Dune Restoration Over Two Decades at the Lanphere and Ma-le’l Dunes in Northern California

Abstract

Coastal dune restoration on the west coast of North America has focused on the removal of invasive plants that reduce biodiversity and/or alter ecosystem processes. Manual removal (digging) of Ammophila arenaria and other non-native plants was carried out from 1992 to 1998 at the Lanphere Dunes, and from 2005 to 2010 at the Ma-le’l Dunes, both currently part of Humboldt Bay National Wildlife Refuge. The earlier project removed Ammophila over several years in a patchwork fashion to avoid mobilizing dunes. Over the ensuing two decades vegetation recovered without assistance and is now similar in cover and species composition to nearby uninvaded dunes. In contrast, Ammophila removal at the Ma-le’l Dunes was not spatially phased, and increased foredune erosion was observed. The native dune grass Leymus mollis was planted and continues to spread. Vegetation at the Ma-le’l Dunes, representing an earlier point along the temporal restoration continuum, is currently lower in cover than the Lanphere restoration and lower in species diversity than both the earlier restoration project and the uninvaded dunes. Manual removal was costly, but reduced or eliminated the need for revegetation. Community volunteers were engaged and continue to support both projects, improving the long-term outlook for preventing reinvasion.