Changes in landscape patterns associated with the persistence of aspen ( Populus tremuloides Michx.) on the western slope of the Rocky Mountains, Colorado

Abstract

Using repeat photography, we conducted qualitative and quantitative analyses of changes in forest cover on the western slope of the Rocky Mountains, Colorado, during the 20th century (80–100 years). For the quantitative analysis, paired images were classified using remote sensing and geographic information system (GIS) technologies. Comparisons were made using three landscape metrics: total relative cover; mean relative patch size; and number of patches per major vegetation type. We noted several important changes in the pattern of the landscape and the structure of the forests. The relative area covered by interspersed, non-forested rangelands has decreased significantly, and the total forest cover (both aspen, Populus tremuloides Michx., and coniferous types, primarily Abies lasiocarpa (Hook.) Nutt., and Picea engelmanii Parry) across these landscapes have increased significantly. Other landscape characteristics, such as patch number and patch size distribution also exhibit significant changes. These data reveal that in many cases, there has been important, observable change in the configuration of the landscape at many of these locations resulting in a decrease in the coverage of early seral communities and an increase in closed canopy forest communities. Currently, aspen has not been reduced in the extent of coverage in this region.