Restoration of spotted knapweed infested grasslands in Glacier National Park

Abstract

There is an immediate and on-going need in Glacier National Park (GNP), and other public and private lands, to determine effective methods to re-establish and sustain native plant populations following control treatments of Centaurea maculosa. My research was developed in response to GNP concerns regarding annual herbicide treatment of C. maculosa invaded sites. The aim of this study was to determine if herbicide applications, site preparation and revegetation methods would increase the density and percent cover of native species, while reducing spotted knapweed at two sites in and near Glacier National Park. A priori contrast analysis was used to determine differences in treatment effects. The results of my experiment show that spot spray herbicide application reduced C. maculosa cover without significantly reducing existing native forbs. However, a repeat-herbicide application increased exotic graminoid cover. Tillage reduced the density of C. maculosa seedlings, but resulted in an increase in C. maculosa percent cover, and an overall decline in native forbs. Revegetation methods had limited success at increasing native species, and reducing C. maculosa. The only effect was at Swift Current, where the percent cover of native forbs was significantly higher with the planting treatment, and most pronounced in plots with repeat-herbicide application. Additionally, we measured the composition and density of the seed bank in C. maculosa dominated sites using the seedling emergence method. C. maculosa density was 3,900 and 6,714 seeds / m 2 at the two sites, which was 2 and 3 times higher than the sum of all other species. Seed bank composition and density needs to be considered in efforts to restore C. maculosa infested areas.