Terrestrial Carbon and Nitrogen Eight Years after Bark Beetle-Caused Forest Mortality.

Recent epidemics of mountain pine beetle (Dendroctonus ponderosae) and spruce beetle (Dendroctonus rufipennis) have decimated at least 12 million hectares of coniferous forests in western North America. Such massive-scale forest mortality has caused shifts in carbon (C) and nitrogen (N) pools and fluxes between soils, plants, and the forest floor. Corresponding changes in future forest structure are likely to be affected, but the information on the early successional forest response is still limited and long-term response is unknown. Thus, the study assessed vegetation succession and terrestrial ecosystem C and N in subalpine-fir, Engelmann spruce and lodgepole pine forests eight years after the insect infestation. The study was established in the Snowy Range Mountains at 2896 meters elevation in south-central Wyoming. Soils are predominantly Entisols with minimal soil development, formed from mixed colluvium and metamorphic schist. Climate is cold and snowpack-dominated. Five clusters of dead and five clusters of live trees were selected in each type of forest. Samples were collected for total C and N determination of the understory vegetation (shoots and roots), soil (0–10 cm), and surface soil litter. Vegetation inventory were carried out in the middle of the growing season (July). All three forest types experienced 30–32% stand mortality. Eight years after the infestation, tree seedling density was two to ten times greater in infested areas with a greater presence of subalpine fir and loss of lodgepole pine from subalpine fir and Engelmann spruce-dominated forest types. Lodgepole pine forest was the only forest type with higher C and N contents (32-35%), which was mainly attributed to surface soil litter. Enhanced competition for soil resources between surviving trees, tree seedlings and understory vegetation will likely result in earlier onset of plant nutrient deficiencies, premature tree death, and new pests and disease outbreaks.