Woodlands dominated by pinyon pine and juniper have been expanding across the sagebrush-steppe since the turn of the century and currently occupy over 690,000 square miles. The problem of woody plant encroachment into areas formerly dominated by shrubs and grasses is pervasive throughout the western United States. However, in the Great Basin, water is more limited than some other semi-arid regions, which leaves the central Great Basin poised to exhibit greater sensitivity to environmental change.
In semi-arid landscapes the type and amount of woody plant cover can affect water, soil and plant interactions by altering:
- The distribution of vegetation and canopy cover across the landscape;
- Increasing bare ground and soil erosion; and
- Plant species composition or diverisity and production.
These changes can produce differences in the amount of surface runoff, soil infiltration and moisture, evaporation, and transpiration.
In pinyon-juniper woodlands, large bare ground areas can have up to 24 times more soil loss than areas protected by plant cover. The decrease in soil moisture due to increased run off may be further manifested as decreases in stream flow and groundwater levels.
In water-limited systems a primary motivation for reducing woody vegetation is the possibility that water-savings will be realized, providing increased water for shrub and herbaceous species production, and increased spring flow, stream flow, and groundwater levels.
The objective of this research is to determine the effects of pinyon-juniper presence or removal treatments on various components of the water cycle, particularly tree water use, soil moisture, evaporation from plant canopies, rainfall interception by tree canopies, surface runoff and groundwater recharge.