Cascadia Prairie-Oak Weed Occurrence Survey – Initial Results

Invasive plants alter habitat structure and function, often reducing diversity and competing with or reducing habitat suitability for native plants and animals. Control of invasive weeds is critical to restoration of natural habitats and recovery of rare and listed species. As climate change and other factors create opportunities for the spread and introduction of new invasive species to make inroads on prairie and oak habitat in the Willamette Valley-Puget Trough-Georgia Basin (WPG) ecoregion, it’s critical that we share information across sites to identify trends and share lessons learned. To do this, the Center for Natural Lands Management (CNLM) set out to identify the distribution of species that are emerging issues to work toward more thorough control of present weeds and the prevention of new establishment.

Through discussion with prairie and oak habitat land managers in the WPG ecoregion, ten invasive species were identified as growing threats. CNLM conducted outreach to land managers throughout the Cascadia region to better understand the occurrence and response to these ten species. The survey asked respondents to describe the occurrence of these species on a site by site basis – including the species’ current prevalence, and what, if anything, site managers are doing to control the species and to what degree of success. The following maps were created using data from the initial 21 sites reported. As information is provided on more sites, maps will be updated and a report of the findings regarding distribution, threat level, and need for better identification knowledge as well as treatment techniques will be published.

Data was collected for the following invasive species: Amur honeysuckle (Lonicera maackii),  Salad burnet (Sanguisorba minor), Meadow foxtail (Alopecurus pratensis), Lesser celandine (Ranunculus ficaria), Japanese hedgeparsley (Torilis japonica), European blackberry (Rubus vestitus), Sterile brome (Bromus sterilis), Long-stalked cranesbill (Geranium columbinum), Rattail fescue (Vulpia myuros), Burrowing clover (Trifolium subterraneum).

Management guides for many of these species can be found here.