Assessment and Predictive Modeling of Individual Tree Mortality with Drone-Based Orthoimagery in a Southern Appalachian Red Spruce Forest, Whitetop Mountain, Virginia.

Keywords: drone imagery, tree vitality, southern Appalachian red spruce, logistic regression, Whitetop Mountain
Session Type: Virtual Poster Abstract
Day: Sunday
Session Start / End Time: 2/27/2022 05:20 PM (Eastern Time (US & Canada)) - 2/27/2022 06:40 PM (Eastern Time (US & Canada))
Room: Virtual 32

Abstract

Consumer-grade drones equipped with georeferenced optical sensors provide a cost-effective means to monitor individual red spruce (Picea rubens Sarg) vitality in globally rare Southern Appalachian red spruce forests. These mountaintop “Sky Islands” (< 1500m) are considered relicts of glacial climates and host species with current ranges much further north, like the federally-listed northern Carolina flying squirrel. Here, we demonstrate the applicability of RGB orthoimagery to (1) identify and monitor mortality status at the individual tree level and (2) train models such as logistic regression to predict instances of individual spruce mortality. Of 9,402 red spruce individuals assessed, 8,700 were classified as healthy (92.5%), 251 declining/dying (2.6%), and 451 dead (4.8%). We mapped the spatial distribution of spruce points by health classes (live, dead, & dying) and assessed patterns using kernel density. We found that site factors like tree height, slope, elevation, and flow accumulation, as well as density metrics from USGS-3DEP lidar, did not significantly predict instances of spruce mortality. Our study contributes to a better understanding of changing patterns of isolated spruce populations in the Southern Appalachians and elsewhere which may be especially useful in targeting areas where selective spruce culling and facilitated sapling release can increase overall stand health. These efforts are especially needed in light of regional and global climate uncertainty and subsequently predicted downslope migration of red spruce in the Appalachian region. Drone orthoimagery could also be useful to calibrate and validate spruce vitality predictions from high-resolution air- or space-borne remote sensing data.