YELLOW BUSH LUPINE INVASION IN NORTHERN CALIFORNIA COASTAL DUNES - II- MECHANICAL RESTORATION TECHNIQUES

Invasion of coastal dunes by Lupinus arboreus (yellow bush lupine) res ults in soil enrichment and displacement of native plants. Restoration by means of heavy equipment was tested as an alternative to costly ma nual techniques in a heavily invaded area of relatively flat terrain. Two experiments were conducted in consecutive years at the Eureka Dune s Protected Area in Humboldt County, California. Each experiment consi sted of three plots subjected to one of three primary treatments: remo val of vegetation with a brush rake, removal of vegetation with a brus h rake followed by removal of litter and duff with a plough blade or b ucket, and removal of vegetation with tractor-pulled chokers. Plots we re 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 treatment s was to remove and prevent reestablishment of nonnative vegetation, i ncluding but not limited to bush lupine; success was measured by perce nt cover of recolonizing vegetation 1.5 years after treatment ended. I n the first experiment, primary treatment (vegetation removal) but not secondary (prevention of reestablishment) resulted in significant dif ferences in cover by the end of the experiment. The brush rake and plo ugh 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 vegetatio n) resulted in significant differences at the end of the experiment. R e-invasion increased with the amount of time subplots were left uncove red. The difference in the results of the first and second experiments was attributed to variation in rainfall and, to a lesser extent, to l ocalized variation in species composition. Results suggest that mechan ical restoration by means of combination of the brush rake and plough blade primary treatment with the 2-year weedmat secondary treatment wo uld be most successful in meeting the dual goals of removal of nonnati ve vegetation and prevention of its reestablishment.