From the Boulder Daily Camera (Laura Snider):
The researchers compared the amount of snow that piled up on the ground under live trees to the snow depth under two kinds of dead trees: those that still had red pine needles on their branches and those that had lost all their needles. The tree stands, which were located in the same valley near Grand Lake, had comparable elevations, slopes and aspects.
The scientists found that the snow accumulation under the dead, needle-less trees was 15 percent more than the snow under both live trees and dead trees in the “red phase,” when the needles are still attached.
Evan Pugh, a CU doctoral student who led the study, said trees with needles — red or green — are able to intercept the snow before it hits the ground. The snow that sticks to the needles is often returned to the atmosphere as water vapor via the process of sublimation, when a solid turns directly into a gas without becoming a liquid first.
“That water doesn’t stick around until snowmelt,” Pugh said.
Pugh and Eric Small, co-author of the study published in the journal Ecohydrology, also found that the snow under trees in the “red phase” melted up to a week earlier than the snow under healthy trees. The researchers believe the difference is caused by needles and branches falling onto the snow under red-phase trees. Those needles and branches absorb heat from the sun and reduce the snow’s reflectivity, causing the snow to melt more quickly.
The amount of runoff that comes from the snowpack in stands of dead trees is also higher than the amount of runoff from a similar snowpack under stands of live trees.