SHORT-TERM AND LONG-TERM PATTERNS OF SOIL-MOISTURE IN ALPINE TUNDRA

Time domain reflectometry (TDR), a nondestructive technique for monito ring water content of soils, was used to measure volumetric soil moist ure in three different communities in the alpine tundra during the sum mer of 1992. Data were converted to gravimetric estimates in order to allow comparison with 20 yr of records of gravimetric data, some of wh ich date back to 195 3. Analysis for growing-season trends indicated p rogressive depletion of soil moisture in all three community types stu died. Using a linear model, mesic meadows showed the strongest seasona l decline and wet meadows the weakest. Curvilinear fits of the data su ggested midsummer minima in xeric and mesic meadows and a midsummer ma ximum in wet meadows. Average summer soil moisture values for xeric me adows during the 1953-1964 interval were lower than those made in late r years. This result may reflect sample site differences, but is consi stent with a directional trend in increasing precipitation over this i nterval. Average summer soil moisture content of xeric meadows was cor related with annual precipitation, but not growing season (June-August ) rainfall; this pattern was only discernible with the 20 yr data set.