EFFECTS OF SOIL DISTURBANCE ON VEGETATION RECOVERY AND NUTRIENT ACCUMULATION FOLLOWING WHOLE-TREE HARVEST OF A NORTHERN HARDWOOD ECOSYSTEM

1. Accumulation of recovering vegetation is often the principal mechan ism limiting nutrient loss following large-scale disturbance of forest ecosystems. The relationships were examined between soil disturbance associated with whole-tree harvest, and the rates and patterns of biom ass and nutrient accumulation in regrowing vegetation at Hubbard Brook Experimental Forest (HBEF), New Hampshire. 2. Recovering vegetation w as dominated initially by pin cherry and Rubus spp., but the importanc e of the tree species that dominate the mature forest (beech, maple, b irch) increased through 6 years of succession. In general, vegetation recovery was comparable to that following previous clearcutting experi ments at HBEF. 3. Very high spatial variation was observed in the comp osition and density of the recovering vegetation. The principal causes of this variation were disturbance to the soil during the harvest ope ration and availability of reproductive propagules. 4. Significant dif ferences in composition and growth of the plant community were observe d among three soil disturbance classes. On severely disturbed sites, w here mineral soil was exposed, pre-existing seedings were mostly elimi nated and early rates of biomass and nutrient accumulation were low, p artly because of slow early growth of colonizing yellow birch and prob ably also partly because of low site quality (water and nutrient avail ability). Later, the root system of trees growing on severely disturbe d sites grew laterally into adjacent, more fertile locations and growt h rates increased. Scarified sites often supported very dense stands o f pin cherry that grew rapidly for a few years, but in Years 5-6 suffe red from severe intraspecific competition that apparently limited biom ass and nutrient accumulation. Within this scarified class the nature and intensity of soil disturbance were quite variable so that high wit hin-class variation in vegetation recovery was observed. The highest a verage rates of biomass and nutrient accumulation were observed on und isturbed sites, but very high spatial variability in tree density was also observed in this class. 5. Very high nutrient concentrations (esp ecially nitrogen) in pin cherry and Rubus spp. in the first 2 years re sulted in non-linear relationships between biomass and nutrient accumu lation in vegetation across sites and years. Also, relatively low calc ium concentrations in the wood and bark of pin cherry led to relativel y low rates of calcium accumulation in vegetation.