林业活动对区域森林生物量碳源汇格局的影响——以南平市为例

林业活动在一定程度上影响着区域森林的时空分布格局和碳汇/源功能。明确并量化林业活动对区域森林碳汇功能的影响与空间分布,对于区域森林碳汇提升和实现区域"碳中和"具有重要意义。以国家级生态示范区福建省南平市为例,以多期森林资源规划调查数据为基础,采用IPCC材积源-生物量法,基于土地利用类型的时空变化和林业活动类型划分,分类分析了南平市森林碳源和碳汇的空间分布特征,并量化了不同林业活动（一直保持为森林、人工造林、自然恢复、毁林和森林退化）对森林碳汇和碳源的影响。研究结果表明,2013年南平市森林碳储量总量为80.84Tg C,2020年森林碳储量总量增加至89.87Tg C,年均变化量为1.29Tg C/a （或4.73Tg CO₂/a）。平均胸径、公顷蓄积等林分因子是当前主要影响森林碳储量的因素。在其他影响因素中,暗红壤分布区的森林生物质碳密度较高而在水稻土分布区则较低;此外,高海拔、中等立地质量土地上的森林碳密度较高。对于不同林业活动,2013-2020年南平市一直保持为森林（森林经营）、自然恢复增加的天然林和人工造林分别使森林生物质碳储量增加了0.34Tg C/a、0.85Tg C/a和1.05Tg C/a,同期因毁林和森林退化导致森林生物质碳储量分别减少0.75Tg C/a和0.42Tg C/a,森林生物质碳储量净增加1.09Tg C/a （或3.98Tg CO₂/a）,明显低于2013-2020森林碳储量净增量。对于土地利用变化较剧烈的区域,本文基于土地利用变化且区分林业活动路径的方法,能更准确地反映森林的碳汇和碳源及时空格局。2013-2020年间南平市一直保持为森林的生物质碳密度仅增长0.22Mg C hm^-2 a^-1,成熟林、过熟林面积占比增加使森林平均生长速率下降可能是主要原因。而同期通过自然恢复和人工造林使森林生物质碳密度分别增长4.00Mg C hm^-2 a^-1和4.10Mg C hm^-2 a^-1。优化龄组结构提升森林生长量、减少毁林和防止森林退化可以作为该区域未来森林增汇减排的有效举措。

Effects of forestry activities on regional forest biomass carbon source and carbon sink pattern: A case study in Nanping City

Forestry activities, to some degree, affect the spatio-temporal pattern of regional forest as a carbon sink or source. With the aim to improve regional forest carbon sink and achieve to "Carbon Neutral" strategically, it is of great significance to clarify and quantify the impacts forestry activities on forest carbon sink or source on spatial level. Taking Nanping City, Fujian Province, a national ecological demonstration, as an example, this paper analyzed the spatial distribution of carbon sources and carbon sinks caused by land use changes and five forest activities, which are remaining forest as forest, afforestation, natural recovery, deforestation and forest degradation, based on the local forest resources planning survey data during 2013-2020 and the IPCC volume-biomass method. The results showed that the total forest carbon storage in Nanping City was 80.84Tg C and 89.87Tg C in 2013 and 2020, respectively, with a mean annual change of 1.29Tg C/a (or 4.73Tg CO₂/a). Forest stand characters such as the mean Diameter at Breast Height (DBH) and the growing stock per hectare are the most important factors that mainly affect forest carbon storage. Among other influencing factors, the forest biomass carbon density is higher in the dark red soil distribution area but lower in the paddy soil distribution area, and it is higher in the high altitude, medium-quality sites. For the five forestry activities, the forest remaining as forest, natural restoration and afforestation increased the forest biomass carbon stocks (BCS) by 0.34Tg C/a, 0.85Tg C/a and 1.05Tg C/a respectively, while deforestation and forest degradation decreased BCS by 0.75Tg C/a and 0.42Tg C/a, respectively, which led to a net increase of forest BCS by 1.09Tg C/a (or 3.98Tg CO₂/a) in Nanping during 2013-2020. Significantly lower than the net increase in forest carbon storage in 2013-2020. For those regions with intense land use changes, our method based on land use change or forest activities could more accurately estimate regional forest carbon sink and carbon source and their spatial pattern. Forest remaining forest only increased the forest biomass carbon density (BCD) by 0.22Mg C hm^-2 a^-1 in Nanping during 2013-2020, which was likely due to average forest growth rate decreasing caused by the increase in the area proportion of mature and over-mature forests. However, the BCD was increased by 4.00Mg C hm^-2 a^-1 and 4.10Mg C hm^-2 a^-1 for the new natural forests and plantations during 2013-2020. Optimizing forest age group structure to improve forest growth, reducing area of deforestation and forest degradation could be the optional measures to increase regional forest carbon sink and reduce carbon emission from forest.