Interactions between land-use history, nitrogen cycling, and beech bark disease in northern hardwood forests

A study was conducted to examine the structural and functional characteristics of old-growth and previously disturbed forests in response to an introduced pathogen and elevated nitrogen deposition. Few compositional and structural differences were observed between old-growth forests in the Adirondacks, New York and nearby forests that were selectively logged 80--100 years earlier. In northern Maine, the smaller basal area of second-growth relative to old-growth stands indicated that forest structure had not recovered from logging that took place 60--80 years ago. In both regions red spruce (Picea rubens Sarg.) was more abundant in old-growth, a legacy of red spruce harvesting. Over 20 years, within Adirondack old-growth forests, more significant changes in species composition occurred. Data collected in 1995 compared with a survey of the same region from 1975 indicated that populations of red spruce and American beech (Fagus grandifolia, Ehrh.) had declined.; Functional comparisons between old-growth, logged, and logged then burned forests demonstrated that disturbance history can have lasting effects on soil carbon and nitrogen pools. Carbon and total nitrogen concentrations were highest in old-growth and lowest in burned forests. Other soil properties including pH, the percentage of soil organic matter, base cation content, phosphorous content, net nitrogen mineralization, and nitrification rates were statistically equivalent among forests with contrasting histories. Despite the similar nitrogen mineralization rates, beech trees from old-growth had significantly higher nitrogen concentrations in their bark and leaves than did similarly sized trees in previously logged stands.; In the Adirondacks, old-growth forests contained more beech trees acutely infected with beech bark disease relative to second-growth forests, Disease symptoms were positively correlated with nitrogen concentrations in beech bark. These data suggest that old-growth forests in this region are becoming nitrogen saturated resulting in higher concentrations of nitrogen in plant tissues. In response to the higher quality bark of old-growth trees, the fitness of the phloem feeding insect initiator of beech bark disease (Cryptococcus fagisuga Baer.) is increased causing more severe infestation in old-growth forests. This research indicated that novel anthropogenic disturbances, like nitrogen saturation and introduced pests, are likely to have greater effects on future forest dynamics than modest logging.