Thinned northern German Scots pine forests have a low carbon storage and uptake potential in comparison to naturally developing beech forests

Abstract

In Europe, production forests with conifers widely replace native broadleaf trees. In the Pleistocene lowlands of northern Germany, > 1.7 million hectares of pine forests (Pinus spp., mostly P. sylvestris) have replaced natural broadleaf forests. We compared aboveground biomass carbon (C) pools and net primary productivity (ANPP) of broadleaf forests with natural development (ND; mostly Fagus sylvatica or Quercus petraea forests; 146 years old on average) to nearby young pine forests (YP; 65 years old on average) and old pine forests (OP; > 90 years) in northern Germany. Study aims where (i) to estimate the aboveground biomass C loss resulting from forest transformation, (ii) to compare the ANPP of broadleaf and pine forests, and (iii) to identify the main factors causing differences in biomass C storage and ANPP between forest types. YP forests stored only half of the biomass C of the ND forests (means: 72 vs. 147 MgCha−1); OP stands exceeded YP stands only by ~20% (87 vs. 72 MgCha−1). The main factor driving the biomass C pool differences was tree species identity, while stand age was not influential. Mean ANPP was 1.1 MgCha−1year−1 higher in ND forests than in YP stands due to higher litter production, while wood production was similar. We conclude that large-scale forest conversion to Scots pine forests has decreased the aboveground biomass carbon storage by half and the C sequestration potential with aboveground productivity by ~25%; this effect must be assessed together with changes in soil organic carbon stocks.