Forest carbon sink-timber compound management planning of Pangu Forest Farm in Great Xing’an Mountains of northeastern China

  Objective  To provide the optimal forest management paradigm for various forest types, the research of forest management in our country had mainly been performed on the scale of forest stand (or sample plot), however the importance of temporal and spatial configuration of alternative thinning treatments had been ignored for a long term. Therefore, a spatial explicitly forest management planning model was developed by integrating forest carbon increment objective into traditional timber harvest scheduling problem, which can provide some new theories and technologies for the multi-objective management of forest resources in China.

  Method  With the guidance of forest category management theory, a practical forest multi-objective spatial management planning model (FMS), including the forest timber production and carbon increments of aboveground tree-layer, was developed for the Pangu Forest Farm in Great Xing’an Mountains of northeastern China using the simulated annealing algorithm. To improve the practicality of the planning model, FMS subjected to the even-flow constraints of harvest volume, the inventory constraint of forest carbon stocks, and the spatial constraints of different thinning treatments. Based on FMS and the constraints of carbon trading and timber market in China, the optimal forest management plans for a 50-years planning horizon of Pangu Forest Farm was optimized. Then, the amount of timber harvest, the amount of carbon increments, and the temporal and spatial configuration of alternative thinning treatments for each period were quantificationally analyzed.

  Result  The joint net present value (NPV) of timber production and carbon increments during the 50-years planning horizon for Pangu Forest Farm was as large as 1.54 × 10⁸ CNY, in which the NPVs of timber production and carbon increments were 1.37 × 10⁸ and 0.17 × 10⁸ CNY, respectively when the carbon price was assumed as 120 CNY/t. The amount of harvest timber and carbon increments during the planning horizon were estimated as 1.78 × 10⁶ m³ and 1.68 × 10⁶ t, and the carbon stock of aboveground tree biomass was 5.99 × 10⁶ t, in which the carbon stock of aboveground tree biomass at the ending of planning horizon increased by 38.98% with respect to that at the beginning of planning horizon. Within the optimal management plan, the protected area, thinned area and no-thinned area accounted for 44.36%, 48.01% and 7.63%, respectively, in which the thinned area with high intensity accounted for 41.78% of the total forest area in this region. In addition, some significant differences were observed among the configuration of alternative management activities for each period, in which the amount of harvest volume and thinned area, as well as the number of thinned sub-compartments all accounted for approximately 90% of their gross for each period. The distributions of thinning treatments presented significantly spatial characteristics for the optimal management plans, however the pattern was all conformed with the constraints.

  Conclusion  The outputs of FMS have some significant advantages: (1) forest managers always can obtain some pediocratic economic benefits for each period due to the even-flow constraints of harvest volume; (2) the forest resources can be protected from over-harvesting due to the inventory constraints of carbon stocks, which are meaningful to promote the function of forest carbon sequestration; (3) the forest planning model can provide the optimal temporal and spatial configuration of forest management activities. Obviously, all these advantages are helpful for the multi-objective management of forest resources in our country. However, the values of some key constraint parameters still need further research to improve the practicality of the proposed planning model in future.