讲座简介：

Contrary to earlier expectations of increased forest growth under rising temperature and atmospheric CO2 in boreal forests, growth in many Nordic forests has declined in recent years. Due to the potentially vast negative consequences for both the economy, ecology, and carbon sequestration, a better understanding of the reasons for this decline is urgently needed. Several environmental factors limit tree growth, including temperature, CO2, soil moisture, humidity of the air, and soil nutrient availability. But although the separate effects of water limitation and soil nitrogen availability are well known, it remains a challenge to predict how trees manage their combined effects under novel conditions. To address this question, we introduce a new physiological model based on optimality principles which accounts for plasticity in stomatal conductance and leaf nitrogen concentration. This allows the model not only to capture gross primary productivity (GPP) and transpiration in response to weather conditions but also effects of soil moisture and nitrogen availability. We demonstrate the accuracy of the model compared to GPP estimates from eddy flux measurements and canopy transpiration in fertilized and unfertilized pine forest in northern Sweden. We also show that the response to increased soil nitrogen availability can be captured by a reduced carbon cost of N uptake and an increased leaf area per sapwood area. The results imply that the interactive effects of water and N limitation on GPP and water use in boreal pine forest can be explained by the trees striving for an optimal balance of maximizing growth while limiting hydraulic risk. This model provides a fundamental tool for analyzing the expected future growth of Nordic forests and potential management strategies.

主讲人简介：

Oskar Franklin joined the former IIASA Forestry Program in June 2004, where he developed large-scale models for the prediction of forest production in response to management options. He is currently associated with the Agriculture, Forestry, and Ecosystem Services Research Group of the Biodiversity and Natural Resources (BNR) Program. Recently, he worked on ecosystem theory and models of boreal forests as well as wildlife management under climate change. He also led an international working group on the development of a new generation of vegetation models that takes advantage of ecological and evolutionary principles to better constrain the predicted consequences of climate change.

Franklin received his PhD in systems ecology at the Swedish University of Agricultural Sciences in Uppsala in 2003. His work involved optimal plant theory and forest growth responses to nitrogen and carbon dioxide. Prior to becoming involved in ecology, he earned an MSc degree in physics engineering at Uppsala University, and worked at the Swedish Radiation Protection Institute with nuclear power emissions and environmental effects.