Giblin, David , Dunwiddie, Peter W. .
Vascular plant biogeography and floristics of the San Juan Islands.
Since 2005, we have conducted vascular plant surveys on more than 60 small islands (<40 ha) throughout the San Juan Archipelago of northwestern Washington State. To provide a comprehensive documentation of each islandís flora, voucher specimens were collected of all reproductive taxa, and lists were compiled that included all other species observed on each island. Furthermore, we visited islands at three different times during the growing season to maximize the probability of sampling the full suite of extant taxa. We have collected approximately 3,300 specimens to date, and our efforts have resulted in the publication of a previously undescribed Castilleja species endemic to the region (C. victoriae), the documentation of more than two-dozen previously unknown populations of rare species, and a comprehensive baseline dataset against which future changes in the islandsí flora can be compared. Overall, species richness showed a significant positive correlation with island size but not with distance to mainland. However, this relationship tended to break down among islands less than 0.5 ha in size, where we found evidence of the small island effect (SIE) reported by others. We also found strong differences in life history and dispersal strategies when comparing the most widespread native and introduced species. Results from these surveys offer valuable insights regarding the rate of spread of introduced species within insular ecosystems, illustrate the relative contribution that small islands make to biodiversity in this context, and provide future opportunities for examining the effects of climate change on insular temperate floras.
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1 - University of Washington, Herbarium, Burke Museum, Box 355325, Seattle, Washington, 98195, USA
2 - The Nature Conservancy, 917 1st Avenue, Seattle, WA, 98101, USA
Presentation Type: Oral Paper:Papers for Topics
Date: Monday, July 28th, 2008
Time: 4:30 PM