New aspen trees are taking hold in Yellowstone National Park, thanks to wolves reintroduced thirty years ago, and western Colorado could eventually see similar benefits.
A study released last week found that aspen trees in the Wyoming park are now at least 5 centimeters in diameter, a milestone meaning they can now be counted among the canopy’s older trees.
Before wolves were reintroduced in 1995, elk had been eating virtually all young aspen saplings before they could grow. As a result, Yellowstone hadn’t seen new aspens maturing in its forests since the 1940s — around the same time wolves were removed from the landscape.
The study’s lead author, Luke Painter, said there are other factors involved, but wolves have played a key role in ecosystem recovery.
“It's not just the wolves,” Painter said. “There are other things affecting the elk, but it wouldn't happen without the wolves. The wolves are an essential part of this whole thing, and I think they created the sort of tipping point.”
In the 1980s and 90s, large numbers of elk were dying of starvation as they ran out of food in the winter. Painter said wolves added predatory pressure, and combined with bears and cougars, have managed the population and made for a healthier elk herd.
Only about a third of the sites researchers surveyed saw widespread aspen growth, but Painter said that variability is evidence of wolves’ effect on the ecosystem.
“The public story was, ‘Oh, wolves have fixed everything, and it's all recovered.’ Well, no, that's not true. It's more complicated than that,” Painter said. “The fact that it's highly variable on the landscape is itself what we would expect with the trophic cascade, that it wouldn't affect everything just evenly everywhere.”
Yellowstone is often considered a case study of the potential ecosystem benefits of reintroducing wolves, creating a trophic cascade of effects up and down the food chain.
Aspen trees play a critical role in ecosystems across the West — supporting habitat for certain berry bushes, birds and insects.
Painter said aspen trees also increase climate change resiliency, in part by providing food and building materials for beavers.
“With all that increased snow melt, beavers can help hold that water up there so it trickles down through the summer,” Painter said.
As climate change fuels more fires in Colorado, Painter said wolves could also help make sure new aspens can grow in burn scar.
Painter said ecosystem-level changes take time to develop, and Coloradans shouldn’t expect any drastic effects right away.
