BOZEMAN - As bark beetles continue to devour sickly pine forests, a Montana State University plant physiologist and ecologist wants to better understand how trees are able to defend themselves amidst a warming climate, drought conditions and hungry insects.
Amy Trowbridge, assistant professor in the Department of Land Resources and Environmental Sciences in MSU's College of Agriculture, received a $1 million National Science Foundation grant aimed at investigating the mechanisms of tree death in pinyon pine forests in order to gauge the susceptibility of trees before bark beetle devastation occurs.
The project has direct implications for better understanding the causes related to pine tree death due to severe drought conditions and bark beetle infestations - and for being able to predict which one comes first, Trowbridge said.
"A majority of the research conducted on drought-induced large-scale forest die-off either occurs on the environmental side (climate impacts on tree carbon and water relations) or the entomological side (climate impacts on bark beetles)," Trowbridge said. "There's a big gap in our knowledge when it comes to understanding what's happening with tree chemical defenses and how all three areas interact. We want to understand how the tree as a whole is responding to these threats."
Trowbridge will serve as principal investigator on the three-year grant, along with Henry Adams, assistant professor in the Department of Plant Biology, Ecology and Evolution at Oklahoma State University, William Pockman, professor in the Department of Biology at the University of New Mexico, and Nate McDowell, staff scientist at the Pacific Northwest National Laboratory.
In order to investigate how pinyon pine trees physiologically respond to stressful drought and climate conditions and at what point the bark beetles arrive, Trowbridge and her research team will take "full diagnostics" of a tree's chemistry to understand how trees allocate resources to survive.
"We know the bark beetle prefers stressed or weakened trees and that a healthy tree can generally fight off beetle invasions by using its chemical defenses," Trowbridge said. "But when a tree is already diverting resources to survive in drought conditions, it shifts its chemical defenses for a trade-off to avoid death; it's either going to focus on conserving water, or fight off the beetle, but not both. We want to understand what its priorities are and when those priorities shift."
By creating different levels of drought severity and manipulating water availability in a pinyon forest at the Sevilleta Wildlife Refuge in La Joya, New Mexico, Trowbridge and her team will take "full diagnostics" of a tree's chemistry in part by "lugging large, heavy equipment through forests," according to Trowbridge. The team will measure a tree's photosynthesis, transpiration, starch and sugar concentration, and chemical defenses and will use metrics to determine how, when and where environmentally stressed trees allocate carbon resources.
The goal, according to Trowbridge, is to gauge the "vulnerability threshold" at which a tree becomes more susceptible to the bark beetle.
"Shifts in a tree's chemistry have important implications for the function of the ecosystem overall," Trowbridge said. "If we can use physiological metrics and identify when a tree is no longer able to sufficiently invest in defending itself, we can potentially apply that knowledge to other conifer systems to better understanding bark beetle behavior."
That knowledge is particularly important for species monitoring and the ability to predict large-scale die-off for land managers and to assess the overall health of forests, Trowbridge said. According to the U.S. Forest Service, bark beetles have affected tens of millions of acres of pine forests with demonstrated negative economic and social impacts. In some parts of the country, forest deaths are outpacing the rate of regeneration, according to the USFS.
Trowbridge, who has a doctorate in ecology and evolutionary biology from the University of Colorado, first collaborated with Adams in 2010, who at the time a graduate student at the University of Arizona studying how drought affects trees. Trowbridge was then awarded an NSF post-doctoral research fellowship, which allowed her to work with McDowell and Adams at the Los Alamos National Laboratory investigating trade-offs between tree survival and investment in plant defense chemistry.
Adams said it's fitting he and Trowbridge are collaborating on research again years later, and at a critical juncture in regard to the science of forest health.
"It's really validating to be funded at this level and in a field that we've been investigating for some time together," Adams said. "Trees are dying all across the west, and there (are) all of these scientists studying why. Having Amy take the lead as an expert in tree chemical defenses is really going to help us connect the dots so that we can understand the bark beetle and forest health on a massive landscape scale."
Trowbridge is interested not only in generating new knowledge on the bark beetle frontier but is committed to sharing it was as well, said Tracy Sterling, head of the department of Land Resources and Environmental Sciences.
"Dr. Trowbridge actively seeks out public outreach events to reach audiences of all ages whether it be at the Children's Museum, a middle school, or a local 'Suds & Science' event for adult learners," Sterling said. "Her creative approaches stimulate an interest in STEM and empower students to be curious and confident in what they are learning."
Trowbridge worked with MSU's Academic Technology and Outreach to develop ideas for teaching modules for rural science teachers in Montana, based on her NSF tree mortality study. Trowbridge and Jamie Cornish, outreach specialist with Academic Technology and Outreach, will train teachers on the lesson modules modeled after popular crime science investigator (CSI) programs.
Graduate students involved in the NSF project will also rotate labs between MSU, UNM and OSU, and the students will present a seminar at their hosting university.
Additionally, Trowbridge has reserved grant funds to mentor an undergraduate student from one of Montana's tribal colleges, who will train in MSU labs and support the NSF project.
Trowbridge said she's particularly committed to mentoring and training Native students. She underwent a training hosted by the Pacific Northwest Circle of Success: Mentoring Students in STEM, an alliance funded by the NSF to increase the number of American Indian and Alaska Native students who complete science, technology, engineering and mathematics (STEM) graduate programs. MSU is an allied institution with the program.
"To me, the appreciation and understanding of natural resources and ecosystems imbedded in tribal nations is a no-brainer in terms of how we can parlay that cultural knowledge and expertise into our own research," Trowbridge said. "Many Native students have a knowledge reserve in that field already, which is something I think we need to pay more attention to. That kind (of) interaction is so much about what the land-grant mission is about."