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Remote Sensing Tools Preemptively Detect Drought-Stressed Pines with 80% Accuracy

Jeffrey pine.
Large swaths of dead trees across a landscape pose an extreme fire hazard, as seen in the southern Sierra Nevada range of California. Researchers developed a method that uses remote sensing and spectral sensing to pre-emptively identify drought-stressed trees. Forest managers can use this advance notice to prioritize management actions to lessen the risk of wide-spread tree mortality.
Fiscal Year
Research Unit(s)
Ecological Process and Function
Just as a high or low temperature alerts a doctor to illness in a patient, scientists have developed a method for taking a tree’s temperature to determine drought stress before the tree is showing other visible signs. Using existing USDA Forest Service remote sensors on a fixed wing platform, the newly calibrated and validated approach can detect tree drought stress across swaths of the forest.  Nancy Grulke and Charlie Schrader with the Pacific Northwest Research Station, Phil Riggan with the Pacific Southwest Research Station, and Jason Maxfield of Portland State University tested the efficacy of the method on Jeffrey pine, a species valued for timber. They used data from a remote sensing acquisition over the southern Sierra Nevada in California conducted at the onset of the severe 2013-2016 drought. The scientists found that imagery taken from an aerial platform with sub-crown resolution effectively identified drought-stressed trees within the context of other environmental stresses, such as air pollution or disease. In short, if the upper crown of a tree is cooler than mid crown at midday, or if the whole tree is “warm” relative to other trees, it suggests that the tree is drought stressed. This single trait identified drought-stressed trees with 80 %accuracy. Ozone and nitrogen deposition alter foliar pigments and tree crown structure in ways that also may be detectable with remote sensing acquisitions available to the USDA Forest Service. Remote sensing acquisitions commonly use high resolution and near-infrared wavelengths that yield forest data, and thermal imagery is becoming more readily available on some agency aerial platforms. Identifying trees and patches of trees at risk, located in microsites with insufficient or unreliable water availability and or already affected by insects, pathogens, or parasites, could inform forest managers in advance of tree mortality in severe droughts.   
Forest Service Partners
  • Pacific Southwest Research Station
External Partners
  • Jason Maxfield - Portland State University