Donovan Craig
Disturbances caused by roads and characteristics of native plant communities are two factors that may affect invasibility of communities by exotic species. We evaluated these factors by establishing permanent sampling sites along 13 roadsides in the Lake Mead National Recreation Area and adjacent public lands to determine the trends in microsite invasibility dependent upon distance from the road and species of native perennial. Sample sites were paired to include both gravel and paved roadsides. Five 100-meter transects were positioned parallel to each road at 10-meter intervals starting at five meters from the road. The first perennial plant species encountered along each transect were marked and if the species were re-encountered after the 50 meter mark, they were subsequently marked to include two of the same species per transect. The microsites under each perennial species were sampled for community composition. Additionally, percent cover of exotics and natives were recorded using cover categorizations within a 0.25-m2 frame around the center of the perennial plant. Six exotic species were detected throughout sampling. Schismus arabicus was the most frequently encountered exotic annual followed by Erodium cicutarium and Brassica tournefortii. Overall cover of exotic species declined slightly as distance from the road increased; however, differences were not significant. Over time, we will be able to monitor changes in the frequencies of both exotics and natives occurring in the microsites. This information will be of interest to managers and scientists alike in understanding exotic species invasions relative to roadways and possible associations with perennial natives.
Keywords: INVASIBILITY, MICROHABITAT, TRANSPORTATION CORRIDOR