“Gray wolves had disappeared from Yellowstone National Park by 1930 following extensive habitat loss, human hunting and government eradication programs. Without these top predators, populations of elk grew unfettered. At their peak population, an estimated 18,000 elk ranged across the park, chomping on grasses and shrubs as well as the leaves, twigs and bark of trees like quaking aspen. This stopped saplings from establishing themselves, and surveys in the 1990s found no aspen saplings…
When wolves were reintroduced in 1995, the picture began to change. As wolf numbers rose, the elk population in the park dropped sharply, and it is now down to about 2,000.
In the new study, published Tuesday (July 22) in the journal Forest Ecology and Management, Painter and his colleagues surveyed aspen stands — specific areas of the forest where these trees grow.
The team returned to three areas surveyed in 2012 to examine changes to aspen sapling numbers. Of the 87 aspen stands studied, a third had a large number of tall aspen saplings throughout, indicating the trees are healthy and growing. Another third of the stands had patches of tall saplings.”
From Live Science.