Reconstruction and spatial analysis of alpine treeline in the Elk Mountains, Colorado, USA

Abstract

The alpine treeline is a biogeographic transition zone that is an important indicator of environmental change. Here, I analyze spatial and temporal dynamics of vegetation in the alpine treeline ecotone in the Elk Mountains of western Colorado. I used dendroecological techniques to determine dates of tree establishment, then reconstructed past forest structure and composition and documented the patterns of vegetation change. The elevation of treeline in the Elk Mountains has not advanced upslope for at least 130 years, but tree density and basal area in the alpine ecotone have more than doubled during the 20th century. Spatial patterns of tree establishment are significantly clustered across multiple spatial scales in the alpine zone, while tree distributions in the subalpine forest have shifted from random to clustered patterns. Overall the pattern of treeline dynamics has been different from other sites in the Rocky Mountains where upslope advance has been more prominent. This research highlights the importance of site-specific information to understand variability in the spatial and temporal dynamics of treeline.