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  • Thumbnail for Causes and Consequences of Alpine Shrub Expansion on Pikes Peak, Colorado
    Causes and Consequences of Alpine Shrub Expansion on Pikes Peak, Colorado by Wheeler, Audrey Renee

    Alpine ecotones are often used as sites for measuring ecological responses to environmental changes. Recent decades of human-induced climate change have had a measured effect of increasing the altitude of alpine treelines in areas with increasing regional summer temperatures. On Pikes Peak (Southern Rocky Mountains, Colorado), there has been a measured treeline advance in the past several decades. The purpose of this study is to determine whether alpine willow shrubs on Pikes Peak are also advancing upslope in response to recent climate warming trends. After sampling ~300 shrubs in linear transects directed upslope, the shrubs were aged by counting and measuring annual growth rings. There is a significant negative correlation between shrub age and elevation for shrubs on the bottom of the valley (p=0.015). The mean shrub age decreases with increased elevation, and the ages in the lowest elevation band are significantly different from those in the highest elevation band for valley shrubs (p=0.041). The width of annual growth rings did not appear to have a correlation with annual or growing season temperature anomalies. A photographic analysis of aerial photographs from the past several decades was inconclusive. This study suggests that shrubs are increasingly recruiting at higher elevations on Pikes Peak, and have perhaps spread to their current elevation within the past 30 years. By surveying shrub movement in alpine environments, extrapolations can be made about how shrub distribution will change in the future and how shrubs may contribute to feedback cycles for regional climate phenomena.