Best management practices for controlling catbrier (smilax rotundifolia), oriental bittersweet (celastrus orbiculatus), and scotch broom (cytisus scoparius) on a coastal island in Massachusetts

Polatin, Christopher C.
Peter Palmiotto, PhD
Department of Environmental Studies
The sandplain grassland communities of Naushon Island, a coastal island near Cape Cod, are being threatened by the invasion of several woody plant species including catbrier (Smilax rotunifolia), an aggressive native species, and Scotch broom (Cytisus scoparius) and oriental bittersweet (Celastrus orbiculatus), two invasive exotic species. These plants have increased as a result of changes in land management practices such as the removal of grazing animals. This study evaluated the effectiveness of mowing, spot burning, and herbicide application in controlling these three plant species and re-establishing native grasses on Naushon Island. The effects of the timing (early vs. late season) of these treatments were also evaluated. A randomized complete block design was established, treatments applied, and the percent cover of invasive plants and grasses before and after treatments were measured. Data were analyzed using nonparametric Wilcoxan/Kruskal-Wallis Signed Rank Test to determine significant differences between treatments and between timings of treatment. The late season herbicide application reduced significantly more catbrier cover than the other two treatments applied in the early or late season and the control; however, grass cover decreased in herbicide treated catbrier areas. Grass establishment was greatest in catbrier areas that were mowed. Herbicide treatments reduced bittersweet cover significantly more than other treatments or the control, with late season herbicide treatment being more effective than early season. Grass cover significantly increased in areas treated with herbicide as compared to the control; though, the timing of the herbicide treatment did not make a significant difference. Brush cutting and mowing both reduced Scotch broom cover with similar effectiveness and resulted in significant grass establishment. Although the results indicate that use of the non-selective herbicide Roundup was most effective at reducing catbrier, the elimination of all grasses makes this treatment ineffective at naturally restoring grasslands in the short-term. Mowing is likely the best technique when management goals are to control catbrier and allow for natural grassland establishment. Moving followed by application of Garlon 4, a selective herbicide, in the late season is the recommended management practice to control bittersweet and allow for natural grassland establishment. Brush cutting is the preferred method for controlling Scotch broom since this technique results in minimal soil disturbance and broom seedling regeneration in comparison with mowing. Results fro this study will be useful to both Naushon land managers and others in the coastal Northeast in implementing effective control techniques for these three invasive plants.

Read Full Text