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Yellow Bush Lupine Invasion in Northern California Coastal Dunes II. Mechanical Restoration Techniques

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Abstract

Invasion of coastal dunes by Lupinus arboreus (yellow bush lupine) results in soil enrichment and displacement of native plants. Restoration by means of heavy equipment was tested as an alternative to costly manual techniques in a heavily invaded area of relatively flat terrain. Two experiments were conducted in consecutive years at the Eureka Dunes Protected Area in Humboldt County, California. Each experiment consisted of three plots subjected to one of three primary treatments: removal of vegetation with a brush rake, removal of vegetation with a brush rake followed by removal of litter and duff with a plough blade or bucket, and removal of vegetation with tractor-pulled chokers. Plots were then subdivided into smaller secondary treatment plots subjected to one of two treatments or a control. Secondary treatments consisted of weedmat placed for a 1- or 2-year duration. The goal of the treatments was to remove and prevent reestablishment of nonnative vegetation, including but not limited to bush lupine; success was measured by percent cover of recolonizing vegetation 1.5 years after treatment ended. In the first experiment, primary treatment (vegetation removal) but not secondary (prevention of reestablishment) resulted in significant differences in cover by the end of the experiment. The brush rake and plough blade treatment was most successful at preventing reestablishment of nonnative vegetation. In the second experiment, secondary treatment (prevention of reestablishment) but not primary (removal of vegetation) resulted in significant differences at the end of the experiment. Re-invasion increased with the amount of time subplots were left uncovered. The difference in the results of the first and second experiments was attributed to variation in rainfall and, to a lesser extent, to localized variation in species composition. Results suggest that mechanical restoration by means of combination of the brush rake and plough blade primary treatment with the 2-year weedmat secondary treatment would be most successful in meeting the dual goals of removal of nonnative vegetation and prevention of its reestablishment.

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