Sixty-five years of change in montane plant communities in western Colorado, USA

Documenting and predicting patterns of vegetation change over time are challenging due to a lack of sufficiently detailed historical data for comparison. Montane plant communities are expected to respond to anthropogenic disturbance, including climate change, in complex ways dependent on component species' responses to changing abiotic and biotic conditions. To investigate the patterns and possible causes of temporal changes in montane plant communities, we resampled 121 transects surveyed by Jean Langenheim from 1948 to 1952 in the East River Basin near Crested Butte, Colorado, U.S.A. Langenheim quantified the composition of the four predominant community types (sagebrush, spruce-fir, upland-herbaceous, and alpine) at sites ranging from 2600 to 4100 m in elevation. Our resurvey of the same sites 65 years later revealed that all four communities currently have much higher levels of heterogeneity among sites and have experienced significant changes in species composition and dominance. Compositional changes include significant increases in bare ground, graminoid and shrub abundance, and loss of forbs, at higher elevations. Species' mean elevations shifted upward 41 m, and many species expanded their ranges into new communities. Elevation shifts were most pronounced from lower elevation communities, while many alpine species shifted their ranges into lower subalpine meadow communities.