WATER-TABLE INDUCED SHRUB-HERBACEOUS ECOTONE - HYDROLOGIC MANAGEMENT IMPLICATIONS

Environmental factors were investigated across a shrub-herbaceous ecot one (sharp zone of change) on a sloping site underlain by shallow grou ndwater on the arid floor of Owens Valley, California. Dominant plant species were salt rabbitbrush (Chrysothamnus nauseosus ssp. consimilis [E. Greene] Hall and Clements) and saltgrass (Distichlis spicata var. stricta [L.] E. Greene); typical of many similar habitats across the Great Basin. Historic air photographs were analyzed, and soil properti es, water table levels and shrub and herbaceous cover were measured at discrete sample points. To investigate soil and vegetation spatial pr operties, sample points were apportioned on both sides of the ecotone. Land management practices and fire were ruled out as causal factors f or the ecotone which remained stable through a 45-year period of air p hoto record. Soil textural, chemical and hydraulic properties were sim ilar across the ecotone and were uniform throughout the site. Only dep th to the water table changed significantly in a gradient perpendicula r to the ecotone. The shrub-herbaceous ecotone was located where the w ater table depth fluctuated periodically between 0.8 and 1.2 m; deeper water tables than this range favors shrub cover while shallower depth s favors meadow vegetation. When extrapolated to hydrologic management such as groundwater pumping, such a shallow depth and a narrow range of amplitude could restrict options for water development if maintenan ce of meadow vegetation is a goal.