Plant Community Response to Changes in Water

View of Owens Valley from the summit of Crater Mountain. The conversion of large basins to managed watersheds for the purpose of providing water through groundwater extraction and surface water diversions to urban centers has impacted semiarid ecosystems worldwide. Semiarid plant communities are adapted to short, regular periods of drought. However, human induced changes in the water balance remove these systems from the previously established range of water variability.

Owens Valley, California is an arid ecosystem that receives substantial runoff from the Sierra Nevada range, thus providing abundant water for human use, mostly exported to the City of Los Angeles. Surface water diversions and groundwater pumping in Owens Valley are part of a 140-yr land-use record, impacting the ecosystem in complex ways. Using satellite borne remotely sensed measurements (Landsat TM and ETM+) of vegetation cover over a 19-yr period, an extensive vegetation survey, field data and observations, precipitation records, data on water-table depth, and maps of historic land cultivation, we identified the key modes of response of xeric, phreatophytic, and exotic Great Basin plant communities to human manipulations of water resources.

Vegetation-groundwater relationship for 47 sites measured in 1992.In groundwater-dependent Alkali Meadow plant communities, we identified a threshold response to groundwater decline (see figure at left). The threshold corresponds to a shift from groundwater to precipitation driven dynamics as plant roots loose contact with the groundwater table.We also compared previously cultivated lands to non-cultivated lands and identified prominent floristic differences. Furthermore, vegetation cover on previously cultivated lands was found to be more variable in response to annual changes in precipitation. The results from this work broadly cover topics from remote sensing techniques to the ecology of Great Basin plant communities and are applicable wherever large regions of land are being managed in an era of changing environmental conditions.

Future work in Owens Valley will focus on understanding the permanence of changes in plant communities that were affected by groundwater pumping, and the consequences for water quality of removing the connection between plant communities and the groundwater table.

Groundwater is pumped directly into the Los Angeles aqueduct.

Related Publications:

Elmore, A.J., S.J. Manning, J.F. Mustard, and J.S. Craine. 2006. Decline in alkali meadow vegetation cover in California: the effects of groundwater extraction and drought. Journal of Applied Ecology, 43: 770-779. Nutshell Page

Elmore, A.J., J.F. Mustard, S.J. Manning. 2003. Regional patterns of plant community response to changes in water: Owens Valley, California. Ecological Applications 12(2): 443-460.

Project PI:

Dr. Andrew Elmore

Vegetation characteristic of Owens Valley. Many of these species rely on groundwater for growth throughout the dry summer months. Colleagues, Sara Manning and John Mustard, standing in a field of the invasive annual, Bassia hyssopifolia. Often, decreases in native vegetation were followed by an increase in exotic species when the drought ended.