Evaluation of the response of a spruce forest ecosystem on climatic changes: Results of modelling experiments

The physical and chemical environment of forests will change in the future. How forests will react to new conditions is not known yet. In order to get an idea of the sensitivity of present forests to possible atmospheric chan ges, it is helpful to investigate the physiological response of forest ecos ystem to a change of key environmental parameters. In order to estimate the response of a mountain spruce forest to different atmospheric conditions during the summer a six-layer non-steady-state SVAT model (SLODSVAT) was used Eight scenarios were used for modelling energy an d mass exchange during an eleven day summer period, combining different com binations of microclimatic conditions. All atmospheric scenarios were exami ned for three various CO2 mixing ratio levels: 350ppm (current condition), 450ppm and 550ppm. A scenario "0" assuming the current climatic features at different CO2 contents was considered as well. Structural and physiologica l adaptation of the forest to the new atmospheric conditions were not taken into account. For all scenarios the modelling results show increased net C O2 flux into the forest with increasing ambient CO2 concentration. Maximum net CO2 uptake was simulated for dry climate scenarios. Transpiration and e vapotranspiration rates had similar trends independently of the ambient CO2 concentration used: at cold and wet conditions they decreased, while at wa rm and dry conditions transpiration and evapotranspiration rates increased The influence of CO2 concentrations on transpiration rates is of minor impo rtance if compared to changes of temperature, water vapour pressure, cloud amount and atmospheric precipitation as considered in this investigation. ( C) 1998 Elsevier Science Ltd. All rights reserved.