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RELATIONSHIPS OF MEADOW VEGETATION TO GROUNDWATER DEPTH: EFFECTS OF PRECIPITATION VARIABILITY AND STREAM INCISION
Citation:
CHAMBERS, J., W. TROWBRIDGE, D. G. JEWETT, D. GERMANOSKI, M. LORD, AND J. MILLER. RELATIONSHIPS OF MEADOW VEGETATION TO GROUNDWATER DEPTH: EFFECTS OF PRECIPITATION VARIABILITY AND STREAM INCISION. Presented at 2007 International Meeting of the Society for Range Management, Reno, NV, February 12 - 16, 2007.
Impact/Purpose:
To inform the public.
Description:
The composition of riparian meadow vegetation is controlled by access to groundwater. Depth to groundwater is controlled by meadow architecture and water source, and changes in either meadow architecture or water source through stream incision or changes in annual precipitation can cause major change in meadow vegetation. We have monitored the effects of yearly and seasonal variability in water tables and of stream incision on the composition and patterning of meadow vegetation in riparian meadows in central Nevada from four to more than 10 years. We installed peizometers along transects perpendicular to the stream channel and monitored changes in groundwater levels and vegetation at each peizometer. We classified the vegetation data into four community types using TWINSPAN and looked at the relationship between changes in groundwater depth and vegetation composition. We found that although water tables were spatially and temporally highly variable, both the elevation and variability of the water table were strong indicators of meadow vegetation type. The wettest types required the highest water tables and tolerated the least variability. Vegetation patterning was related to topographic position and groundwater sources and was influenced by stream incision and annual precipitation. Most community transitions tracked changes in annual precipitation. However, water table depths and vegetation close to the stream channel were influenced by stream incision. In actively incising reaches, vegetation plots showed consistent drying independent of precipitation changes. We suggest that the best indicators of change in these ecosystems include measures of stream incision such as can be obtained from cross-sectional data, and of the magnitude of the yearly and seasonal changes in water table depth from wells or piezometers. Vegetation monitoring should focus on riparian meadow species that require relatively high water tables and react quickly to short term changes in groundwater availability.