The invasion risk in the Pacific Northwest of two closely related grass species in the Genus Cortaderia

Thesis (Master's)--University of Washington, 2016-08

The distribution of Cortaderia selloana and Cortaderia jubata in the Pacific Northwest (PNW) has not been examined on a regional scale although geospatial information exists. Cortaderia selloana continues to be sold in nurseries across Oregon and Washington and both species are used as landscape plantings. With invasive tendencies in California and abroad, and multi-age populations found across Washington and Oregon, what risk of invasion do these two species pose for the Pacific Northwest? Research efforts focuses on two questions: 1) Is there a pattern to distribution of Cortaderia occurrences/records that might help offer more evidence for the invasion risk to the Pacific Northwest? 2) What is each species’ potential for invasion in the Pacific Northwest? Two analyses were used to answer the above questions: geospatial and species distribution models. Geospatial analyses compared 83 existing records for both species with landscape features and other GIS data to find patterns or associations. Species distribution modeling was performed using a maximum entropy model program: MaxEnt. There are more C. jubata occurrences but they are mostly restricted to the mid and southern coast of Oregon whereas C. selloana is more likely to be found is more widely throughout the study area The majority of occurrences of both species were found in developed land cover types. There is a significant difference in the distribution of C. selloana and C. jubata with regard to distance to railroad, annual precipitation, and spatial location as measured by northing. Species distribution modeling outputs under current climate conditions indicate a broarder range for C. jubata than C. selloana. Both species increase potential areas of climate suitability under future climate scenarios. There does not seem to be a climate constraint for the future expansion of either species within the study area. It is likely that both species will continue to pose an invasion risk into the future. Early detection surveys should focus on developed areas, especially for C. selloana.