The biomass of European forests : an integrated assessment of forest biomass maps, field plots and national statistics

Forest biomass is a relevant source of energy and material for the European bioeconomy. The JRC Biomass Assessment Study recognized the need for an up-to-date, harmonized and spatially-explicit estimate of the biomass stock in Europe to better understand its current and future contribution to a sustainable bioeconomy. In this perspective, the present report provides an overview of existing forest biomass data in Europe, describes the methodologies used to harmonize and compare them, and proposes an improved biomass map consistent with the forest inventory data. An analysis of the existing biomass data showed that European countries employ different forest and biomass definitions and provide estimates that refer to different periods and spatial scales. It is therefore essential to perform steps to harmonize the national biomass data and existing biomass maps to perform any meaningful pan-European assessment. The biomass data provided by the National Forest Inventories (NFIs) were first harmonized among each other in terms of biomass definition thanks to a dedicated effort and collaboration of 26 European NFIs. They were then further harmonized with the biomass maps for forest definition and reference year using forest cover maps and a forest growth model within the JRC Biomass Assessment Study. The national statistics were also harmonized by the NFIs regarding the forest area and biomass available for wood supply, using the same reference definition and common criteria to assess wood availability and related restrictions. This data harmonization effort produced a reference database of forest biomass in Europe, which includes statistics at sub-national scale and field plots, both harmonized for biomass pool and reference year. The reference database was used to assess the uncertainties of publically-available biomass maps at different spatial scales. A dedicated analysis quantified the impact of the harmonization of the reference data on the maps validation, highlighting the essential role of the harmonization procedure to obtain reliable results. The validation exercise indicated that, overall, the biomass maps have relatively low accuracy for Europe, especially at local scale, and suggested the need for an improved product. Thus, the map with the highest accuracy was further improved applying a bias-removal approach, where the reference data were used to quantify and remove the systematic difference of the map with the harmonized statistics. The result is a biomass map of Europe at 1 ha resolution for the year 2010 in line with the reference statistics in terms of forest area and biomass stock. The harmonized biomass map along with the harmonized statistics on biomass stock and biomass available for wood supply support an improved estimation of the current and potential supply of biomass resources from European forests as well as their availability and cost, towards a better assessment and modelling of the role of forest biomass in the European bioeconomy. Lastly, this study provides an overview of the current status and the upcoming developments in the field of satellite, airborne and terrestrial remote sensing of forest biomass. As these new technologies are rapidly maturing and becoming operational, they open the possibility for an integrated monitoring system that allows the detailed, frequent and accurate estimate of the forest resources.