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QuestionHave there been shifts in abundance and distribution of alpine and sub-alpine plant species along an elevational gradient in an arid North American mountain range during the last half-century?

LocationElevational gradient in the White Mountains, California, USA (37 degrees 30N, 118 degrees 10W).

MethodsWe conducted a 49-yr re-survey of plant species distribution and abundance in areas originally surveyed in 1961. Species abundance data were collected along line transects between elevations of 2900 and 4000m. We evaluated the degree of plant community shift over time across elevations; specifically, we expected species ranges to shift upward such that species peak abundances would be observed higher in elevation in 2010 than in 1961. To address this expectation we conducted a permutational multivariate linear model analysis with elevation, soil type and year as factors. We further performed single-species analyses to evaluate how focal species contributed to the multivariate community-level shifts between 2010 and 1961, and how these varied across elevations and soil types. Growing season climate data (June 1 through October 31) collected between 1961 and 2010 were analysed to quantify the change in annual mean temperature and precipitation at this site.

ResultsWe found that Artemisia rothrockii increased in abundance at the upper reaches of its distribution between the 2010 and 1961 surveys. Additionally, we recorded significant declines in abundances in the lower elevation ranges of three alpine cushion plants: Trifolium andersonii, Phlox condensata and Eriogonum ovalifolium. These shifts coincided with a 0.98 degrees C increase in mean growing season temperatures and a 53mm decrease in mean annual precipitation between 1961 and 2010.

ConclusionsThese results suggest that rising temperatures and decreasing precipitation are negatively impacting alpine plant species while promoting expansion of sub-alpine species, possibly signalling the transition of this alpine plant community to sagebrush steppe.