Survey of rare and sensitive plants in recent acquisitions: San Juan Island National Historical Park (public version)

Martin, R.; Martin, Sam

doi:10.36967/2299979

The aim of this project is to obtain information on rare plant species of interest in two tracts of land that were recently acquired on San Juan Island, WA by the National Park Service. This information will be used to inform a vegetation management plan that will be developed for the San Juan National Historical Park. The tracts of land that are to be investigated are Mitchell and Westcott Bay in the English Camp unit. Due to the size of the two parcels and time constraints, this project did not include formal sampling methods such as transects or grids. Instead, the focus of the surveying was on specific vegetation types with the understanding that certain species may be found in specific vegetation types. Vegetation polygons were then searched via “focused intuitive control.” We used the current trail network as our sampling path, surveying more intensely in areas where rare species are more likely and briefly surveying unlikely habitats. We also focused on the trail networks because the most likely visitor impacts are along trails and where most vegetation management will likely occur. Out of the targeted list of twenty-seven species, we found three rare plant species in the Mitchell Hill unit: true baby stars (Leptosiphon minimus), Indian valley brodiaea (Brodiaea rosea), and shortspur white plectritis (Plectritis brachystemon). These species were associated with open bald habitats primarily on Haro-Hidden Ridge – Rock outcrop soils. Leptosiphon minimus was widely scattered across the bald habitats on the eastern upper slopes of Mitchell Hill. During our surveys in 2021 and 2022 we found at least several thousand plants widely scattered across the Mitchell Hill parcel. Because L. minimus is a cryptic species that is difficult to distinguish from Leptosiphon bicolor, the best resource on the distribution and identification of the species is Goodwillie & Stiller (2001). In 2022, we noticed many plants aborted their flowering stems prior to setting fruit. We did not observe any rare vascular plant species of conservation concern on the Westcott Parcel, and most the property has extensive evidence of prior human use and habitat alteration. There is a high-quality tidal salt marsh primarily composed of the pickleweed (Salicornia) and salt grass (Distichlis spicata). The forest communities appear to be highly used by walkers and hikers, with several established trails within the forested area. There is a small human-made wetland in the southeastern portion of the parcel, and a large established population of thistle that may be necessary to control.

Survey of rare and sensitive plants in recent acquisitions: San Juan Island National Historical Park (public version)

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