LAUSR

Abstract Forest deadwood is a key indicator for biodiversity, disturbances and for carbon storage assessments. However, the role of Mediterranean forests in deadwood carbon storage is unclear. In this regard, the European Regulation 2018/841 on the inclusion of greenhouse gas emissions and removals from land use, land use change and forestry in the 2030 climate and energy framework, requires reports by Member States on the average annual net emissions or removals of deadwood carbon. The main purpose of this work is to explore the trends of forest deadwood carbon to clarify the role of Spanish forest as deadwood carbon storage. We also investigate the effect of forest stand, climatic and physiographic variables on the deadwood carbon trends. For the purposes of our study, we used the deadwood data from two cycles of the European large-scale forest condition-monitoring programme Level I, which spanned from 2009 to 2017. Our findings indicate that there is statistical evidence of increments in deadwood carbon stocks in Spain over the last decade. We also identified certain spatial trends of mean annual changes in deadwood carbon: positive increment in the Mediterranean and Macaronesian regions, close to zero in the Atlantic region and negative in the Alpine region. We also found significant and positive relationships between the mean height and basal area on deadwood carbon stocks as well as a bell-shaped relationship between the mean diameter of living trees as a proxy of stand age on deadwood carbon stocks. The European Level I Monitoring Programme emerged as a useful tool to explore the dynamics of deadwood carbon. However, the temporal scheme and the lack of repeated measurements of dasometric inventories preclude forecasting future deadwood carbon stocks under alternative management regimes and climate conditions. In this regard, the deadwood data collected in future cycles, together with the deadwood data from the National Forest Inventory plots may allow the development of prediction models and therefore fulfill the international requirements on Member States for deadwood forecasts at national scale for the 2021 to 2030 period.