Subalpine Tree Demography and Climatic Variation in the Colorado Front Range

SMITH, J, J PARITSIS,TT VEBLEN

Boston, MA, EE.UU.

Congreso; 2008 Annual Meeting of the Association of American Geographers; 2008

Association of American Geographers

Long-term data from permanently marked tree populations are essential for evaluating the effects of recent climatic variation on tree mortality and recruitment patterns. In this study we address the temporal patterns of tree mortality in subalpine forests in the Colorado Front Range and how these patterns are associated with climatic variation. Ten permanent forest plots initially established during the 1980s in the subalpine zone in Boulder County were re-measured for mortality, recruitment, and radial growth during the summer of 2007. Each plot ranging in size from 324 to 2916 square meters contains an average of over 400 permanently tagged and mapped trees (> 4 cm dbh). Six plots represent a topographic-moisture gradient of old (i.e. > 300  years) stands at xeric sites dominated by limber pine or lodgepole pine to mesic stands of Engelmann spruce and subalpine fir. Four plots are relatively even-aged (c. 100 to 120 years old) post-fire stands of mainly lodgepole pine. To supplement the 1982-2007 data on tree mortality from direct measurements, all standing dead and fallen but preserved dead trees were cored for determination of death dates using dendrochronological methods. Tree mortality rates were highly variable at annual and decadal time scales, and higher mortality was associated with episodes of warmer and drier conditions like those recorded during the late 20th to early 21st centuries. These results contribute to the understanding of subalpine forest dynamics, particularly in the context of recent climate change.