An annual aerial survey of forest health in Colorado shows the mountain pine beetle epidemic is slowing dramatically, at the same time the spruce beetle outbreak is expanding.
The infestation has impacted nearly 3.4 million acres (roughly 5,300 square miles) since the first signs of the outbreak in 1996.
This satellite image of an area near Grand Lake was taken before much of the damage occurred:
Six years later, the devastation is readily apparent.
The Coloradoan reports that Larimer County has been among the hardest-hit areas by both beetles. The mountain pine beetle infestation remains active from Estes Park to Leadville.
As one pest declines, another is on the rise
Meanwhile the spruce beetle outbreak spread to 183,000 new acres in 2012, bringing the total impact since 1996 to about 924,000 acres.
The two beetles – both Colorado natives -- are closely related, according to a report [.pdf] from the U.S. Forest Service. Their behavior varies though, with the most obvious difference being the tree species they attack. Spruce beetles require two years to complete their life cycle while mountain pine beetles typically complete a life cycle in one year.
Tiny insect's impact visible from space
NASA’s Earth Observatory notes that the beetle epidemic has caused so many trees to die that the impacts can be seen from space. A Smithsonian science blog says these kinds of satellite images used to be prohibitively expensive, but the U.S. Geological Survey began providing them for free in 2008.
Activity for both mountain pine and spruce beetles has increased as trees have been stressed by aging stands of dense trees, as well as by drought and warmer winters.
You can read the report here.