Gray wolves (Canis lupus) were reintroduced into Yellowstone National Park in 1995–1996. In August 2004 we measured plant architecture of Geyer willow (Salix geyeriana) stems along three 100-m reaches of Blacktail Deer Creek in Yellowstone's northern elk (Cervus elaphus) winter range to evaluate changes in patterns of browsing and height growth following wolf reintroduction. Average browsing intensities (n = 3 stream reaches) of 100% in 1997 decreased to 0%–55% by 2003, whereas average stem heights of 25–74 cm in 1997 increased to 149–268 cm by 2003, indicating that willow height growth was inversely related to browsing intensity. In addition, average willow canopy cover over the streams increased from <5% in 1997 to 14%–73% in 2004. These findings were consistent with a hypothesis that increased willow heights following the 1995–1996 wolf reintroduction represent a trophic cascade involving wolves, elk, and deciduous woody vegetation.
Beschta, Robert L. and Ripple, William J.
"Increased willow heights along northern Yellowstone's Blacktail Deer Creek following wolf reintroduction,"
Western North American Naturalist: Vol. 67
, Article 17.
Available at: http://scholarsarchive.byu.edu/wnan/vol67/iss4/17