Early Detection of Invasive Plant Species in the San Francisco Bay Area Network: A Volunteer-Based Approach

Williams, Andrea; O'Neil, Susan; Speith, Elizabeth; Rodgers, Jane

Three objectives provide the framework for early detection monitoring: developing and revising a list of target invasive plants, whose priority determines the level of data gathered; ranking park subwatersheds by management priority, risk, and current infestation level to generate priorities for monitoring frequency; and regularly evaluating and examining invasive plant monitoring data to revise and refine priorities, as well as clarifying contributing factors to new invasions in the park. The list of target species for each park was based on current knowledge and rankings, summing recognized invasiveness and biological ease of control and stratifying into priorities by feasibility of control based on species’ infested acreage in the park. A list of all exotic species known or thought to occur in the parks (~300 species; see Appendix A), compiled from NPSpecies, was the base list. After removing known non-invasive species, and species locally non-native, 174 species remained. Species listed by the California Invasive Plant Council (Cal-IPC), California Department of Food and Agriculture (CDFA), The Nature Conservancy (TNC), and local Weed Management Areas received varying numbers of points for invasiveness, as did unlisted species which shared invasive characteristics with a listed congener. Based on best available knowledge, species also received points for altering ecosystems—affecting a system change, not just crowding out other plants—and for endangering rare plants in SFAN parks. Next, based on best available knowledge, species were ranked by ease of control independent of number of acres infested. All points were summed for the overall invasiveness score, then sorted according to feasibility of control based on number of acres infested with that species, cost for removal, politics, and access. “Controllable” acreage was based on the size of the park unit and annual area treated by their exotics program, and varied slightly by park. Species shown to be highly invasive, but not widespread in the park, are top priority for detailed mapping; more widespread but still invasive species are mapped with a point unless populations are small. The list of priority areas for searches was made by ranking subwatersheds—drainage-based subunits of watersheds—by number and degree of current infestations; risk of further infestation; and priority of resources present. Subwatersheds were ranked, grouped along the most natural breaks, and assigned a score. Total score was obtained by adding risk to weighted (2x) rare species priority score and subwatersheds approximately quartered into high, significant, moderate, and low priority. High-priority subwatersheds are visited annually; significant and moderate, biennially; and low, once every five years. Surveys cover roads and trails, with data collection ranging from simple (presence/absence during a survey) for low-priority species or Level 1 volunteers to complex (digital point and polygon data, as well as associated phenological and habitat data, taken with a handheld unit) for highly skilled volunteers and staff and high-priority species. Information is stored in GeoWeed, Sonoma Ecology Center’s improvement on The Nature Conservancy’s Access-based vegetation management information system WIMS. GeoWeed (http://geoweed.org), like WIMS, is freely available and allows for digital data collection through a series of ArcPad forms. Negative data are tracked through the use of the “Survey Area” portion of the database.

Early Detection of Invasive Plant Species in the San Francisco Bay Area Network: A Volunteer-Based Approach

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