From: Allison Winter, ENN
Published September 19, 2012 10:55 AM

US Forest mortality declines due to lack of food for mountain pine beetle

Forests are not only threatened by man-made decisions like logging and development expansion, but also by insect infestation. From beetles to forest weevils, moths to borers and timber worms, insects cost millions of dollars each year in forest destruction from eating and living in these trees.

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Insects and diseases are important in maintaining a balance between healthy, functioning forests and catastrophic outbreaks and forest loss. These critical roles affect more than 750 million acres of forest in the US, as well as millions of trees in urban and residential areas.

However, lodgepole and ponderosa pine forests across western North America are actually in luck as tree deaths caused by insect infestation and disease declined significantly last year. A report by the US Forest Service attributes this decline to the mountain pine beetle, a native insect that has caused about 60% of the tree mortalities, who is starting to run out of food.

Researchers reported that about 6.4 million acres of forest died nationally in 2011, compared with 9.2 million acres in 2010 and a peak mortality of 11.8 million acres in 2009. Nearly 1 million acres have been affected in Montana, where other forests in Colorado, Idaho and Wyoming are suffering.

Usually non-native and invasive species are the pests we need to worry about. So why is this native critter multiplying and causing so much destruction? Well according to the report, warmer winters are not killing off beetle larvae. Researchers also say a critical factor in the decline has been a reduced number of available lodgepoles.

A single defoliation event does not usually cause tree mortality; however, taken together with continued attacks or severe abiotic factors, such as weather and drought, trees can succumb to these defoliating insects.

"Native insects and diseases run in cycles, and right now we are grateful the trend is downward," said US Forest Service Chief Tom Tidwell. However, forests will continue to face threats from new invasive species and climate change as different tree species will continue to be affected by different species of insects.

Determining the extent and intensity of insects and diseases will continue to be important for stakeholders and policy makers as it helps prioritize actions to be taken so forests can remain healthy and sustained for future generations.

Read the 2011 Major Forest Insect and Disease Conditions report at Scribd.com

Mountain pine beetle mortality on lodgepole pine image credit USDA Forest Service. 

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