Assessing performance of a “nature‐based” foredune restoration project, Oceano Dunes, California, USA

Abstract

AbstractThe Oceano Dunes near Pismo Beach, California is part of a large transgressive dune system that extends up to 5 km inland and hosts a state park that has been managed for off‐highway vehicle recreation since 1982, although vehicle activity has existed in the dunes for almost 90 years. As a result, foredunes have been largely obliterated and sand surfaces in vehicle use areas are highly emissive of dust‐sized particles, causing frequent exceedances of state air quality standards. To reduce dust emissions from the dunes, a nature‐based foredune restoration strategy using five different treatments over a 20‐ha site was implemented in February 2020.The research hypothesis is that treatments will differ in their ability to promote deposition and dune development and that more intensive planting‐based treatments will outperform simpler treatments. We test this using biannual high‐resolution uncrewed aerial system (UAS) surveys to quantify sediment budgets, sand exchanges between beach, foredune, and backdune components, changes in plant cover, and related dune development over a 2‐year period (October 2019–2021). After two full wind and plant‐growth seasons, results show that all treatments are maintaining a positive sediment budget (net accumulation), most are developing sizable nebkha dunes (an important stage in foredune development in this region), and some are increasing plant cover and species richness. There is no clear winner, yet two treatments (broadcast native plant and sterile grass seeds, and a high‐density straw planting node with native seedlings) are performing well toward developing an incipient foredune.These results will inform an adaptive management process that could entail further modifications to enhance foredune development. Based on this experience, and with reference to other types of restoration projects, we refine existing criteria used to assess the performance of “dynamic” dune restoration efforts to include settings that involve revegetation (vs. devegetation) as a means for foredune re‐establishment.