USGS: large tree population declining in Yosemite
Posted: Thu Jul 30, 2009 6:23 am
FRESNO, Calif. – Scientists with the U.S. Geological Survey said Wednesday there are fewer large-diameter trees growing in Yosemite National Park than in years past, most likely because of climate change.
Warmer temperatures and smaller snow packs are creating conditions where fewer Ponderosa and sugar pines and other heartier trees can flourish, said Jim Lutz, a researcher at the University of Washington who co-wrote the study.
"Most of the water that becomes available in the Sierra Nevada comes from the snow pack," Lutz said. "Higher temperatures might increase populations of insects or make fungi more aggressive ... which all could increasingly contribute to tree mortality."
Lutz explained that when smaller snow packs collect in April and May, the trees have less water to sustain them in the dry summer months that follow. Warmer temperatures also can increase the severity of wildfires, which can kill off trees, he said.
Another factor in the decline may be that parts of Yosemite haven't experienced wildfires for 100 years. That could have allowed other species that compete with the bigger trees to survive and suck up the water large-diameter trees need to keep growing in girth, Lutz said.
http://news.yahoo.com/s/ap/20090730/ap_ ... mite_trees
Warmer temperatures and smaller snow packs are creating conditions where fewer Ponderosa and sugar pines and other heartier trees can flourish, said Jim Lutz, a researcher at the University of Washington who co-wrote the study.
"Most of the water that becomes available in the Sierra Nevada comes from the snow pack," Lutz said. "Higher temperatures might increase populations of insects or make fungi more aggressive ... which all could increasingly contribute to tree mortality."
Lutz explained that when smaller snow packs collect in April and May, the trees have less water to sustain them in the dry summer months that follow. Warmer temperatures also can increase the severity of wildfires, which can kill off trees, he said.
Another factor in the decline may be that parts of Yosemite haven't experienced wildfires for 100 years. That could have allowed other species that compete with the bigger trees to survive and suck up the water large-diameter trees need to keep growing in girth, Lutz said.
http://news.yahoo.com/s/ap/20090730/ap_ ... mite_trees