Empirical biomass models of understorey vegetation in boreal forests according to stand and site attributes

In the early phases of succession, the proportion of biomass comprising understorey vegetation may be considerable and, therefore, it plays a significant role in the annual nutrient and carbon cycling of forest ecosystems. The aim of our study was to identify the most significant forest-site attributes affecting the above-ground biomass of understorey vegetation and to develop models that can be used to predict this biomass in the boreal zone using readily available variables. The study was based on vegetation data consisted of percentage coverage observations collected from a network of permanent sample plots established by the National Forest Inventory in Finland. The coverage data were transformed to biomass with previously published models. According to our results, above-ground biomass can be predicted by such forest stand and site attributes as stand age and site nutrient level. In Scots pine, Norway spruce and broad-leaved forests growing on upland soil, the relative RMSE of predicted above-ground biomass of all understorey vegetation was 16.6%, 22.3% and 31.6%, respectively. In hardwood–spruce mires and paludified forests, the relative RMSE predicted above-ground biomass of all understorey vegetation was 12.2%. In pine mires it was 9.9%. The modelled relationship between biomass and forest site attributes can be used in ecosystem and carbon cycle modelling as a rapid non-destructive method to predict the above-ground biomass of understorey vegetation.