since the 1920s, when wolves were extirpated from the park. In some areas these plants completely disappeared, while in others they shrank from 6 or more feet tall to less than waist high. However, in the mid-1990s, when the wolves were reintroduced, riparian plants started getting taller again. In some places they are now more than 4 meters (12 ft) tall. Some scientists still think that the northern range is overgrazed –see for example the book “Yellowstone’s Destabilized Ecosystem” by Fred Wagner –but most now agree that the plant community is recovering.
One explanation for this change in riparian plant height involves a “trophic cascade,” which basically means that the wolves scare elk out of certain areas and keep them from mowing down the willows. A “trophic level” is a level in the food chain or food pyramid. Examples of trophic levels are plants, herbivores (grazers), and predators. A “trophic cascade” refers to the fact that changes in one trophic level (the introduction of wolves, which are predators) has effects that trickle (or cascade) down into lower trophic levels. In this case, the effects went from the wolves, to the elk, and then to the plants. This trophic cascade theory is championed primarily by researchers at Oregon State University (see an article by clicking here), but a recent study from the University of Wyoming has cast doubt on it (see this article, click here). See also my web page on the topic here, click here, and my comment on this theory in another blog post, click here.
The debate over the trophic cascade theory will continue for years, but one thing seems fairly certain. Beaver are more active now that they have taller willows to eat. In one of my study sites on Soda Butte Creek, beaver have removed an entire thicket of 12 ft. tall willows in an area approximately 20 ft. x 10 ft.
Here are some pictures:
The Beaver Lodge:
Entrance to the lodge, with the tunnel leading to the creek:
Beaver tracks along the chute where logs are carried to the lodge:
Closeup of the tracks:
The stump left from what was once a 12 ft. willow bush. The stems were about 5cm (2 inches) in diameter:
Topics: General, Mike Tercek, Nature Notes |
Comments
You must be logged in to post a comment.