By Stephen Leahy

UXBRIDGE, Canada, Jan 22 (IPS)

Our trees are dying. Throughout the western United States, cherished and protected forests are dying twice as fast as they did 20 years ago because of climate change, researchers reported Thursday in the journal Science.

Fire did not kill these trees, nor did some massive insect outbreak. The trees in this wide-ranging study were “undisturbed stands of old growth forests”, said Jerry Franklin, a professor of forest resources at the University of Washington and one of 11 co-authors of the report.

“The data in this study is from our most stable, resilient stands of trees,” Franklin told IPS.

What this means is that the United States’ best forests are getting thinner.

It is like a town where the birth rate is stable but the mortality rate for all ages doubled over the past two decades. “If that was happening in your hometown you’d become very concerned,” said Nate Stephenson, an ecologist with the U.S. Geological Survey (USGS).

This dramatic increase of in tree mortality applies to all kinds, sizes, ages and locations of trees. In the Pacific Northwest and southern British Columbia, the rate of tree death in older coniferous forests doubled in 17 years. In California, doubling mortality rates took a little longer at 25 years. For interior states it took 29 years.

Mortality has increased in lock-step with rising temperatures of about 1 degree C in the last 30 years. Air pollution and ground level ozone were investigated and eliminated as the cause of the increased mortality, Stephenson told IPS.

Warmer temperatures in the west have meant the summer drought period is longer. The mountain snow pack contains less snow and melts much earlier in the spring. Warmer temperatures also favour insects like tree-damaging beetles. The combination of trees suffering moisture stress and a few more insect pests appears to be enough to tip the balance, said Tom Veblen of the University of Colorado at Boulder.

“We’re seeing continental-scale evidence of warming,” Veblen said. “It is very likely tree mortality will increase further as temperatures continue to rise.”

For complete article click: CLIMATE CHANGE: North American Trees Dying Twice as Fast.