A FOREST SOIL VEGETATION ATMOSPHERE MODEL (FORSVA) .2. APPLICATION TONORTHERN TOLERANT HARDWOODS

The ForSVA (forest soil-vegetation-atmosphere) model of the preceding paper was used for simulating biomass growth and nutrient cycling (Ca, Mg, K, N, S) in three northern tolerant hardwood sites in eastern Nor th-America: one north of Lake Superior (Turkey Lakes site), one in the Harp Lake watershed near Dorset, Ontario, and one in the Adirondack M ountains of New York State (Huntington Forest). The basic model calibr ation was done for the Turkey Lakes site. Model performance testing, a s well as testing the general portability of the model formulation bey ond that which is valid for the initial calibration site, was done wit h the other two sites, Model simulations included the evaluation of bi omass and nutrient contents of all major stand compartments (foliage, fine roots, wood including bark and coarse roots, forest floor, ion ex change complex, soil solution, soil matrix within the rooting zone) ov er several tree life cycles, or stand cycles. Also addressed were carb on and nutrient flows into and out of these compartments in conjunctio n with the potential impacts of acidifying atmospheric ion deposition (SO42-, NO3-, NH4+, H+). It was found that current atmospheric deposit ion rates of soil acidifying ions should increase the leaching of nutr ient base cations (Ca2+, Mg2+, K+) from each of the 3 sites. The corre sponding decrease in base cation availability should also lead to a de crease in soil pH, a decrease in base cation uptake, a decrease in fol iar base cation concentrations, and a decrease in biomass growth. The latter would occur once the base cation availability, as calculated, b ecomes growth limiting. Altogether, stand-level biomass productivity w as calculated to decrease under current acid sulphate/nitrate loads, a nd this decrease reduced the calculated longevity of the trees within the stands, The decrease in productivity under current atmospheric dep osition rates would be the highest at the Harp Lake site (site of high SO42- deposition with low number of cation exchange sites in the soil ) and the lowest at the Huntington Forest site (site of low SO42- depo sition). Major uncertainties in this modelling effort relate to (1) ac tual relationships between foliar nutrient concentrations and nutrient availability, (2) the influence of foliar nutrient concentrations on productivity, (3) the rate of base cation replenishment on the cation exchange sites in soils. (C) 1997 Elsevier Science B.V.