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Bark Beetles and Forest Harvest in Oregon


In the dry Interior West, the pine forests that dominate many landscapes can experience widespread mortality during outbreaks of pine beetles.  The animation below shows one such outbreak occurring in south-central Oregon in the late 2000s.  The area captured in this image is roughly 20 km (about 13 miles) on a side. 

How do I interpret the colors?  In this false-color composite, denser forest appears green and open soil appears light pink. Sparse forests contain a mix of trees, shrubs, dead branches, and soil, and thus appear as a mixture of greens, browns, and pinks depending on the amount of each.  Clearcuts appear whitish pink because they remove most vegetation and expose bright soil, and then slowly fade back to green as vegetation grows back.  Fires also remove most vegetation, but fire scars darken the soil immediately after the fire, making them appear almost magenta.  

What about bark beetles? At the beginning of the animation, lodgepole pine forests in the middle to bottom third of the image appear pinkish green or brown. In 2007, 2008, and 2009, bark beetles killed large swaths of trees. Because tree needles turn red, then grey, and then drop to the ground, the greenish vegetation component of the colors disappears after bark beetles attack and only pinks and reds remain.  Unlike clearcuts or fire, most of the tree's skeleton remains to shade the ground surface, and branches and duff on the ground surface are not removed.   

Thus, the bark beetle outbreak appears as a darker reddish pink swath running throughout much of the southern half of the image after 2007.  You may want to pause the image in 2009 to see the condition of the forests in the most recent growing season. 

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