Surveyed acres of mortality from 1998 to 2011; source U.S. Forest Service
Surveyed acres of mortality from 1998 to 2011; source U.S. Forest Service

WASHINGTON - Invasive insects like the mountain pine beetle, emerald ash borer and Asian long-horned beetle continue to be a deadly menace to the nation's forests but the overall number of trees being killed by these pests is on the decline.

According to the U.S. Forest Service's report, Major Forest Insect and Disease Conditions in the United States, the number of dead trees surveyed on 750 million acres of public and private forests across America declined for a second straight year in 2011. The report indicates that the number of dead trees attributed to insect infestation declined from nearly 12 million acres in 2009 to just over 6 million acres last year.

This decline is most evident in the western states where damage wreaked by the mountain pine beetle declined from 6.8 million acres in 2010 to 3.8 million acres in 2011. The Forest Service report explained that this sharp decline resulted "largely because the insect is running out of its favorite food source: lodgepole pine."

"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."

The report tracks activity of various tree-killing bugs, including:

* 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;

* Bark beetles and other "mortality agents" caused the death of more subalpine fir on more than 274,000 acres;

* The southern pine beetle outbreak in New Jersey declined from 14,000 acres in 2010 to about 6,700 acres in 2011. However, that lower number of acres is still considered very high for New Jersey. Invasive forest diseases and insects, such as the emerald ash borer and the Asian long-horned beetle remain a big threat to eastern forests.

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