Climate change is fueling the biggest outbreak ever of tree-killing bark beetles. The insects are decimating conifer forests from Alaska to Arizona—and raising concerns that they could reach the Upper Midwest.
By Bob Mitchell BS'76
Another big worry following a major tree kill, either from beetles or fire, is the potential for losing nutrients—especially nitrates—from the system.
“It can be a problem if nitrates get into streams and ground water,” Turner says. “It happens in a lot of the eastern forests. But what we are finding in Yellowstone is that the forests seem to have pretty effective mechanisms for conserving their nitrogen. We are not finding evidence that they ‘leak’ when they are disturbed.”
Research by Jake Griffin, another of Turner’s students, suggests that the trees that survive the beetle attack, along with other vegetation, are quick to take up the nitrogen. But that might change if forest managers opt to bring in loggers to remove the beetle-killed trees.
“Will the amount of nitrate lost from the system increase if you come in with heavy equipment and cut out the remaining trees, along with [performing] the other operations that disturb the soils?” Turner asks. Griffin’s research will help answer this question.
The impacts of the mountain pine beetle do not stop at the edge of the forest. The insects are changing the face of the landscape across the West and beyond—and that’s the scale at which Phil Townsend wants to look at them. For this he needs a tool that lets him step back to get the widest view possible. He’s studying the beetle infestations from space.
“Our work is not tree-based or stand-based. We’re looking over a much larger area. We’re studying how an insect outbreak affects forest characteristics—forest composition, water quality, carbon sequestration,” Townsend explains. “We use satellite remote sensing to develop models of mountain pine beetle infestations.”
One advantage of satellite data is that it has been collected since the 1970s, long before the current beetle outbreak. This lets Townsend’s team track the beetles back through time.
“We can go back to 40 years’ worth of data to look at patterns of how the damage spreads,” he explains. “For instance, we’ve learned that mountain pine beetle infestation usually starts at mid-slope. It quickly fills in the valleys and then moves upslope. It’s like a front marching up the mountainside. This reflects the mountain pine beetles’ mass attack strategy. They storm the trees.”
Before Townsend can make sense of what he sees from space, he has to know what’s happening on the ground. So he starts in the woods, marking off a plot, counting the trees and noting their stage of attack. Later he plugs that data into a computer model that compares the area’s damage to its infrared signature. By analyzing data from dozens of plots across Greater Yellowstone, Townsend has assembled a library of signatures for different types and levels of disturbance.
“We’re not just trying to map whether a stand is dead or has been attacked,” he says. “We’re trying to map the actual percentage of the forest that is damaged, because ultimately we convert this into carbon, nitrogen—all sorts of different things. We’re trying to quantify the effects of this outbreak on the dynamics of the whole system.”
Collecting data in the woods poses some interesting logistics. Beetle outbreaks often occur in remote places, accessible only by foot or horseback. Getting there can be fun, but it takes a lot of time, so Townsend has worked up a shortcut. Using cameras and a spotting scope, he can measure damage on a remote hillside from the side of a road.
But while hiking into the woods takes time and effort, it yields more than raw data. Getting nose to bark with a lodgepole pine can offer a perspective that you can’t get from a satellite. The day after his trip up Signal Mountain, walking through a different forest a few miles to the east, Townsend stops and points to a wad of pitch on yet another big lodgepole pine.
“This tree was successful,” he says. “You can see where the beetle bored in and the pitch came out, and it actually knocked the beetle out. Here’s the beetle stuck in the pitch. This tree defended itself. It may be one of the few trees that actually does succeed.”
“Sometimes the tree does win,” he adds with a smile. “That’s neat to see.”