Spruce decline as a disturbance event in the subalpine forests of the northeastern United States

Abstract

During the last 2 decades red spruce (Picearubens Sarg.) trees have died at high rates in the mountains of New York and New England. Given the importance of disturbance in organizing plant communities, the impact of the decline was evaluated in terms of its effect on disturbance processes. The first step was to describe the current disturbance regime in subalpine forests across the region. Canopy gaps were the predominant mode of disturbance. Estimates of gap-phase disturbance in four old-growth sites ranged from 15% to 42% of the total forested area. Gap abundance varied between 19 and 49 gaps/ha. A constant among the sites was that dead spruce trees accounted for more of the gap area than expected considering their abundance in the canopy. In the spruce–fir forest, most gaps were small (<100 m2). Gaps were not shaped like simple geometric figures but rather like irregular polygons. Forty percent of the canopy gaps were created by the death of a single tree; the rest were multitree gaps. Standing dead trees were the most common damage type. It seems that decline of spruce effected a quantitative but not qualitative shift in the disturbance regime.