The number of dead trees on 750 million acres of public and private forests across the U.S. is on the decline for the second straight year largely due to the fact that the forests' scourge, the mountain pine beetle, is running out of its favorite food: the lodgepole pine.
The number of dead trees on 750 million acres of public and private forests across the U.S. is on the decline for the second straight year largely due to the fact that the forests' scourge, the mountain pine beetle, is running out of its favorite food: the lodgepole pine.
Acres of forests with dead trees due to the mountain pine beetle declined from 6.8 million acres in 2010 to 3.8 million acres in 2011 in Western states, according to a report released Monday by the U.S. Forest Service. This marks the second straight year with reduced mortality rates after steady increases between 2006 and 2009.
"Native insects and diseases run in cycles, and right now we are grateful the trend is downward," said U.S. Forest Service Chief Tom Tidwell. "While the news is good, we are certain to continue to face challenges, such as the effects of climate change and the introduction of invasive species. We must manage our lands across all boundaries to ensure the vitality and health of our natural resources."
Although Forest Service surveyors attribute some of the reductions to fewer available lodgepole pines, ponderosa pine and high-elevation white bark pine are still at risk. Also, the spruce beetle, the most significant natural enemy of the mature spruce, has caused four consecutive years of increased mortality, with dead spruce trees found on 428,000 acres nationwide. The fir engraver, common in Western coniferous forests, is responsible for tree deaths on approximately 323,000 acres, most of which are in California. Death of subalpine fir, caused by bark beetles and other mortality agents, was found on more than 274,000 acres.
In the East, tree mortality due to insects and disease remains low, with mortality caused by southern pine beetle at historically low levels. The southern pine beetle outbreak in New Jersey declined from 14,000 acres in 2010 to about 6,700 acres in 2011. Still, that lower number of acres is still considered very high for New Jersey, the Forest Service said, and invasive forest diseases and insects, such as the emerald ash borer and the Asian long-horned beetle, remain a big threat to Eastern forests.