Forest disturbance is increasing globally due to human-caused changes in land use and climate. In the Rocky Mountains, bark beetles have become a major agent of change. Over the past two decades, the spruce beetle has disrupted forests in British Columbia, Canada, Alaska and the western United States. Currently infestations cover 166,000 hectares [410,195 acres] in the western United States, with 84,000 hectares [207,568 acres] in Colorado and 32,000 hectares [79,000 acres] in Wyoming. Spruce beetle epidemics are not new to the Rocky Mountains but the potential for outbreaks is expected to rise under climate change.
Rocky Mountain Research Station scientists conducted a study at the Glacier Lakes Ecosystem Experiments Site (GLEES), a high-elevation watershed research site located in the Snowy Range of southeast Wyoming, to determinehow a spruce beetle epidemic causes ecosystems to use less carbon and water.
As spruce beetle impacted 75 percent of the forested basal area at GLEES, ecosystem water use declined 30 percent while a 50 percent reduction in photosynthesis ultimately turned the forest from a carbon sink to a carbon source.
The dynamics of the ecosystem response to the epidemic could not adequately be described by mortality alone, rather the physiological response of impacted spruce trees must also be taken into account.
These results improve our fundamental understanding of how a major forest disturbance can impact ecosystem function and use of carbon and water.