Modelling the dynamics of the forest ecosystem for climate change studies in the boreal conditions

This paper summarizes a forest ecosystem model developed for assessing the effects of climate change on the functioning and structure of boreal coniferous forests under the assumption that temperature and precipitation are the basic dimensions of the niche occupied by any one tree species. Special attention is paid to specifying weather patterns to a level representing the time constant of different physiological and ecological processes relevant to the regeneration, growth and death of trees. The long-term dynamics of the forest ecosystem have been coupled with climatic factors at the level of mechanisms, e.g., photosynthesis and respiration, in terms of the energy flow through the ecosystem. Furthermore, hydrological and nutrient cycles couple the dynamics of the forest ecosystem with climate change through soil processes representing the thermal and hydraulic properties of the soil and the decomposition of litter and humus with the mineralization of nutrients. Simulations for southern Finland (62 degrees N) and northern Finland (66 degrees N) indicated that a transient increase in temperature by 4 degrees C over a period of 100 years could substantially increase soil temperature and reduce soil moisture in forest ecosystems dominated by Scots pine. At the same time, the temperature increase could enhance photosynthetic production and consequent stemwood growth in southern Finland by about 8% and in northern Finland by about 19%. Given the current temperature but elevating CO2 concentration, the increase in photosynthesis in southern Finland could be about 23% and in northern Finland about 21%, but the concurrent elevation in temperature and CO2 concentration increased photosynthesis by about 32% in southern Finland and by about 40% in northern Finland. Transpiration decreased by as much as 10-20% under the changing climate with the consequence that water-use efficiency increased by as much as 25-45%, the higher values representing southern Finland. (C) 1997 Elsevier Science B.V.