Techniques to Restore Coastal Scrub at a Reclaimed Quarry in Central California

Abstract

Restoring large, drastically disturbed sites requires active techniques to create stable, self-sustaining native plant communities. We examined the effectiveness of topsoil preparation, seeding, and planting techniques for restoring coastal scrub at a 16.1 ha reclaimed quarry with steep, harsh slopes. Grading within the quarry created a benched slope spanning approximately 230 vertical meters, with a gradient of two horizontal:one vertical (2H:1V). This gentler slope was achieved by cutting the upper portion of the slope and using the cut material to fill the lower portion. Soils on cut slopes (approximately 9.0 ha) and fill slopes (approximately 7.1 ha) were prepared differently, resulting in two distinct substrates. Work crews hydroseeded native shrubs throughout the entire graded slope and installed native shrubs from container plants across half the site. Container plants were irrigated and protected from herbivory and weed competition. We conducted quantitative monitoring of woody vegetation cover for five years. We found that coastal scrub percent vegetative cover established from seed was significantly higher than that from container plantings on fill slopes amended with composted organic matter. Moreover, coastal scrub cover established from seed was significantly higher on amended fill slopes compared to cover from seed or container plants on unamended cut slopes. We conclude that coastal scrub restoration efforts on large, drastically disturbed sites should focus funds and resources on soil preparation, seed application, and site-wide invasive plant control, rather than on container plant installation and maintenance.