BACKGROUND

Why was elk browsing on cottonwoods and willows so intense during much of the 20th century?

Ripple and Beschta (2004a) used a combination of qualitative (historical documents, reports and records; historical photographs) and quantitative (population census) data to reconstruct wolf and elk population estimates during the 20th and early 21st centuries for the Greater Yellowstone Ecosystem. For example, National Park Service personnel kept records of the numbers of predators killed in Yellowstone each year after it was established in 1872, and these numbers give us an estimate of wolf population sizes in the Park until the last recorded wolves were eliminated in the mid-1920's. Elk census data were collected beginning in 1929 and continuing into the present, but prior to 1929 the population size was estimated based on partial censuses and visual estimates (thus the shaded portions of the graph). The diagrams in this figure set are a summary of that information, and show the relationship between wolf population sizes and elk population sizes before and after wolves were extirpated, and again after wolves were restored (Ripple and Beschta 2004a).