Walnut Canyon Exotic Plant Inventory Database, WACA_Exotic_Plant_Inv.mdb

Southern Colorado Plateau Network; Hiebert, Ron; Hudson, Hillary

A survey of exotic plant species found within the Resource Preservation Zone of Walnut Canyon National Monument was conducted in September and October, 2008. A method was used that employed GIS techniques to generate a grid of the study area and then randomly select the number of grid cells that will result in a predetermined percent of the area one wants covered. Exotic plant presence/absence data were collected for each 150 m x 150 m grid cell. In addition, cover was estimated for exotic plants by species within a 6 m x 50 m belt transect within each grid cell. One hundred and five of 106 grid cells sampled contained at least one exotic plant species. Thus, no area of any size within the monument is devoid of exotic plant species. However, native vegetation remains dominant throughout the park, with the average cover of exotic plants at 1.75%. Nineteen exotic plant species were observed in the sampling grids. Average cover of all exotic species observed was below 4%. Species frequencies and cover were compared between lands within the original 1915 boundary, lands added in 1938, and those added in 1996. The highest average frequency of exotic species occurrence was within the boundaries of the original monument. Exotic species frequencies and cover were compared among four vegetation types: Riparian, Ponderosa Forest, Pinyon-Juniper Woodland, and Sparse Vegetation. Exotic species frequencies and cover were compared on the north versus the south side of Walnut Canyon. Prevention of new invasions and containment of existing infestations should be a top priority. Several species which are recognized as invasive plants that cause negative impacts were found in low frequencies in the park. These species should be targeted for control and monitoring. Monitoring should be concentrated on areas of known disturbance within or adjacent to the monument boundary.