An Exploration of Alpine Floristic Diversity Among Eight Peaks in the Eastern Sierra Nevada of California

To determine patterns and drivers of alpine floral diversity in the eastern Sierra Nevada of California, community composition was investigated on 8 peaks along a latitudinal gradient. The diversity of alpine flora can be attributed to both macroenvironmental factors such as latitude and elevation, and microenvironmental factors such as substrate and aspect. Using the point-intercept method vascular plant species abundances were documented, along with growth-form composition, elevation, latitude, aspect, slope, parent substrate, and substrate grain size. Diversity, dominance, and community similarity/dissimilarity were explored. Across the Sierra Nevada, alpine communities were highly dissimilar from each other (83.2%) and were divided into two distinct assemblages separated by elevation (near-treeline and near-summit) with a 91.3% dissimilarity. In addition, near-treeline sites were more dissimilar in floristic composition (66.0%) across the Sierra Nevada when compared to near-summit sites across the mountain range (34.4% dissimilarity). There was stronger dissimilarity among sites on individual peaks (range: R=0.56-1.0; P=0.0043-0.0001) than among peaks across the range (R=0.29, P=0.0001). The six environmental and topographic variables collectively explained 54.8% of the floristic dissimilarity in community assemblages across the mountain range, with substrate grain size having the largest influence (R2=0.29, P=0.0001), followed by aspect (R2=0.24, P=0.0001) and elevation (R2=0.15, P=0.0001). Aspect had the largest influence on community composition on the northern and central peaks, while substrate grain size had the largest influence on the two southernmost peaks. On individual peaks, floristic dissimilarity occurred over short elevational distances shown by large changes in beta-diversity. Species richness and diversity did not significantly differ across the range, while percent cover increased with increased latitude, coinciding with more precipitation in the northern region and drier habitats with less available optimum range in the southern region. The southern region had a higher proportion of endemic species. Further research efforts should be directed towards monitoring species existing in the climatically decoupled microhabitats created by variations in substrate grain sizes.