PREDICTING PLANT NATURALIZATIONS IN THE PACIFIC NORTHWEST: THE FATE OF BAMBOOS IN THE UNDERSTORY OF CONIFEROUS FORESTS
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Identifying future plant invaders could drastically reduce the economic costs and environmental damages these species inflict annually. As an addendum to Weed Risk Assessments, I erected and tested a series of pre-introduction screening procedures to detect plants with a high likelihood of naturalization. Temperate East Asia is a large source of horticultural imports and is the largest single remaining source of new horticultural imports and potential plant invaders. The Pacific Northwest and temperate East Asia share many physiognomic, floristic, and climatic similarities - a connection that renders the Pacific Northwest vulnerable to plant invaders from temperate Asian forests. Despite the apparent vulnerabilities to Pacific Northwest forests, they remain unaffected by major plant invaders. To conserve these forests, potential plant invaders must be detected and thwarted before they proliferate and spread. Bamboos are prominent in temperate coniferous and broadleaved forests in Northeast Asia but are an absent life form in the Pacific Northwest. I evaluated experimentally the likelihood of temperate Asian bamboos to naturalize in Pacific Northwest forests. Six species of Asian bamboo and one species of native North American bamboo were subjected to tests that examined their tolerance to shade and drought. Arundinaria gigantea, the native North American bamboo is inhibited by both low light and drought in the Pacific Northwest. Bashania fargesii and Sasa kurilensis also showed limitations to naturalize under shade regimes in Pacific Northwest forests. In contrast, Pleioblastus chino, P. distichus, Pseudosasa japonica, Sasa palmata and Sasaella ramosa were unaffected by drought water and low light regimes. Neither drought nor low light will apparently inhibit the establishment of these five species of Asian bamboos in Pacific Northwest forests. If bamboos naturalize in Pacific Northwest they will eventually undergo mast flowering. During this flowering, bamboos can produce massive amounts of seed that that are gorged upon by rodents. I tested the effects of bamboo seeds on the native Pacific Northwest deer mouse (Peromyscus maniculatus), a Hantavirus carrier. Deer mice readily consume bamboo seeds and undergo high fecundity. Temperate Asian bamboos are potential future invaders in Pacific Northwest forests, with ominous consequences; their continued importation should be subject to increased scrutiny.