From: NASA Earth Observatory
Published July 20, 2016 10:37 AM

Quantifying Tree Loss in Sierra National Forest

Mass tree die-offs are sparking worries of fire in California’s Sierra Nevada range. An outbreak of bark beetles, along with persistent drought in the state, have caused many evergreen trees to wither and die.

The damage spread rapidly through the mountains in the fall of 2015 after favorable spring conditions (warm and dry) led to a surge in beetle populations, according to Zach Tane, a remote sensing analyst with the U.S. Forest Service (USFS). The beetles burrow under a tree’s bark and lay their eggs. Once they penetrate the tree’s armor (the bark), they begin to gnaw into its living tissue, the phloem.

“Needles don’t turn red the next day. It’s a slow process of the tree dying, and it has to do with life cycle of bark beetle and how long needles can persist in a green state,” said Tane. “As the population of beetles grows, they can overwhelm the natural defenses of a tree. There’s a tipping point—that’s what happened in Colorado and probably what’s happening here.”

There has never been an outbreak of this magnitude recorded in the Sierra Nevada, according to Tane. The maps above depict some of the damage as observed by NASA’s Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) instrument. AVIRIS is an optical sensor that collects data in 224 spectral bands, ranging from visible blue (0.4 µm) to shortwave infrared (2.5 µm). Researchers can make inferences about tree health from the way the leaves absorb and scatter light.

Read more: http://earthobservatory.nasa.gov/IOTD/view.php?id=88381&src=eoa-iotd

Image: NASA Earth Observatory map

Credits: Joshua Stevens via http://earthobservatory.nasa.gov/IOTD/view.php?id=88381&src=eoa-iotd

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