USING GEOLOGY TO PREDICT SITES OF ANNUAL GRASS INVASIONS OR MAKE SURE THERE IS “GEO” IN YOUR “ECO”

Cheatgrass (Bromus tectorum) and other introduced annual grasses now dominant many plant communities in the western US. However, the distribution of these annual grasses is often patchy on both on a local and landscape scale. Recent research characterizing environments where cheatgrass does and does not occur showed that aeolian deposition, landscape position, and parent material, all of which influence soil texture and chemistry, can enhance or prevent cheatgrass invasion, regardless of past or on-going disturbance. At a landscape scale, cheatgrass was found to dominate the herbaceous layer in fine-textured soils with a high CEC. In sandy soils with a much lower CEC, cheatgrass distribution was found to be much more patchy. At a local scale in sandy loam soils, cheatgrass was found on on soils with higher CEC, higher silt content (and thus greater water-holding capacity), higher K/Mg, higher dust content, and in a lower landscape position than soils that did not support cheatgrass. Cheatgrass was not correlated with depth to buried soil horizons. Extrapolation of these findings to other soils and regions may enable us to better predict soils susceptible to cheatgrass invasion, as well as aid in native plant community restoration.