森林固碳释氧服务价值与异养呼吸损失量评估

固碳释氧是森林最重要的生态系统服务之一,将森林碳收支与固碳释氧服务价值评估相结合对于准确评估生态系统服务价值具有重要意义。应用森林碳收支模型(CBM-CFS3),分别基于净初级生产力(NPP)和净生态系统生产力(NEP)评估了2009—2030年湖北省兴山县森林生态系统总、净固碳释氧服务价值的时空动态,量化了异养呼吸造成的固碳释氧服务价值损失。模拟期间兴山县森林生态系统NPP逐渐增加(0.46—0.70 Tg/a),NEP由0.12 Tg/a先增加至0.21 Tg/a,然后逐渐下降至0.18 Tg/a;所对应的森林总、净固碳释氧服务价值范围分别为7.59—11.53亿元/a和2.21—3.70亿元/a。异养呼吸逐年增加,导致固碳释氧价值每年损失平均值为7.29亿元/a或4509元hm~(-2) a~(-1),约占总价值的68.6%。兴山县东南部异养呼吸造成的森林固碳释氧服务价值损失较高,而中部及西南部森林净固碳释氧价值较高。模拟期间兴山县森林为碳汇,稳定地提供固碳释氧服务。与NPP相比,使用NEP评估固碳释氧服务价值更为合理。忽视异养呼吸将严重高估森林生态系统固碳释氧服务价值;因而必须将物质循环过程与生态系统服务评估相结合,以降低评估结果的不确定性、提高生态系统服务的评估能力。

Evaluation of forest carbon fixation and oxygen release service value and heterotrophic respiration loss

Carbon fixation and oxygen release (CFOR) is one of the most important services provided by the forest ecosystem. It is crucial to combine the forest carbon budget with the CFOR service to conduct an accurate assessment of ecosystem service values. Using a forest carbon budget model (CBM-CFS3), this study evaluated both temporal and spatial dynamics of total and net CFOR service values based on estimation of net primary production (NPP) and net ecosystem production (NEP) of the forest ecosystem from 2009 to 2030 in Xingshan county, Hubei province, China. During the simulation period, the total NPP progressively increased from 0.46 Tg/a to 0.70 Tg/a, while the total NEP increased from 0.12 Tg/a to 0.21 Tg/a initially and then declined to 0.18 Tg/a. The total and net CFOR service values ranged from 759 to 1153 million RMB per year and from 221 to 370 million RMB per year, respectively. Heterotrophic respiration (HR) increased progressively with an average annual loss of CFOR value of 729 million RMB per year or 4509 RMB per hectare per year, which accounted for 68.6% of the total CFOR value. The HR loss was highest in the southeastern part of Xingshan, while the net value of CFOR was highest in the central and southwestern parts. The forest ecosystem in Xingshan acted as a carbon sink and provided the CFOR service steadily during the simulation period. Compared with NPP, NEP was more reliable for use in evaluating the value of the CFOR service. A severe overestimation of forest CFOR service value is likely to occur if the impact of HR is excluded. Therefore, to reduce the uncertainty in evaluation and enhance the capacity of ecosystem services assessment, it is necessary to combine the material cycle process with the ecosystem services assessment.