US forests hold new evidence of global warming
"Scientists see a trend in longer dry spells and winter snowpacks melting earlier than in the past.
Old-growth forests in the Western United States appear to be losing ground to the regional effects of global warming.
That’s the conclusion a team of federal and university-based forest ecologists have reached after looking at long-term trends in patches of relatively pristine old-growth forests. The study sites range from northern Arizona and north central Colorado to the Olympic Peninsula and southern British Columbia.
Over the past 50 years, trees large and small in these tracts – largely untouched by wildfires or beetle infestations – have been dying at an increasing rate. And the rate at which they are being replaced has not changed. If the trend continues, researchers say, forest age, average tree size, and carbon-storing capacity of these areas will gradually fall.
After examining a range of possible causes for the region-wide pattern, the last ones standing are the West’s warming trend and warming’s effect on the amount of water these areas receive. Summer dry spells are longer. Snows melt earlier. More winter precipitation falls as rain, rather than snow, and the snow that falls has a lower water content than it once did."
"If the trends continue, they have implications for the region’s efforts to adapt to climate change, adds Thomas Veblen, a biogeographer at the University of Colorado at Boulder. Particularly when the underlying die-off is accelerated by insect infestations, wildfire managers will have to rethink their strategies for reducing wildfire risks, including current policies that encourage people to build large housing developments in wildfire-prone areas.
In addition, the changes are making wildlife conservation efforts more difficult to plan.
Often, conservationists set a target by learning what an area was like in the distant past, then they try to re-create that, says Nathan Stephenson, also with the USGS research center in Three Rivers, Calif. “As climate changes and other environmental changes happen, the past may no longer be the best model for the future. We may switch from trying to keep a snapshot of the past to efforts to help guide things into the future while sustaining old forests.”
For Franklin, even that may be too gentle. “So much of conservation is focused on going back or keeping it as it is,” he says. Faced with a warming climate, “you can’t go home.”
US forests hold new evidence of global warming / The Christian Science Monitor - CSMonitor.com