Taxonomic, phylogenetic, and functional diversity of a Sierra Nevada subalpine meadow community along soil hydrological gradient

Israel Temitope Borokini , Megan Ramirez, Kiley S Smith

Mountain meadows occupy about 2% of the Sierra Nevada Range but house many narrow endemic and imperiled species. In this study, we investigated plant community structure and assessed species, phylogenetic, and functional diversity of Dog Valley Meadow, a subalpine meadow in the northern Sierra Nevada Range, California. Variation in groundwater level creates three distinct meadow-type habitats – hydric, mesic, and xeric types – making it an excellent system to investigate plant community structure at local scale along a hydrological gradient, while providing a complete floristic baseline data for conservation management and research. We estimated plant presence and cover or abundance in 341 1 m2 plots within 27 line transects separated by 10 m across the entire meadow. We computed several species, phylogenetic, and functional alpha diversity at plot and meadow type levels, as well as species and functional beta diversity measures along a soil hydrological gradient. The phylogenetic diversity calculations were based on a pruned chronogram phylogeny. We also conducted nonmetric multidimensional scaling (NMDS) to visualize species beta diversity and determined the local site and species contributions to beta diversity. Furthermore, we conducted indicator species analysis to investigate ecological fidelity of plants to meadow types, and assessed nonrandom species co-occurrences. We assessed the species nativity, growth form, conservation status, and response to grazing, and conducted a census of coniferous species in the meadow. We recorded 80 species across 23 plant families in the meadow, including 67 plants in the hydric, 55 in xeric, and 53 in the mesic habitats. Asteraceae and Poaceae were the most represented families in the meadow. The meadow community is dominated by native herbaceous and graminoid plants, only four of which are of conservation concern. The xeric habitats have the highest plot-level species diversity, phylogenetic diversity, and functional divergence. Hydric meadow communities have the highest and significant species dissimilarity from other meadow types, while mesic habitats have the highest functional beta diversity. A total of 37 indicator species indicates strong ecological fidelity across the three meadow types, and this drives 23% nonrandom species co-occurrences. The phylogenetic and functional diversity measures show that the meadow community is driven by phylogenetic clustering coupled with high functional divergence to facilitate resource partitioning. A roughly even representation of decreasers, increasers, and invaders in the meadow highlight post-disturbance vegetative recovery after historical grazing. We recorded about 300 conifer saplings and juveniles mostly in the mesic and xeric meadows, indicating recent encroachment associated with lower groundwater levels, driven by regional aridification. This baseline biodiversity data can support conservation and restoration efforts and facilitate future monitoring efforts in the meadow.