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Drought Effects on Soil Moisture in Canyonlands National Park

In arid ecosystems, plants depend on moisture stored in soils to support growth during the long periods between rainstorms. Desert plants have roots that are a few centimeters deep to, in some cases, many meters. Frequently, however, plants cluster their roots in the zone from 10-60 cm in soils. Below 10 cm, soils do not dry as quickly between rainstorms and by 60 cm, moisture from wintertime rains can remain in the soils for weeks to months. These deeper water stores help some desert plants survive the period between wintertime and late summer precipitation. In most years, these deeper soil layers are recharged during winter through rains and snows that percolate through surface soils. During the winter drought of 2001/2002, there was very little recharge into deeper soil layers and as we move into the dry summer season, soils are becoming progressively dryer. This drying trend may be reversed by late summer monsoons or could become increasingly severe if the monsoons do not materialize. Plants in the Canyonlands park are currently showing the effects of drought through reduced growth and/or germination. The USGS will continue to monitor soil moisture and plant moisture stress through the summer of 2002 as the drought persists. For additional information contact Prof. Jason Neff, Research Ecologist, Earth Surface Processes Team, U.S. Geological Survey, Denver, Colorado (also at University of Colorado, 303-492-6187).

Figure 1: Volumetric soil moisture in three different soil types near Squaw Flat Campground in Needles District, Canyonlands National Park. The three types of soils that contain varying levels of sand and silt, show different water holding capacity. All soils showed a pronounced drying trend during most of 2002.