Thesis

Evaluating the effects of mechanical and manual removal of Ammophila arenaria within coastal dunes of Humboldt County

Ammophila arenaria was introduced to North America in 1868 for sand stabilization, and since its introduction it has invaded most of the dune ecosystems of the Pacific coast of North America. The 222 ha dune ecosystem at Gold Bluffs Beach within Prairie Creek Redwoods State Park (Humboldt County, California) has become heavily invaded by A. arenaria , and if left unmanaged this habitat was likely to become a dense monoculture of A. arenaria. My hypothesis tests the efficacy of mechanical (excavators and dozers) and manual (hand-pulling) removal methods on plant community composition and regeneration. Vegetation was characterized and monitored before, during, and after A. arenaria removal. Six 25 m² plots running parallel to the shoreline were set up within each of the different removal sites (two mechanical, two manual, two control) for a total of 36 plots. Each plot was marked with GPS and rebar and three equally-spaced transects were established with five 1m² plots along each transect. Species percent cover values within the plots were established and subsequently monitored every 3 months to quantitatively evaluate A. arenaria reestablishment and native plant recovery. Mechanical removal sites had significantly lower A. arenaria regrowth than the hand removal and the control sites when averaged over all time intervals. One year postremoval, however, A. arenaria regrowth in the hand and mechanical removal sites was not significantly different. The hand removal sites had significantly more native plant cover three months post-removal than the mechanical removal sites, but this difference no longer held at one year post-removal. Mechanical removal of A. arenaria has proven to be an effective removal technique that has not impeded native plant recovery at Gold Bluffs Beach, but as with most techniques for removing A. arenaria, properly timed follow up treatment is necessary. Documenting which removal technique is most effective at eliminating A. arenaria is imperative for the conservation management of coastal dunes and the rare species that rely on them. Ultimately, my research provides the basis to establish a conservation management protocol to effectively control one of the worst invasive plants in coastal ecosystems of the Pacific Northwest, while minimizing damage to native plant communities.

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