采伐限额对大兴安岭盘古林场森林碳汇强度的长期影响

Long-Term Effects of Harvest Quota on Forest Carbon Sink Intensity of Pangu Forest Farm in Great Xing’an Mountain,Northeast China

【目的】探明采伐限额对林场尺度森林碳汇强度及其持续时间的影响规律和机制,量化不同采伐限额对林场尺度森林多目标经营决策的影响,为全面提升森林质量和碳汇功能提供理论基础。【方法】以大兴安岭塔河林业局盘古林场为例,模拟退火为优化算法,考虑活立木、枯死木、枯落物、木材产品、采伐/加工以及替代效应的碳库,建立以木材生产、生物质能源和碳汇综合收益最大化为目标的经营规划模型,并量化不同采伐限额(情景1:每分期0 m^(3);情景2:每分期19000 m^(3);情景3:每分期38000 m^(3);情景4:每分期56000 m^(3))对100年规划期(10个分期,每分期10年)内经济收益、木材产量、生物质能源产量、碳汇量以及经营措施的综合影响。【结果】当仅考虑碳汇收益时,规划期内盘古林场的总经济收益为15416.19×10^(4)yuan;随着采伐限额的增加,规划期内总经济收益呈明显增加趋势,情景2,3和4分别较情景1增加19.74%、39.14%和58.81%;各分期净碳汇量随着规划分期的增加呈明显降低趋势,而各分期林地碳储量呈明显增加趋势;整个规划期内平均碳汇量0.16~0.24 t·hm^(-2)a^(-1),规划期末林地碳储量高达77.47~77.90 t·hm^(-2),较规划期初增加约48.07%;规划期内中径材蓄积比例呈增加趋势(从5.80%到36.18%),而小径材比例呈明显下降趋势(从45.74%到16.09%),但短小材比例则相对稳定(平均43.98%);各情景中生物质能源产量与木材产量密切相关,其比值分别为0.2437、0.2497和0.2477,整体以收获树干(45.70%)和树根(36.03%)中的生物质能源为主;情景2~4中,平均每分期采伐面积分别为890、1742和2385 hm2,整体以轻度择伐为主(从75.08%到67.65%),但中度(从17.98%到22.25%)和重度(从6.95%到10.10%)择伐面积比例呈明显增加趋势。【结论】长远来看,适当增加大兴安岭地区的森林采伐限额不仅能够增加森林的碳汇强度,还能够显著延长碳汇的持续时间。

【Objective】This study aims to explore the rule and mechanism of the influence of logging quotas on the intensity and duration of forest carbon sequestration at the forest farm scale,which would help to quantify the impact of different logging quotas on multi-objective forest management decisions at forest farm scale,so as to provides a theoretical basis for improving forest quality and carbon sink function.【Method】A management planning model that aims to maximize the comprehensive benefits of timber production,biomass energy production and carbon sequestration was developed using simulated annealing algorithm for Pangu Forest Farm of Tahe Forestry Bureau in Greater Xing’an Mountains,in which the carbon pools of living biomass,dead wood,annually litter,wood products,logging/processing and the substitution effects of wood production and bioenergy were considered simultaneously.Then,the effects of four different logging quotas(scenario 1:0 m^(3) per period;scenario 2:19000 m^(3) per period;scenario 3:38000 m^(3) per period;scenario 4:56000 m^(3) per period)on economic benefits,wood production,biomass energy production,carbon sequestration and management activities were quantified for a horizon of 100 years(1010-year periods).【Result】The total economic benefits of Pangu Forest Farm during the planning horizon was 15416.19×10^(4)yuan,when only the benefits of carbon sequestration were considered.With the increases of the logging quota,the total economic benefits during the planning horizon showed significant increase trends,which were approximately 19.74%、39.14%and 58.81%when compared with Scenario 1.The net carbon sequestration of each period decreased significantly with the increases of planning periods,while significant increasing trends were observed for the carbon stocks of each period.The average carbon sequestration during the entire planning horizon were about 0.16-0.24 t·hm^(−2)a^(−1),and the carbon stocks at the ending of planning horizon on forestland were as large as 77.47-77.90 t·hm^(−2),namely approximately 48.07%increases were observed when compared that with the beginning of planning horizon.During the planning horizon,the proportion of medium-size timber increased significantly with the planning period(from 5.80%to 36.18%),while significant decreased trends on the proportion of small-size timber could be observed(from 45.74%to 16.09%),but the proportion of short-and small-size timber was always relatively stable(43.98%on average).The production of biomass energy was highly related with wood production for each scenario,and the ratios between bioenergy and wood production were 0.2437,0.2497 and 0.2477,respectively,where the harvesting mainly focused on the trunk-(45.70%)and roots-(36.03%)components.The assigned average harvest area for scenarios 2−4 were 890,1742 and 2385 hm2 per period,respectively.The harvested areas mainly focused on the mild-selective cutting(from 75.08%to 67.65%),but the proportion of moderate-(from 17.98%to 22.25%)and severe-(from 6.95%to 10.10%)selective cutting both increased significantly with the increases of planning periods.【Conclusion】From the long perspective of viewpoint,improving the logging quota appropriately within the region of Greater Xing’an Mountains can not only increase the intensity of forest carbon sequestration,but also significantly extend the duration of carbon sequestration.