NUTRIENT CYCLING AND BIOMASS GROWTH AT A NORTH-AMERICAN HARDWOOD SITEIN RELATION TO CLIMATE-CHANGE - FORSVA ASSESSMENTS

The biomass growth and nutrient cycling model 'ForSVA' (forest-soil-ve getation-atmosphere model) is used to analyze potential changes in nut rient cycling (Ca, Mg, K, N, S) and forest biomass production in respo nse to four climate-change scenarios. The analysis is done for an old growth hardwood stand within the Turkey Lakes watershed north of Lake Superior, Ontario. With ForSVA, any effects due to species interaction s, competition, and resulting species shifts are not addressed explici tly. Instead, the calculations are based on functional relationships t hat primarily respond to soil and climate conditions in general, and t o structural changes within the forest itself. The simulations cover a period of about 200 years, and suggest that a principal change in ann ual pattern of soil moisture is to be expected for the UKMO climate sc enario, and that this scenario will likely induce a major change of ve getation covertype resulting from major changes in seasonal soil moist ure conditions and a general lack of snow during winter. In contrast, the OSU, GISS and GFDL scenarios should not cause a principal change i n forest type, but the soil will be somewhat drier than what is curren tly the case. However, increased precipitation rates and/or air temper atures during summer and spring should, in combination, increase actua l evapotranspiration rates, and such increases should increase net pri mary production. For example, calculations with GFDL suggest that cumu lative wood biomass at the Turkey Lakes site can be expected to increa se by 25%. Foliage biomass and fine root production can be expected to increase by 70% from current conditions. It is assumed that within-tr ee allocation of photosynthate is not affected by climate.