Mounding as a Technique for Restoration of Prairie on a Capped Landfill in the Puget Sound Lowlands

摘要

Closed landfills create large open spaces that are often proposed as sites for restored or created ecosystems. Grasslands are probably prescribed most often because of the presumption that grass root systems will not breach the landfill cap. Capped landfills have a number of soil degradation problems, including compaction, decreased permeability, lack of organic material, diminished soil fauna, inappropriate texture, and lack of structure. In this study in the Puget Sound lowlands, Washington, U.S.A., mounding (low sandy-loam mounds, about 20 cm high and 2 m in diameter), addition of fertilizer, and mulching with yard-waste compost were applied to landfill sites as treatments in a factorial-design experiment. Prairie plants (1,344 individuals, 7 species) were planted into 4-m2 plots (n = 48), and plant growth and survival and the increase in weed biomass were monitored for 3 years. Mulching had no effect on plant survival or growth. Fertilization had a negative effect on Lupinus lepidus, a nitrogen-fixing species. Mounding had a positive effect on growth and survival of Eriophyllum lanatum, Festuca idahoensis, and Aster curtus. Potentilla pacifica was indifferent to mounding, and Carex inops responded negatively. Mounds should probably be used as one element of a complex of habitats on restored landfills.