Yosemite's big trees withering away

There might be a scientific reason that the old-growth trees in Yosemite National Park don't seem quite as big or as plentiful as those in your grandfather's early snapshots of the park. The number of large-diameter trees - those at least 3 feet across - has dropped 24 percent over the past seven decades due to "moisture stress," according to scientists at the U.S. Geological Survey and the University of Washington. That is, they're parched - and global warming is a likely culprit, experts said. The die-off of these forest behemoths affects the appearance of a park that draws more than 3.5 million visitors a year. Scientists also worry it could affect wildlife, exacerbate climate change and stunt regrowth after wildfires. "Large trees do perform some unique functions," said Jim Lutz, co-author of the study and forest ecology researcher at the University of Washington. "Some vertebrates and mammals need large trees to nest in. If you're an animal of a certain size the tree has to be big."...SFChronicle