Does the establishment of broadcast milkweed seeds versus containerized plugs differ in Willamette Valley restoration plots?

Abstract

Monarch butterflies (Danaus plexippus plexippus) have been petitioned for conservation through listing under the Endangered Species Act. In the Willamette Valley, showy milkweed (Asclepias speciosa) acts as monarch natal and feeding ground habitat. Today, restoration ecologists are including showy milkweed in the suite of species used in prairie restoration projects to bolster the dwindling monarch populations. These biologists often started with including it as a portion of the seed mixes sown as part of a restoration. Later, many of these biologists switched to planting started, containerized plants (plugs) after failing to see much in the way of results from the previous seeding. This study focused on the establishment rate of containerized plugs versus broadcast seeding in restoration plots. Three prairie restoration sites were selected which had been seeded, then planted with plots of containerized plugs. Stems were counted at each site, both within the plug area, and at random across the rest of the site. Results from 2017 indicated planting plugs was more successful than broadcast seeding. However, the random sampling returned no plants and insufficient study design required a reexamination of the study sites in Summer 2018. My science advisor also recommended using the Focused (Intuitive Controlled) Survey method to collect sown milkweed instead to see if the results were different. The 2018 sampling yielded several individuals or clusters of milkweed in the sown sections. These were productive enough that we question which whether plugging milkweed is necessary.