Scale and Pattern of Cheatgrass (Bromus tectorum) Invasion in Rocky Mountain National Park

Cheatgrass (Promus tectorum L.), a winter-annual grass native to Eurasia, is one of the most widely distributed and damaging invasive annual grasses in North America. We studied the scale and pattern of cheatgrass in Rocky Mountain National Park, Colorado, examining possible dispersal and disturbance mechanisms and inherently susceptible environmental characteristics that may facilitate the spread of cheatgrass in the park. We distinguished facilitating factors related to land uses and natural processes. We mapped (with GPS) cheatgrass patches along randomly selected transects along roads, trails, in natural vegetation, and around developments. For each patch, we recorded: (1) patch size, (2) percentage cover of cheatgrass, (3) characteristics of microenvironments, and (4) amount of cheatgrass within microenvironments. Using MANOVA, we found that, at a broad scale, cheatgrass is concentrated on the east side of the park, at lower elevations, and in grassland and shrubland vegetation, with roads and developments in these areas having the highest abundance. Cheatgrass also is spreading into areas of natural vegetation, possibly due to naturally susceptible vegetation, fire, and favorable microenvironments. At a finer scale, cheatgrass is favored by cracks, cut banks, and untended vegetation near infrastructure. At the finest scale, we did not find that textured soils surfaces (e.g., rills, burrows, hoof prints) favored cheatgrass, but bare ground did. Based on our results, we suggest focusing control and management on areas where there is most potential to prevent further invasion, applying pre- and post- disturbance treatments where disturbances are planned, and planting invasion-resistant vegetation in areas of disturbance.