黄土丘陵区两种主要退耕还林树种生态系统碳储量和固碳潜力

Ecosystems carbon storage and carbon sequestration potential of two main tree species for the Grain for Green Project on China′s hilly Loess Plateau

黄土丘陵区是中华文明的起源地,而原有植被却遭受严重破坏。因此,自20世纪70年代末开始的三北防护林工程、退耕还林工程和天然林保护工程等大型生态恢复工程,在本区均有大面积分布。这些工程已经对生态恢复起到重要作用,并将对全球碳素循环起到积极作用。以黄土丘陵区的主要造林树种——油松(Pinus tabulaeformis Carr.)和刺槐(Robinia pseudoacacia L.)为研究对象,共设置样方28个,测定森林乔木、灌木、草本生物量及凋落物碳储量;钻取并分析土样516份,获得土壤有机碳储量。结合文献数据和农田碳储量数据,建立0—86年生油松林和0—56年生刺槐纯林生态系统碳储量-林龄序列;在此基础上分析造林对生态系统碳储量和固碳潜力的影响。结果表明,造林后的油松林和刺槐林生态系统的植被、凋落物及土壤碳储量逐渐增加;在没有人为干扰的情况下,19、27、36、86年生油松林生态系统碳储量分别为70.76、143.43、167.30、271.23—332.26Mg/hm2;8、17、39年生刺槐林生态系统碳储量分别为80.37、94.08、140.77 Mg/hm2。受间伐干扰、45、52年生油松林生态系统碳储量分别为136.42、168.56 Mg/hm2,相对于没有人为干扰的油松林,其植被碳储量明显下降,而土壤碳储量保持稳定甚至升高。受乱砍滥伐干扰的71年生油松林和56年生刺槐林的生态系统碳储量分别为118.87、76.99 Mg/hm2,相对于没有人为干扰的森林,其植被碳储量和土壤碳储量均呈明显下降趋势。种植油松林之后的86a时间内,其生态系统固碳潜力为211.61—272.64 Mg/hm2;而种植刺槐林、在39a时间内的生态系统固碳潜力为81.15 Mg/hm2。

The Loess Plateau covers 640000 square kilometers in Northwest China,and much of the Plateau′s terrain is hilly.Though the Plateau was a cradle of early civilization,its primary vegetation has been severely degraded in modern times.In response,beginning in the 1970s,several National Ecology Restoration Projects have focused on restoring the region′s ecological health.Among them are the Three-North Shelterbelt Project,the Grain for Green Project,and the Natural Forest Protection Project.These projects have played an important role in soil and water conservation,in some cases,reversing ecological destruction.In the future,these and other projects will play an important role in the carbon cycle.In this paper,we assessed the carbon storage and carbon sequestration potential of Chinese pine（Pinus tabulaeformis Carr.） and Black locust（Robinia pseudoacacia L.） planted forest on the hilly Loess Plateau.For our study,we established 28 plots and collected 516 soil samples to measure biomass carbon density of trees,shrubs,and herbaceous plants,as well as carbon storage in litter and soil.The plots contained 6 types of Chinese pine forests planted between the 1940s and 1990s,4 types of black locust forests planted between the 1950s and the 2000s,and 4 farmland plots,which served for comparison.The results showed that,following the afforestation,carbon storage increased gradually in vegetation,leaf litter,and soil for Chinese pine and black locust ecosystems,in the absence of human disturbance.The carbon storage was 70.76,143.43,167.30 and 271.23—332.26 Mg/hm^2 for the 19-,27-,36-and 86-year-old Chinese pine ecosystems,and 80.37,94.08 and 140.77 Mg/hm^2 for the 8-,17-and 39-year-old black locust ecosystems,respectively.Compared with the forest that in the absence of human disturbance,the 45-and 52-year-old Chinese pine ecosystems,which are recovering from thinning,had carbon storage of 136.42 and 168.56 Mg/hm^2,pose significant decline of vegetation carbon storage and the soil organic carbon storage keep stable or even increased,and the 71-year-old Chinese pine ecosystem and the 56-year-old black locust ecosystem,which had suffered significant timber poaching,had carbon storage of 118.87 and 76.99 Mg/hm^2,pose significant decline both of vegetation carbon and soil organic carbon.We take the carbon stock of cropland as the baseline,and take the forest plantation ecosystem,which in the absence of human disturbance,as the potential carbon storage.The carbon sequestration potential is 211.61—272.64 Mg/hm^2 for planting Chinese pine on farmland in 86 years,and 81.15 Mg/hm^2 for planting black locust in 39 years.Thus,planting Chinese pine and black locust,and weaken the human disturbance could both increase ecosystem carbon sequestration.With such an approach,the Loess Plateau will act as a significant carbon sink in the coming decades.