Abronia umbellata ssp. breviflora on the Oregon coast: Reintroduction and population monitoring

EXECUTIVE SUMMARY
Pink sand-verbena (Abronia umbellata ssp. breviflora) is listed as endangered by the Oregon Department of Agriculture, and a Species of Concern by the U.S. Fish and Wildlife Service. Since the late 1970’s, the number of natural populations in Oregon has decreased by approxiamately 50% (~10 to ~5). The primary threats to the species include competition from European beachgrass (Ammophila arenaria) and other weedy beach species, and other human-influenced habitat changes.
This report includes information about pink sand-verbena research along the Oregon coast since 1997, including seeding and transplantation experiments, and population monitoring at several beach and dune habitats.
In 2016 our actions and observations included activities at the sites listed below:
1. USDA Forest Service, Siuslaw National Forest sites
a. Tahkenitch: ~80,000 seeds were distributed at Tahkenitch in 2016, resulting in a total of 141 plants (76 reproductive). This was the sixth seeding at the site since 2005. In 2014-2016, seeding was focused in the southern 1/3 of the site, as this was the area that had been most successful in previous years.
b. Siltcoos Creek: ~53,000 seeds were distributed in the habitat still present at the site and 427 plants (330 reproductive) were found in the fall of 2016. Natural disturbance at the site in 2011 resulted in the erosion of more than 80% of the area occupied by A. umbellata ssp. breviflora in the 2010-11 growing season. Despite the significant loss of habitat several plants were present in 2012-2015, and in 2016 the site had rebounded to 427 plants (330 reproductive). Continued seeding is recommended for the site to maintain a seedbank as the habitat re-establishes.
c. Overlook: Despite substantial decreases in this population in 2014 and again in 2015, this population is now the second largest in Oregon and we strongly recommend continued beachgrass control and seed addition. In 2016, both Overlook sites increased from 2015 numbers; however remained relatively low for the history of the site.
i. North: ~63,000 seeds were distributed, resulting in 269 plants (158 reproductive)
ii. South: ~60,000 seeds were distributed resulting in 614 plants (375 reproductive).
2. USDI Bureau of Land Management, Coos Bay District sites
a. New River: ~100,000 seeds were distributed by BLM staff, resulting in just 108 plants (30 reproductive). This represents a substantial decrease from previous years, particularly 2015. In 2016, as in previous years (2012-2015), most plants were found in areas where breaks in the foredune had allowed overwash to occur– highlighting the affinity of pink sand-verbena for areas with repeated disturbance (and possibly nutrient input). Continued seeding at the site to augment the existing seed bank, and management in the form of continued European beachgrass control, as well as control of other non-native species including Hypochaeris radicata, Cakile maritima, and Rumex acetosella, will be vital in maintaining suitable coastal dune habitat for this and other dune species.
b. Coos Bay North Spit: ~100,000 seeds were distributed by BLM staff. In 2016, it is estimated that there are approximately 306,000 pink sand-verbena plants on the Coos Bay North Spit. Over the course of this study, we have seen an increase in the number and diversity of weed species at this site. This is likely due to soil formation related to sand stabilization and the lack of overwash and salt-spray in the area that contribute to natural soil formation processes on this coastal dune. Without natural disturbance on the site, management to reduce beachgrass includes discing at least annually. There was a precipitous drop in the population when beach grass management was discontinued for just one year in 2013 in the southern portion of the population; this portion of the population rebounded when discing resumed in 2014-2016.