A MODEL FOR SIMULATING THE EFFECTS OF CHANGING CLIMATE ON THE FUNCTIONING AND STRUCTURE OF THE BOREAL FOREST ECOSYSTEM - AN APPROACH BASED ON OBJECT-ORIENTED DESIGN

We have developed a forest ecosystem model to assess the effects of climate change on the functioning and structure Of boreal coniferoUS forests assuming that temperature and precipitation are the major variables of the niche occupied by a tree species. We specified weather patterns to a level representing the time constant of different physiological and ecological processes relevant to the survival, growth and death of trees. We thereby coupled the long-term dynamics of the forest ecosystem with climate through physiological mechanisms such as photosynthesis and respiration in terms of energy flow through the ecosystem. The hydrological and nutrient cycles couple the dynamics of the forest ecosystem with climate change through soil processes, which represent the thermal and hydraulic properties of the soil, and the decomposition of litter and humus with mineralization of nutrients. Simulations for southern Finland (62-degrees-N) indicated that an increase in temperature of 5-degrees-C over one hundred years could reduce soil water in Scots pine-dominated forest ecosystems. At the same time, the temperature increase could enhance photosynthesis up to 6-8% under current CO2 concentrations (330 ppm) and up to 8-10% under elevated CO2 concentrations (660 ppm). Because the elevated temperature and CO2 concentration caused an increase in respiration (12-14% more than under the current climate), total stem production increased only up to 4% with a 5-degrees-C increase in temperature and up to 6% when temperature and atmospheric CO2 concentration were increased simultaneously. Because transpiration only increased up to 5% in response to elevated temperature and C02 Concentration, the water use efficiency of Scots-pine dominated forest ecosystems increased up to 3%, particularly during the late rotation.