Sample Size Analyses for Soil Moisture and Root Biomass in Knuthsen Meadow, Carmen Valley, Sierra Nevada Mountains, California July 22-26, 2002

In the effort to determine if hydrologic restoration in Knuthsen Meadow affects root abundance and soil moisture, we gathered preliminary data to determine the optimal experimental design and sample size necessary to detect a 25% increase in root biomass and soil moisture following restoration. We found high variability in root biomass, with upstream meadow reaches having substantially greater variability than downstream meadow reaches. As a result, we recommend studying the effect of meadow restoration on root biomass separately in different meadow reaches. For examination of the effects of reach and restoration (between year effects) on soil moisture, a two-factor mixed model analysis with n = 8 would provide power greater than 80% for all hypotheses. Introduction The hydroperiod of Carmen Valley, California has been shortened by head cutting of the stream channel initiated by the construction of a rail line early in the 1900’s. The deepened stream channel that resulted from head cutting lead to more rapid drainage of the meadow after the annual snowmelt, and to the conversion of Carmen Valley from a series of wet meadows to drier meadows and sagebrush. Hydrologic restoration was completed in the Knuthsen Meadows section of Carmen Valley in late summer, 2001. A twelve-foot deep head-cut stream channel was eradicated and replaced by a series of ponds and earthen plugs that were designed to send overflow, winter-melt water directly onto the meadow in spring and early summer, and to provide a series of perennial catchment ponds throughout the meadow. In the effort to design a monitoring program to determine if, over time, the restoration will increase soil moisture and the biomass of plant roots, we gathered data on the abundance of plants roots and soil moisture by extracting soil cores within various plant communities.