Dynamics of carbon and nitrogen fluxes and pools in forest ecosystem

Abstract

Metabolism of trees, ground vegetation and microbes generate carbon and nitrogen fluxes in forest ecosystems. Carbon flows through the system, and nitrogen circulates between vegetation and soil. Trees synthesise sugars in photosynthesis and take nitrogen from soil. The biochemical regulation system allocates the annual amounts of synthesised sugars and nitrogen taken up to the growth of needles, wood and fine roots. The regularities in tree structure, generated by the action of the biochemical regulation system, determine the allocation to different tree components. The ecosystem model MicroForest is based on the theoretical ideas outlined above. It calculates the annual amounts of photosynthesised sugars and the annual nitrogen taken up. The allocation to needles, wood and fine roots is obtained as solution of carbon and nitrogen balance equations. In addition, several rather technical assumptions are needed to describe height growth, stem base enlargement, etc. SMEAR II and I measuring stations provide data for determination of the values of the parameters. MicroForest is able to predict successfully tree growth in six stands near SMEAR II in Finland and in five stands in Estonia.