Document: AND-3-65-20

Semi-arid plant community response to drought and land use at the regional scale.

ELMORE, A.J.* ¹, J.F.MUSTARD ¹ and S.J.MANNING ²

Brown University, Providence, RI 02912 USA ¹
Inyo County Water Department, Bishop, CA 93514 USA ²

Abstract:
In Owens Valley, California we have quantitatively identified the regional extent of land cover change over the last 16 years and shown that semi-arid plant communities have distinct modes of response to climatic and anthropogenic stress. The 16 year data set was compared with maps of starting (1984) land cover, land use (current and historic), and soil type. Land cover changes were attributed to climate variability (an intense period of drought in the late 1980's preceded and followed by periods of sufficient rainfall) or predominant land uses (livestock grazing, irrigated agriculture, and groundwater pumping). Some meadow and shrub-meadow communities were largely affected by pumping and insufficient recharge and showed a greater than 50% decrease in live cover in more than 5% of the valley floor. An additional 20% of the groundwater dependent shrub and meadow communities were affected to a lesser extent by the same drivers. In many of these areas, the imposed stresses have resulted in a shift towards communities dominated by non-native annuals, rather than native perennial grasses and shrubs. Communities which were already dominated by annuals were least likely to be affected by pumping, but showed a strong dependence on annual rainfall. This response was observed over 10% of the valley floor. Within the limits of our observations, the remaining 65% of the valley was left largely unchanged despite low annual precipitation, primarily because these communities are either not dependent on groundwater or lie in regions of the valley where there was little change in the depth to groundwater over the 16 year study period. Quantitative analyses of land cover change provide an understanding of the consequences of disturbance on semi-arid ecosystems. In this study, we have shown that intense land use can result in a shift toward communities dominated by non-native annuals. In some areas, these communities did not return to natural vegetation despite minimal land use for nearly 100 years.

Keywords: semi-arid, plant community response, regional scale

This abstract is being presented at: 11:00 AM in session:
Oral Session #22: Multiple Disturbance Effects, Including Fire.