MISSOULA — A squirrel’s appetite for certain pine seeds may be driving evolutionary changes in lodgepole forests across the West and altering how the trees respond to fire, a study conducted inside Yellowstone National Park has found.
Researchers at the University of Wyoming published their findings last week in the Proceedings of the National Academy of Sciences, where they described the ecological changes facing Western forests as fires become more frequent under a warming climate.
“The squirrels are really good at finding and eating massive numbers of these serotinous cones,” said UW doctoral graduate Matt Talluto, one of the paper’s authors. “If they’re eating from trees that make these closed (serotinous) cones, we’d expect to see trees that make open cones increase in frequency, and that’s what we found.”
Craig Benkman, a professor in UW’s Department of Zoology and Physiology and the paper’s other author, said researchers have long known that lodgepole pines respond to fire by diversifying their cone production.
Trees that grow in areas prone to fire produce closed cones, allowing them to retain their seeds for years, or until they’re released by heat. Given that specialized trait, the trees have adapted to quickly recolonize burned areas across the West.
That was the case following the 1988 Yellowstone fires, where the team conducted its research. Yet the uneven nature of lodgepole recovery after the fires proved perplexing, leading researchers to suggest that squirrels may be playing a role.
The paper argues that red squirrels – common in lodgepole stands – are taking advantage of the dense production of closed pine cones. By eating the closed cones and leaving the open cones, they’re effectively countering the evolutionary impacts of fire, the team suggests.
“When organisms like red squirrels interact strongly with dominant community members, such as lodgepole pine, evolution can be rapid and affect the ecology of the whole community,” Benkman said. “In this case, we have a widespread system where this is very likely occurring.”
As seeds from the fire-adapted trees are consumed by squirrels, the theory goes, trees not adapted to fire proliferate. That, Talluto said, could change the face of the landscape as fires become larger and more intense.
“We have two controlling inputs, fire and squirrels, and if we change one of the inputs, we’re going to change the balancing point of the whole system,” he said. “It might balance out, or it might go the other way, where, eventually, we don’t see forests, we see sagebrush. When you have complex dynamics at play, it’s difficult to predict how that will happen.”
The findings add to a growing scientific consensus that suggests evolutionary changes can happen quickly. It also suggests such changes can have dramatic effects on entire ecosystems.
Besides the red squirrel, Talluto said, no other factors have been identified to explain the patchwork regeneration of lodgepole pines producing open and closed cones.
“A big part of this is really being influenced by a squirrel that weighs a couple of ounces,” said Talluto. “That’s a big biological story. We think of evolution as being a slow process, but it can happen pretty quickly in the system.”