Carbon stocks, partitioning, and wood composition in short-rotation forestry system under reduced planting spacing

Key message The use of reduced planting spacings is an important strategy to increase the carbon storage in the above-belowground biomass and should be recommended for future exploitation of forest energy plantations when the purpose intended is the production of biomass for energy. Context Recent concerns about global warming have resulted in more concerted studies on quantifying carbon storage in forest systems. Forest energy plantations play an essential role in the carbon storage. Aims We proposed to evaluate the carbon storage and partitioning in short-rotation forest plantations and to characterize the elemental composition and energetic properties of the forest speciesEucalyptus grandisW. Hill ex Maiden,Mimosa scabrellaBenth, andAteleia glaziovianaBaill, grown under four planting spacings in Southern Brazil. Methods A field study was conducted in order to evaluate forest carbon stock and wood composition using samples collected by direct method. The four spacings evaluated were 2.0 x 1.0, 2.0 x 1.5, 3.0 x 1.0, and 3.0 x 1.5 m. Results TheEucalyptus grandisstored 327.1 Mg C ha(-1)at 2.0 x 1.5-m spacing. When compared with the 3.0 x 1.5-m spacing, we observed a reduction of 29% in carbon stored. All forest species showed higher carbon storage in the following partitioning pattern: trunk>roots>branches>leaves>litter. Forest species energetic properties and elemental composition were not affected by planting spacing. On the other hand, variations according the tree portions were observed. For the carbon stocks in the soil, we observed an average accumulated carbon stock for the forest species studied of 77.4 Mg C ha(-1)(0-40 cm). Conclusion Forest managers can accelerate growth and increase the forest carbon storage and biomass yield by using reduced planting spacing that are smaller than the current pattern used by the majority of the forest producers, which is 3.0 x 1.5 m. ForEucalyptus grandisandMimosa scabrella, the planting spacings recommended to produce biomass and improve carbon stocks were 2.0 x 1.5 and 2.0 x 1.0 m, respectively.