A new study led by a team of University of Colorado scientists shows that mid-level altitude forests are the most sensitive to rising global temperatures and a decline in snowpack
The study published September 9th in the journal Nature Geoscienceswas done in California but researchers say its findings have implications across the entire West.
Using satellite images and ground measurements, scientists looked at so-called mid level forests from about 6,500 to 8,000 feet in the Sierra Nevada. It’s where much of that region’s water supply originates originates and where many live and recreate. The bulk of the Sierra Nevada Mountains' annual precipitation comes from snow.
Researchers found that a forest's ability to “green up” there in the summer months depends heavily on whether there’s been a healthy snow pack the previous winter.
As the earth warms, and precipitation increasingly comes as rain rather than snow, scientists say forests at these altitudes will become even more stressed, and vulnerable for insect outbreaks and wildfires.
Noah Molotch of the Institute for Arctic and Alpine Research at CU-Boulder co-authored the study along with Ernesto Trujillo, also with the university.
"In general, we’re going to have less water storage in the form of snow pack in the future," Molotch says. "And our study shows that the forests are quite sensitive to this."
Molotch says one important focus of the study was on the “tipping point,” or the line between mid-level forests that are sustained by precipitation and snowmelt and those at higher elevations sustained by sunlight and temperature. It's rising, which could have serious implications for water managers and users, as well as the health of the forest.
"As the region warms, we would hypothesize that that elevation would continue to move up the mountain," Molotch said. "And as it does, runoff production from these higher elevations will continue to go down."
