Carbon stocks in Danish forest types

Abstract: As part of international agreements, countries are now obliged to monitor their greenhouse gas emissions as well as to report their possible sources and sinks. Carbon dioxide is one of the six greenhouse gases listed in the Kyoto Protocol, contributing to global warming. Research is conducted to gain knowledge on how to maximise forest carbon storage capacity, albeit, there are some constraints and limitations to both the role of forests in CO2 mitigation efforts and the estimation and comparison of forest carbon stocks. Forests provide multiple services which might be in conflict to a management strategy solely addressing carbon storage. The estimation and comparison of forest carbon stocks is insofar limited as for instance studies use different definitions for dead wood and different soil depth. With respect to a changing climate, forests are subjected to changes that are not fully predictable yet. In this study, I have examined the effect of stand age, soil category, tree species, crown cover, broadleaf fraction, tree species biodiversity, precipitation as well as previous land use on biomass, dead wood, forest floor and soil carbon stock on Danish forests. The main influence derives from stand age, soil category, tree species and crown cover. Depending on the carbon pool one to two of these variables explain more than 50% of the variation in the respective model. In general, older forests contain more C than younger ones. With increasing age, the biomass volume grows and the forest floor develops, thus, accumulates C. Each soil category is characterized by its properties, which among others determine the turnover rate of SOM, and consequently influencing the soil C stock. The tree species significantly influence the C stocks due to their different litter quality and root system. On average, a high crown cover indicates bigger biomass volumes and hence, greater C stock. Previous land use significantly influences only the forest floor C stock. The relative C stocks are similar to the absolute ones; here the soil C pool differs most, were e.g. the effect of broadleaf fraction and biodiversity enters the model. Furthermore, other factors such as forest management and the market for forest products influence C storage. The former especially affects the dead wood, forest floor and soil C stock. The wood market in turn, influences the forest management and gives an explanation for the average age of tree species. In total, broadleaf forests and forests on organic soil category contain the most C. The average soil C stock amounts to 184 tC ha-1, the biomass C stock contains 81.2 tC ha-1 on average, about 1.16 tC ha-1 is stored in dead wood and 15.3 tC ha-1 in forest floor.