Vascular plant inventory tabular data for San Juan Island National Historical Park, 2001-2006. The objectives of the vascular plant inventories were: 1) to compile a vascular plant list for the park, 2) to verify the occurrence of at least 90% of the species through written records or voucher specimens, and 3) to describe prairie communities of American Camp.

Vascular plant inventories were conducted within San Juan Island National Historical Park between 2001 and 2005. The objectives of the vascular plant inventories were: 1) to compile a vascular plant list for the park, 2) to verify the occurrence of at least 90% of the species through written records or voucher specimens, and 3) to describe prairie communities of American Camp. Native species comprised 67% (268 species) of the total (400) and 70% of all species are perennial. The ratio of annual/biennial to perennial species varies greatly between native species and exotics. Approximately 17% of all native species are annuals or biennials while 57% of exotics are in this category. Three species, Symphotrichum hallii, Crassula connata, and Ranunculus californicus, documented within SAJH are listed as threatened by the Washington Natural Heritage Program.

Prairie plant communities at American Camp were inventoried using 1 m2 plots distributed randomly within five herbaceous communities described by Peterson (2002) and polygons that were delineated during the inventory as areas dominated by native species. Surveys were also conducted of soil seed banks to inform development of prescriptions for future restoration programs. Twelve plant communities were described including five that were dominated by native plant species: the Festuca roemeri (Roemer’s fescue) community, the Leymus mollis-Holcus lanatus (dune grass-velvet grass), Juncus balticus-Schedonorus pratensis-Juncus effuses (Baltic rush-meadow fescue-lamp rush), Lupinus littoralis-Bromus rigidus (seashore lupine-ripgut brome), Bromus sitchensis-Bromus hordeaceus-Poa pratensis (Sitka brome-ripgut brome-Kentucky bluegrass), and the Abronia latifolia (coastal sand verbena) communities. Five exotic species dominated the seedlings that emerged from soil samples in the greenhouse: Rumex acestosella, Holcus lanatus, Myosotis discolor, Aira caryophylla, and A. praecox. These species were found in all communities and did not reflect species that dominated the above-ground community.