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

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. 1 Author to whom correspondence should be addressed. E-mail: [email protected] Introduction Protection Island National Wildlife Refuge, Washington State, contains one of the largest marine bird and mammal breeding sites in the Pacific Northwest. The island plays a crucial role in a coastal ecosystem experiencing intensifying human population pressures in one of the fastest growing regions of the United States. Despite its biological significance, little study has been given to Protection Island’s topography or vegetation. Exceptions include a brief unpublished overview of the island’s Pleistocene geological features (Carson 1983), unpublished results of an August 1983 vegetation survey (Washington Natural Heritage Program 1983), and memoirs by former residents. Protection Island (Figure 1) is a 1.4 km (136 ha) crescent-shaped landmass in the southeast corner of the Strait of Juan de Fuca. The island contains an undulating upland plateau surrounded by steep bluffs and is flanked on the east and west by two gravelly points. The upland plateau has an area of 1.2 km (115 ha) and varies in elevation from 35-62 m. About 75% of the plateau is covered by grassland and 25% by forest. Strong ocean currents run along the island’s north edge and high tides sometimes rise to the base of the bluff, triggering slumping. Longshore currents carry the loose sediments to Violet Point (19 ha) on the east end and to Kanem Point (1.9 ha) on the southwest end. Except for a brackish marsh which was located at the west end of Violet Point before development (Figure 1A), the island has no stable freshwater supply, and Native Americans apparently never permanently inhabited the island (Power 1976). We use data from historical records, aerial photos, GIS analysis, and vegetation transects to identify changes in Protection Island’s topography over the past century and a half. We also discuss how human disturbance and natural processes have altered vegetation assemblages on the island.