Exotic plant inventories in Mount Rainier, North Cascades, and Olympic National Parks

Rochefort, Regina; Bivin, Mignonne; Conquest, Loveday; Acker, Steven; Kurth, Laurie

Non-native or exotic plant species threaten the integrity of natural ecosystems and pose a significant threat to the unique and rare botanical resources that we aspire to protect in national parks of the North Coast and Cascades Network (NCCN. In 2001 and 2002, exotic plant inventories were conducted in Mount Rainier (MORA), North Cascades (NOCA), and Olympic (OLYM) national parks. The objectives of our study were to: 1) document exotic plant species that occur in vulnerable habitats in each park, 2) describe distribution patterns of exotic plant species across vulnerable habitats, 3) identify habitats with the greatest exotic species richness, 4) identify patterns of exotic species richness with respect to elevation and distance from trailhead, and 5) identify priority (invasive) exotic species for control based on biological and management considerations. Susceptible habitats were defined as areas where soils and/or substrate are frequently disturbed, providing an opportunity for exotic species establishment. The four susceptible habitats surveyed for this report were: riparian areas, roadsides, trail corridors, and developed zones. We surveyed 697 plots across the three parks and documented 112 exotic species in 348 (~50%) of the plots. We documented 42 exotic species in MORA, 64 at NOCA, and 81 in OLYM. At all three parks, exotic species richness was generally highest in plots located in roadsides or developed zones. Our study documented 8 species that were not on the parks’ comprehensive online species lists (NP Species 2016): 2 at MORA and 6 at OLYM. Although we did not document any new species at NOCA, our study provided previously unavailable abundance information for that park. We found that habitat (P=0.00000), canopy cover (P=0.0000444), and vegetation type (P=0.00000) were all statistically significantly associated with exotic percent cover. Slope, aspect, elevation, distance from trail, disturbance level, and location were not statistically significantly related to exotic percent cover. Exotic plant percent cover was higher in developed zones and roads than along trails or in riparian zones. Canopy cover was inversely related to percent cover and there was a significant influence of dominant vegetation type on exotic plant abundance. We recommend that our survey be repeated, but expanded to include undisturbed areas along transportation corridors and developed zones where shade tolerant introduced species may thrive.

Exotic plant inventories in Mount Rainier, North Cascades, and Olympic National Parks

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