Vegetation Line Point Intercept Data, Owens Valley, CA USA 1984-2013

Each year, the Inyo County Water Department monitors vegetation conditions on the floor of the Owens Valley. The primary goal of this monitoring, according to the technical appendix to the Long-Term Water Agreement (Green Book) are to detect any significant decreases and changes in Owens Valley vegetation from conditions documented in 1984 to 1987. Vegetation live cover and species composition documented during the 1984-87 mapping effort were adopted as the baseline for comparison with each annual reinventory according to the Agreement. The reference measurements collected within individual areas mapped with similar vegetation (parcels) are referred to as baseline. The Green Book details certain decreases and changes in vegetation community types that must be avoided under the Agreement. Baseline vegetation communities in which evapotranspiration exceeds precipitation were classified as groundwater-dependent communities and are referred to as Types B, C, and D. These phreatophytic communities are dependent on shallow groundwater to maintain plant populations, as precipitation alone is inadequate to meet the water demand of these species. For these parcels, according to the Green Book, the goal is to manage groundwater pumping and surface water management practices so as to avoid causing significant decreases in live vegetation cover and to prevent a significant amount of vegetation from changing to a vegetation type that precedes it alphabetically (for example, Type C grass dominated meadow changing to type B shrub-dominated meadow). The goal is to manage the effect of pumping on the depth to groundwater to maintain baseline plant communities. A large proportion of groundwater-dependent parcels were mapped during baseline as Type C alkali meadows (61%), and the Agreement seeks to prevent these meadows from changing to shrub-dominated communities (Type B), a state change that is associated with increased depth to groundwater. Alkali meadows are of special concern because small increases in depth to groundwater can decouple the groundwater from the root zone of grass species.. Alkali meadow comprises 0.1% of the vegetation community types in California and 80% of alkali meadow communities in California are located within Owens Valley. Local management of water resources will be influential in determining the likelihood these ecosystems persist in California.