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 (Corpus 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.

The mechanisms linking spring flooding to changes in plant primary production were examined in seasonally flooded shallow prairie marshes dominated by whitetop (Scolochloa festucacea) at Delta, Manitoba, Canada. This study tested the hypotheses that flooding influences aboveground production by: (1) altering biomass allocation between above- and belowground structures, (2) changing soil salinity, and (3) by changing availability of plant-limiting nitrogen. Experimentally manipulated water levels provided comparisons between marshes with spring flooded and nonflooded hydrologic regimes. Spring flooding increased aboveground production (950 g/m$\sp2)$ compared with nonflooded marsh (360 g/m$\sp2).$ Flooding increased the number of flowering shoots and mid-summer shoot recruitment. Ingrowth mesh bag methods for estimating belowground production showed consistently greater estimates and lower sampling variability compared with soil coring methods. Below ground production measured by mesh bags was greater in flooded marsh (415 g/m$\sp2)$ than in nonflooded marsh (309 g/m$\sp2).$ Changes in total production between flooding regimes indicated that differences in aboveground production could not be explained solely by changes in biomass allocation. Flooding reduced pore water salinity compared with nonflooded marsh but mean growing season soil salinities at 15-cm depth over two years in both flooded marsh (12 mS/cm) and nonflooded marsh (17 mS/cm) were greater than the salinities (approximately 8 mS/cm) that reduced whitetop growth by more than 50 percent in greenhouse trails. Irrigation of plots with fresh water in nonflooded marsh reduced pore water salinity and increased whitetop growth. Flooding appeared to increase whitetop growth by providing plants access to fresh water in the top 10 cm of the soil profile. Net nitrogen mineralization rates were greater in flooded marsh (261 kg N/ha/y) than nonflooded marsh (114 kg N/ha/y). Net nitrification was significant in nonflooded marsh (60 kg N/ha/y) but not in flooded marsh ($<$1 kg N/h/y). Net nitrification increased levels of soil nitrate during summer and early spring in nonflooded marsh. Net mineralization rates in flooded and nonflooded marsh approximately balanced whitetop nitrogen uptake requirements. However, irrigation of nonflooded marsh did not increase net mineralization rates while increasing whitetop growth, indicating that soil salinity and not nitrogen availability provided the most immediate control over plant growth.