Kristen Waring walked among thousands of tiny seedlings at Northern Arizona University’s greenhouse complex Monday. In all, she's tracking more than 8,000 southwestern white pine trees, a species found in forests across New Mexico, southern Colorado, Arizona and Mexico. Over the next several years, Waring will plant a total of 30,000 of these pine seedlings.
It’s part of a research project that just received a $4.1 million grant from the National Science Foundation, the largest the university's forestry department has ever been awarded. Waring is leading the multi-layered endeavor to study how the trees adapt to and will be affected by the dual threats of climate change and the white pine blister rust disease.
The deadly fungus has already caused severe damage to southwestern white pines in southern New Mexico and is moving westward into Arizona. It’s expected to affect white pines throughout most of the Southwest in the coming decades and completely wipe out the trees in some areas.
One goal of the NSF-funded research is to figure out ways to best sustain the species into the future, which for Waring is a task humans are obligated to attempt.
“I strongly believe that if we’re causing these problems then we have a responsibility to try to fix them, and both climate change and white pine blister rust fall into that category,” Waring said.
Threatened by an invader
Southwestern white pines grow beside Douglas firs, ponderosa pines and aspen in mixed conifer forests around Arizona's White Mountains and the San Francisco Peaks. The trees have little resistance to the white pine blister rust, a disease native to Asia that hitchhiked to the United States in the early 1900s on infected seedlings. The fungus spreads thanks to airborne spores that get carried by the wind.
The disease, which affects all nine species of white pine in the United States, does its damage by girdling the tree, cutting off the flow of nutrients and water through the plant. It works slowly, taking years or even decades to strangle the tree to death. It attacks both older trees and young ones, leaving little hope that a stand will regenerate once the disease has passed through.
The disease has wiped out 90 percent of the overstory in some white bark pine and western white pine stands, Waring said.
The NSF-funded project involves three other universities and two other Forest Service agencies. It will encompass everything from mapping the genetic makeup of individual trees to flying unmanned aerial vehicles, or drones, over the Southwest's forests to map out where southwestern white pines are distributed across the landscape.
NAU will receive $2.8 million of the grant money. Waring's experiments involve transferring the thousands of southwestern white pine seedlings from greenhouses to raised beds located at different elevations on the North Rim of the Grand Canyon. Then Waring and others will measure the trees' growth as well as other traits like drought tolerance and cold hardiness.
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At the same time, researchers at Oregon State University will grow seedlings collected from the same mother trees as Waring's crop, infect them with the white pine blister rust and then monitor whether the trees die or demonstrate resistance toward the disease.
The teams will then compare data to see how or if disease resistance, drought tolerance and cold hardiness overlap or don’t. Do trees that survive the disease also exhibit an ability to adapt to drought? Or is there a tradeoff — does disease resistance mean a tree isn’t as drought tolerant?
The parallel experiments recognize that the threats of climate change and the fungus exist together. As forest managers are figuring out how to perpetuate the pine species, they must think about trees’ ability to both resist disease and adapt to climate change, Waring said.
Managing for survival
Arizona is in some sense lucky so far. The white pine blister rust hasn’t spread across the southwestern white pine trees’ entire range yet.
“We’re ahead of it,” Waring said. That means the teams’ research can potentially provide ways for forest managers to address the problem proactively.
Planting trees that have disease resistance is a main management strategy for ensuring their survival, Waring said. But if data shows fungus-proof trees aren’t as drought tolerant, then forest managers might want to prioritize planting them in places where they won’t be as affected by warming temperatures related to climate change, Waring said.
Using the same logic, the Forest Service might choose not to thin or replant trees in areas where climate change models say conditions will become inhospitable to them in a few decades.
And if forest managers can map where disease-resistant trees are located in the forests, there’s more leverage to conserve and collect seeds from those trees, she said.
The project looks at the southwestern white pine from a genetic, epigenetic and environmental standpoint, said Amy Whipple, another NAU researcher on the project who is testing how warmer conditions could affect the timing of when certain genes in the trees’ DNA are switched on and off.
“We’re looking at (these) sources of variation to predict what will happen if we do nothing and to predict how we might be able to help (the trees) survive,” Whipple said.