Changes in soil physical and hydrological properties due to Bromus tectorum (cheatgrass) invasion

Introduction of Bromus tectorum (cheatgrass) into western rangelands has had a profound effect on the diversity and health of native ecosystems. Introduced in the late 19th century, B. tectorum has rapidly out-competed native species and colonized large areas of the Great Basin region (Mack, 1981). The objective of this research is to assess changes in soil physical and hydrologic properties on former A. tridentata sites now invaded by B. tectorum and to quantify the scope of the alterations through time. Study site selection was based upon a range of A. tridentata stand replacing fire histories spanning approximately 20 years and subsequent colonization of each fire site by B. tectorum. Fire sites sampled were invaded by B. tectorum following a single fire event; the earliest plot was burned in 1985 with subsequent sites having fires in 1987, 1998, and 2002. Sites characterized by A. tridentata, and not burned, were sampled as controls. To assess soil physical and hydrological properties measures of aggregate stability; hydrophobicity; bulk density; surface strength; surface roughness; and infiltration (double-ring and tension infiltrometer) were made. T-test results indicate increased silt and clay particle size fractions and a decreased sand particle size fraction with colonization by B. tectorum. B. tectorum sites exhibited increased bulk density, aggregate stability, and surface strength along with decreasing surface roughness and saturated conductivity. No significant differences in unsaturated conductivity were represented by tension infiltrometer measurements. Sand sieve fractions indicate an increase in very coarse, coarse, and medium sand fractions and a decrease in fine and very fine sand fractions on B. tectorum sites. Results suggest that B. tectorum invasion is altering soil physical properties and in turn, surface hydrology