Riparian vegetation community response to over 80 years of de-watering, lower Owens River, California

Riparian areas in the arid western United States are critical ecosystem components that have been severely degraded over the last 100 years. This study examines how riparian vegetation along the Lower Owens River in eastern California has responded to over 80 years of de-watering, grazing, and other land uses. Riparian vegetation was sampled using line-intercept transects and 2m x 2m sub-plots in 2001 and 2002 to determine community composition and condition. Cluster analysis, Multi-response Permutation Procedures (MRPP), and Indicator Species Analysis (ISA) were utilized to determine 22 community types within the 104 km study area. Cluster analysis and Non-metric Multi-dimensional Scaling (NMS) were employed to examine relationships between community types along environmental gradients. Analysis revealed that community composition was strongly correlated with geographic and hydrologic gradients. Severely dewatered reaches were dominated by communities that have shifted from native to exotic vegetation. Five of the 22 distinct community types identified were dominated by exotic species, mainly salt-cedar (Tamarix spp.) and Russian thistle (Salsola tragus). These communities covered roughly 24% of the study area, mainly in completely dewatered reaches. Conversely, native communities remained resilient in reaches with small amounts of persistent water. The native willow (Salix spp.) wet meadow community exhibited the highest diversity measures, and represents a target community for restoration. The results of this study elucidate the shifts in riparian community type and composition following varying degrees of dewatering in an arid western stream system.