Researchers at Oregon State University's Aspen Project are exploring the possibility that killing off the wolves in northern Yellowstone National Park may be a principal cause for the aspen declines in that area. Ripple and Eric Larsen of the university's Department of Geosciences have been studying photographs, historical records and tree-ring analyses of that region dating back to the mid 1700s. The photos show that the aspen went into a decline in the 1920s and never recovered. That coincides with an effort to eliminate predatory animals in the early 1900s in the country's first national park. It was immediately after the killings, the decline of the aspen was first noted.
Wolves have an affinity for the taste of elk, and fewer wolves meant more elk.
And elk love the taste of aspen. But more importantly, Ripple speculates, the absence of the wolf meant the elk could dine without fear. It may also have changed the elks' foraging habits because they no longer had to remain in clearings where they could see approaching wolves. They were free to dine in the heart of the grove. Their numbers have multiplied greatly.