Distribution of exotic plant species and relationship to vegetation type at Bryce Canyon National Park, USA

Natural resource planning increasingly emphasizes control of undesired exotic plant species, which pose formidable challenges to conservation on many urban and wildland landscapes such as national parks. To enhance knowledge of exotic plant distribution and support implementation of an exotic plant management plan, we analyzed a data set including native and exotic vegetation on 406, 400-m2 plots within a 23,754-ha landscape encompassing Bryce Canyon National Park in southwestern Utah, USA. Fifteen exotic plant species inhabited plots, with the most frequent species all of Eurasian-origin: Poa pratensis (13% of plots), Taraxacum officinale (11%), Tragopogon dubius (8%), and Bromus inermis (5%). Relationships of exotic plant community variables (cover and species/400 m2) with vegetation map types at three hierarchical resolutions (coarse, with 8 vegetation types, intermediate with 14, and fine with 28) were strong. No single map resolution emerged as optimal overall for portraying exotic plant distribution, as different hierarchical map resolutions reflected heavily and minimally invaded vegetation types at all resolutions. Elevation was not consistently related to prevalence of exotic plants, as vegetation type within an elevation zone was paramount. For example, some high-elevation forest types (e.g., Populus tremuloides) supported more exotic plants than other high-elevation types (e.g., Pinus longaeva). Meadows were among the most invaded vegetation types, woodlands the least, and shrublands had variable prevalence of exotics depending on the specific type of shrubland. Results suggest that vegetation maps can aid landscape planning of management strategies, such as prioritizing early detection and treatment in vegetation types currently little invaded.