Stressors and impacts

Since 2004, southwestern Colorado’s Engelmann spruce forests have experienced a severe outbreak of spruce beetles. Episodic outbreaks of spruce beetles have occured multiple times per century, and recent research indicates that they are related to multi-year drought. The combined effects of drought and beetle kill are weakening vegetation and making the forest more susceptible to wildfire, potentially impacting homes and local economies.

Monitoring forest changes with ForWarn

The interactive effects of multiple disturbances in this landscape are complex, however the combined effects of physiological stress from drought, beetle kill and wildfire appear to be transforming this forest into something far different than what it was a decade ago.

Early research in northern Colorado linked a beetle outbreak in the 1940s and 1950s to wind-damaged trees that enabled the population of spruce beetles to increase. More recent research suggests that, while local factors may be important, beetle outbreaks are linked to multi-year drought, which is in turn correlated with sea surface temperatures of the North Atlantic. Aerial photos and forest health surveys indicate that beetle infestation and mortality is a multi-year process that gradually thins tree stands over several years.

The interacting effects of physiological stress from drought, beetle kill, and wildfire are implicated in rapid transformations of several western forests. To study these threats and identify vulnerable locations, some forest caretakers use ForWarn—a satellite imagery-based forest disturbance monitoring tool. The tool provides maps comparing current forest greenness—a measure of vegetation health—with that of the previous year, the last three years, and the past decade.

When caretakers identify areas where greeness has declined in characteristic patterns, they can take actions to mitigate other stresses to the forest ecosystem. For instance, to reduce the risk of wildfire in vulnerable areas, forest officials may choose to manage fuel loads by removing or rearranging weakened vegetation. To decrease the chance of human-ignited fires, they might use an outreach and education campaign. In cases of extreme vulnerability, forest managers may decide to close the forest to public use until conditions improve.