ALBERT

Description: A major ice storm in January 1998 provided an opportunity to study the effects of a rare, intense disturbance on the structure of the northern hardwood forest canopy. Canopy damage was assessed using visual damage classes within watersheds of different ages at the Hubbard Brook Experimental Forest (HBEF) and changes in leaf area index in two of these watersheds. Ice thickness was measured, and ice loads of trees were estimated using regression equations. In the 60- to 120-year-old forests (mean basal area 26 m2·ha1), damage was greatest in trees 〉30 cm diameter at breast height and at elevations above 600 m. Of the dominant tree species, beech (Fagus grandifolia Ehrh.) was the most damaged, sugar maple (Acer saccharum Marsh.) was the most resistant, and yellow birch (Betula alleghaniensis Britt.) was intermediate. Trees with advanced beech bark disease experienced heavier ice damage. Little damage occurred in the 14-year-old forest, while the 24- to 28-year-old forest experienced intense damage. In the young stands of this forest, damage was greatest between 600 and 750 m, in trees on steep slopes and near streams, and among pin cherry (Prunus pensylvanica L.). Recovery of the canopy was tracked over three growing seasons, and root growth was monitored 1 year after the storm. Because of the high density of advance regeneration from beech bark disease and root sprouting potential in ice-damaged beech, HBEF will likely see an increase in beech abundance in older forests as a result of the storm. There will also be a more rapid change from pioneer species to mature northern hardwoods in the younger forests. These predictions illustrate the ability of rare disturbances to increase heterogeneity of forest structure and composition in this ecosystem, especially through interactions with other disturbances.

Description: To investigate the mechanisms of indirect effects of the increased presence of American beech (Fagus grandifolia Ehrh.) saplings on sugar maple (Acer saccharum Marsh.) seedling survival, I conducted several experiments in the area of the Hubbard Brook Experimental Forest in central New Hampshire, U.S.A. To investigate the effects of competition from beech saplings on sugar maple seedlings, a removal experiment was conducted. Sugar maple seedling survival was monitored in five replicate plots of each of the two treatments for 6 years. Survivorship in plots in which beech saplings had been removed was significantly higher (33%) than in control plots (1%). A shading experiment demonstrated that a large proportion of the mortality of sugar maple seedlings results from the effects of shading. Cutting and shade cloth treatments were done in a two-factor factorial block design, and results showed a strong negative effect of shading in the plot. A third experiment investigated the role of soil moisture. Plots that had higher soil moisture and also had beech removed had the highest survival (76%), while control plots in a dry area had the lowest (22%). Overall, the experiments showed that beech bark disease and the associated increase in beech saplings had a negative indirect effect on sugar maple seedling survival. Sugar maple regeneration failure appeared to be, at least in part, due to the indirect effects of beech bark disease.

Description: In an effort to reexamine the factors that affect codominance of American beech (Fagus grandifolia Ehrh.) and sugar maple (Acer saccharum Marsh.), a greenhouse experiment was conducted to test the potential phytotoxic effects of American beech leaf leachate on sugar maple seedlings. We utilized an experimental protocol that addressed phytotoxic, nutrient, and pH effects by watering seedlings with seven treatment solutions: simulated throughfall water, average and dilute concentrations of beech leachate, average and dilute concentrations of maple leachate, and average and dilute concentrations of nutrient solutions. Sugar maple leachate had no effect on sugar maple seedling development, chemistry, or physiology. However, sugar maple seedlings exposed to average levels of beech leachate had significantly lower leaf area, fewer nodes, lower biomass, higher carbon assimilation rates, and higher stomatal conductance than seedlings exposed to the control solution. Results suggest that secondary compounds in beech leaf leachate are suppressing sugar maple seedling development and that field experiments are needed to explore the potential allelopathic relationship between these species.