Surface energy flux consequences of bark beetle outbreaks in the south-central Rockies using MODIS data

Changes in canopy cover due to disturbance-related mortality have been shown to profoundly impact parameters within the surface energy balance and water budget. A shift in such fluxes can have consequences for surface temperature, cloudiness, run-off and stream flow, forest regeneration and net primary productivity. Current outbreaks of native bark beetles in western North America are some of the largest and most severe in recorded history. In recent outbreaks, bark beetles have reduced the basal area of host-dominated forests by up to 70%; with over-story mortality often exceeding 90% in mature, even-aged stands. The magnitude, frequency and intensity of recent outbreaks have been attributed to warmer summer and winter temperatures and drought conditions as a result of climate change. Such conditions both increase over-winter survival of bark beetle populations and create drought-induced stress on tree hosts. However, despite the likelihood that canopy mortality from bark beetle attacks will have profound effects on forest albedo and evapotranspiration; consequences for this disturbance type remain largely un-documented. This study addressed the question: how does a bark beetle outbreak event influence surface albedo and evapotranspiration? Seasonal patterns of surface temperature, albedo, evapotranspiration, and radiative forcing were modeled for lodgepole and ponderosa pine stands by outbreak age using Moderate Resolution Imaging Spectroradiometer (MODIS) data within the south-central Rocky Mountains. The prevalence of bark beetle outbreaks in high-elevation environments, which are exceedingly sensitive to climate change, necessitates the importance of understanding the energy and evapotranspiration consequences of such events.