JULIE A. RICHBURG- UMASS
In the Northeast, land managers are combating the deleterious effects that invasive plants have on other species and natural communities with attempts to remove them or substantially reduce their density. Control methods vary depending on the target species’ growth form, the extent of the invasion, and other species and resources at the site. Mechanical treatment, prescribed fire, hand-pulling, and application of herbicides, alone or in combination, have all been used to attempt control.
Woody invasive plants are often difficult to eliminate due to their ability to sprout from stems, stumps, and roots. Successful control of these species requires understanding temporal variations in their below-ground resources. Total non-structural carbohydrate (TNC) reserves in the roots of woody species support growth following disturbance and generally follow an annual cycle of depletion and replenishment. This study evaluates the effectiveness of treatments when applied during periods of decreased TNC reserves.
Treatments were applied to seven invasive shrubs (Cornus racemosa, Rhamnus cathartica, Rosa multiflora, Berberis thunbergii, Lonicera morrowii, Smilax rotundifolia, and Cytisus scoparius) at three different sites in Massachusetts and New York. Treatments included cutting and/or burning, applied singly or in combination, in either the dormant or growing seasons.
TNC were depleted following all treatments. Dormant-season-treated plants, whether cut or burned, sprouted and replenished their reserves within the following growing season. For growing-season-treated plants TNC remained depleted longer, with a greater effect on plants that received more treatments. For most species studied, TNC recovered to pre-treatment levels by the end of one growing season without treatment.
Sprout growth was influenced by the extent of carbohydrate reserves present before treatment. Biomass and heights of sprouts were significantly lower in growing- season-treated plants than those treated in the dormant season, even when data were adjusted for different lengths of recovery time.
All treatments reduced the cover of the target invasive shrub. As the plants sprouted, they regained some of their initial cover and are expected to dominate without further treatment. Timing treatments to the cycle of TNC can increase the effectiveness of control methods, although repeated treatments may be necessary for several years.