Initial and future stand development following mountain pine beetle in harvested and uncut lodgepole pine forests

Abstract

The extent and severity of over tory lodgepole pine (Pinus contorta Dougl.) mortality from mountain pine beetle (Dendroctonus ponderosae Hopkins) has created management concerns associated with forest regeneration, wildfire risk, human safety, and scenic, wildlife and watershed resources in western North America. In northern Colorado and southern Wyoming the long-term ecological and socioeconomic consequences of the outbreak hinge upon the response of tree regeneration in both harvested and untreated forests. To characterize initial and future forest development following mountain pine beetle mortality I conducted two studies. First, I used historic U.S. Forest Service stand and seedling survey records to compare the density and species composition of advance regeneration in uncut stands and post-harvest recruits in clearcut harvest units during pre-outbreak (1980-1996) and outbreak (2002-2007) period. Second, I compared the effects of various intensities of forest management on site conditions, seedling establishment and growth of advance regeneration to uncut areas in beetle-infested lodgepole pine stands. Advance regeneration averaged 3,953 stems ha-1 and was at least as high in beetle-infested stands compared to the pre-outbreak period. Lodgepole pine advance regeneration showed increased leader growth from 2008 to 2009 in harvested and untreated stands in response to canopy removal and decreased canopy foliage following overstory mortality. The density of seedling recruitment was three times higher in harvested than untreated stands (6,487 versus 2,021 seedlings ha-1), and did not differ between outbreak and pre-outbreak stands. Growth simulations showed uncut and partial cut stands will be dominated by subalpine fir (Abies lasiocarpa), while clearcut stand will be dominated by lodgepole pine and have attributes similar to pre-outbreak stands within a century.