Historical Changes in the Physical and Vegetational Characteristics of Protection Island, Washington

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Protection Island National Wildlife Refuge, WA, is home to the majority of breeding seabirds and harbor seals found in the Puget Sound/San Juan Island area. The island consists of a high central plateau flanked by bluffs on the north and south and by low points on the southwest and east. We analyzed the physical and vegetational changes in Protection Island from the 1860s to 1999, an interval spanning an early period of agricultural use followed by intensive subdivision into building lots and then conversion to a refuge. During that time span Kanem Point on the southwest had shortened and Violet Point on the east had lengthened. The tall northwest bluffs, which experienced rapid erosion early last century, had steepened and stabilized. Little change had occurred on the northeast and southern bluffs or on the bluffs over the points where many seabirds nest. On the upper plateau, forested areas had shrunk sharply due to fires and lot development but were recovering. Dunes had migrated to the northeast and stabilized. Introduced species dominated the grasslands on the upper plateau. By contrast, native species continued to dominate Violet Point. Native dune grass, however, was expanding on Violet Point and tended to exclude most other species. Richness, percent cover, and diversity of introduced species on Violet Point were significantly lower than on the upper plateau, while richness and percent cover of native species were higher. Continued prevalence of native species on the point may be a result of a plant community adapted to the low, rocky substrate and frequent disturbance by nesting gulls. © 2008 by the Northwest Scientific Association. All rights reserved.

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Northwest Science





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