Journal of Vegetation Science && (2015) Long-term changes in composition, diversity and distribution patterns in four herbaceous plant communities along an elevational gradient Gregory J. Sproull, Martin F. Quigley, Anna Sher & Eduardo Gonz alez Keywords Anthropogenic disturbance; Community diversity; Elevational gradient analysis; Elevational range expansion; Long-Term Ecological Research; Plant community ecology; Plant guild dynamics; Temporal change Nomenclature Kershaw et al. (1998) Received 23 May 2014 Accepted 11 November 2014 Co-ordinating Editor: Beverly Collins Sproull, G.J. (corresponding author, gregorysproull@gmail.com), Quigley, M.F. (martin.quigley@du.edu), Sher, A. (anna.sher@du.edu) & Gonz alez, E. (edusargas@hotmail.com) Department of Biological Sciences, University of Denver, Denver, CO 80210, USA Abstract Questions: Have species expanded their ranges upward in elevation? Have a- and b-diversity changed over time? Have species richness changes along the gradient shown distributional patterns? Have community compositions changed over time, and if so, which plant families are responsible for variation? Do her- baceous changes correspond to increased warming, overstorey shifts and distur- bance events at each site? Location: Long-term Ecological Research (LTER) sites near Niwot Ridge, CO, US. Methods: We surveyed four herbaceous plant communities along an elevation- al gradient for species composition, diversity and frequency. Our results were compared to those found in 1981 and 1996 in the same plots to determine long- term community change at each site and along the elevational gradient. We evaluated changes in elevational species range expansion, community diversity, and composition. We related herbaceous change to tree data and site-specific lit- erature on climate and disturbance to analyze change patterns and drivers. Results: Our investigation showed the upward range expansion of eight species. Alpha-diversity changes were site-specific, while species richness changes along the gradient did not exhibit distinctive patterns. Each community changed sig- nificantly (P < 0.05) in composition and in b-diversity. Shade-tolerant families increased in dominance at the three lower sites, which reflected succession-dri- ven canopy closure. Changes correlated to increased warming, overstorey shifts and disturbance. Conclusions: Herb aceous communities have changed in dynamic ways, as evi- denced by shifts in composition, diversity and distribution. We confirm the need for more long-term studies that can offer robust insights into the interplay between change drivers, such as climate, biotic interactions and disturbance, which work in concert to determine community assemblage. Introduction Plant communities are changing faster and more unpre- dictably in response to increased abiotic and biotic pres- sures (Parmesan & Yohe 2003; Root et al. 2003; Walther 2010). In mid- to high-elevation forests, plant community change has been particularly pronounced, as evidenced by shifts in composition, diversity and distribution (Klande- rud & Birks 2003; Lesica & McCune 2004; Pauli et al. 2007; Randin et al. 2009). At high elevations, heat toler- ance thresholds are narrower, acclimation potential is small (K€ orner 1999) and productivity is limited to a snow-free growing season (Price & Waser 2000). These sensitivities provide unique circumstances to observe the long-term effects of climate, biotic interaction and distur- bance on plant community processes and patterns (Wood- ward & Beerling 2013). Elevational gradient analysis is useful in understanding the patterns and drivers of such community changes at large spatial and temporal scales (Sundqvist et al. 2013). Along elevational gradients in mountainous herbaceous communities, studies have shown that species’ 1 Journal of Vegetation Science Doi: 10.1111/jvs.12264 © 2015 International Association for Vegetation Science