Non-Native Vascular Plant Inventory of Riparian Areas in Yosemite National Park, California

Kane, Jeffrey; Heath, Sacha; Kuhn, Bill

This is a report from a 2005 survey of non-native plants in riparian areas of Yosemite National Park. In 2005, Yosemite National Park (YNP) and the National Park Service Sierra Nevada Inventory and Monitoring Network contracted PRBO Conservation Science to conduct a non-native vascular plant inventory in riparian areas of YNP. Overall, 151 riparian plots in total were surveyed with 69 of the plots (46%) containing at least one non-native plant species. We also detected and identified a total of 59 nonnative plant species throughout all the survey plots. The mean number of non-native plant species per plot was 1.8 with a mean abundance of 1,137 per plot. Rumex acetosella, Bromus tectorum, Cirsium vulgare and Vulpia myuros had the highest frequency over all survey plots. Non-native plant abundances ranged from 1 – 40,000 plants per plot. Non-native species found in highest plant abundances were R. acetosella, B. tectorum, V. myuros, Bromus diandrus, Trifolium hirtum and Torilis arvensis. Of the plant community alliances encountered, the highest mean numbers of non-native species were located in the Populus balsamifera ssp. trichocarpa temporary flooded forest, Quercus chrysolepis forest, Alnus rhombifolia temporarily flooded forest and Pinus ponderosa woodland. Pinus ponderosa woodland had the highest mean abundance value, followed by Ceanothus integerrimus shrubland, Quercus chrysolepis forest and Populus balsamifera ssp. trichocarpa temporary flooded forest. Of the three most frequently encountered non-natives, B. tectorum was more likely to occur at lower elevation sites with less canopy cover. C. vulgare occurrences were best predicted by Cowardin class, elevation and stream order, while R. acetosella was more likely to occur at sites lower in elevation with a lower stream gradient.