Comparing Restoration Treatments and Time Intervals to Determine the Success of Invasive Species Removal at Three Coastal Dune Sites in Northern California, U.S.A.

Abstract

Pickart, A.J.; Maslach, W.R.; Parsons, L.S.; Jules, E.S.; Reynolds, C.M., and Goldsmith, L.M., 2021. Comparing restoration treatments and time intervals to determine the success of invasive species removal at three coastal dune sites in Northern California, U.S.A. Journal of Coastal Research, 37(3), 557–567. Coconut Creek (Florida), ISSN 0749-0208.Dune systems worldwide have been greatly altered by the introduction and spread of invasive species. On the western coast of North America Ammophila arenaria (L.) Link is the most widely introduced species and now represents the dominant vegetation type in the region. In this study, three dune restoration projects in northern California completed between 1997 and 2011 were surveyed, all of which involved the removal of A. arenaria with the aim of increasing native plant cover and richness. Each site underwent a different restoration treatment: manual removal, herbicide application, and the use of heavy equipment to excavate and bury A. arenaria. Species composition and vegetation structure in restored and reference (i.e. uninvaded) areas were recorded at each site. Reference and restored plots differed in species composition at the herbicide-treated site and the heavy-equipment site, but not at the manually treated site. Similarly, plant species richness was similar in restored and reference plots at the manually treated site, but was greater in the reference plots at the other two sites. Vascular plant cover was similar in restored and reference plots at the manually treated site, whereas the herbicide site exhibited higher cover in restored plots and the heavy-equipment site was characterized by lower cover in restored plots. Differences were attributed to a combination of treatment type and time since restoration, with the manually treated plots best meeting goals, but also having the longest time since treatment. Short-term monitoring may fail to identify that a project is on a restoration trajectory and may lead to an inaccurate conclusion of failure to meet goals.