A comparison of two modelling studies of environmental effects on forest carbon stocks across Europe

Abstract

Two modelling approaches to describing the variation in the carbon balance of forests in different parts of Europe are presented. A forest growth model (Eurobiota) was parameterised for 3 eco-climatic zones. The parameter values were derived from process-based forest growth models developed to describe the situation at forest locations within each zone. The model was separately run for conifers and broadleaves on a 30′ grid across Europe. Daily climate data covering the period from 1830 to the present and then projected to 2100 were used. European forests were shown to be a net sink of carbon of 0.06 Pg y -1 at present. The Boreal and Temperate zones are likely to continue at their present rate or more for the next century but the net sink in the Mediterranean zone may become smaller due to projected drier conditions. The effect of temperature using the surrogate of latitude on net ecosystem productivity is also discussed. A complex forest growth model (EFM) was parameterised for Norway spruce and Scots pine, and tested against measurements from 22 forest locations across Europe. This second model showed that the main driver of increased forest growth in the 20th century has been increased nitrogen deposition, rather than increased [CO2] or climate change, as indicated by EuroBiota. Increased growth has led to increased carbon storage in the system, but most of it in tree biomass rather than stably sequestered in recalcitrant soil organic matter. Carbon stocks were increased more in Central Europe than in Scandinavia, except for some high-fertility sites where N-deposition had little impact. The EFM model was also used to predict the effects of future environmental change, and suggested that climate change and [CO2] may become the dominant environmental drivers for forest carbon exchange. The two models thus give similar results when considering only climate change and [CO2] but EFM can in addition describe the effects of N-deposition when appropriate. © INRA, EDP Sciences, 2005.