A Geospatial Analysis of Bark Beetle-Induced Wildfire Risk Zones in the Okanogan Wenatchee National Forest

Marco Allain

doi:10.11648/j.aff.20170601.15

Abstract

Over the past 30 years mountain pine beetle (MPB) outbreaks have become widespread throughout the western US and Canada. MPB attacks leave acres of dead trees that may predispose forest landscapes to large fires. With the use of field work and geospatial technology, these outbreaks can be better mapped and assessed to evaluate forest health. This study is designed to map and classify bark beetle infestation in Washington's Wenatchee National Forest. Field work on seventeen randomly selected sites was conducted using the point-centered quarter method. Recent MPB outbreak areas were classified using National Agriculture Imagery Program (NAIP) imagery. A link between MPB attack and forest fires was then quantified using MODIS fire data. Lastly, a predictive infestation model was constructed using the following geophysical parameters: disturbance indices, Landsat TM5 classification of groundcover as well as vegetation stress using hyperspectral data. Selected imagery from the Hyperion sensor was used to run a minimum distance supervised classification in ENVI, in attempt to detect the early “green stage” of infestation. This study detected MPB spread and assessed the fire risk related to infestation.

Highlights

A legacy of fire exclusion and increased incidence of summer drought in the western US has predisposed forested landscapes to bark beetle outbreaks [15, 1]
Since bark beetles kill the tree they infest, increased infestations result in an abundance of dead biomass, which may lead to increased risk of wildfires [33]
The Landsat classification and the National Agriculture Imagery Program (NAIP) algorithm were used to detect infested sites in the study area. These infested sites were overlaid atop Moderate Resolution Imaging Spectroradiometer (MODIS) fire data to establish a link between infestation and wildfires

Summary

Introduction

A legacy of fire exclusion and increased incidence of summer drought in the western US has predisposed forested landscapes to bark beetle outbreaks [15, 1]. Bark beetles preferentially attack trees that showcase two favorable characteristics; nutrient content and trunk diameter thickness [32]. These factors are thought to attract beetles which bore into trees and deposit their larvae. Bark beetles are most successful when attacking trees that have been weakened by disease, drought, smog, previous infestations or physical damage.

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Conclusion