西藏草地多项供给及调节服务相互作用的时空演变规律

基于统计数据及MODIS产品,计算西藏草地2000与2010年载畜支持服务、肉类供给服务、水源涵养服务和碳吸收服务的功能量。构建Pearson相关系数、总生态系统服务(TES)、供给-调节服务互竞指数(TO),分析了4项生态系统服务相互作用关系随纬度、海拔及时间变化的规律。结果表明:西藏草地两项供给服务和两项调节服务之间分别为相互协同作用,且随时空变化不大。供给服务和调节服务之间的相互作用随海拔和纬度升高时,基本由相互竞争转变为相互协同,在高纬度时则无相互作用。4项服务在低纬度及低海拔呈相互竞争关系时,其生态系统服务总体水平也较低,中纬度及中高海拔呈协同关系时,其总体水平较高。从2000年到2010年,西藏草地4项生态系统服务皆发生较大变化。在变化中,12%的草地供给服务与调节服务发生相互竞争作用,33%的草地则为相互协同关系。发生相互竞争作用的草地主要集中在中低纬度的一江两河地区,而相互协同的区域主要为藏北羌塘高原中南部。

Spatiotemporal variation of interacting relationships among multiple provisioning and regulating services of Tibet grassland ecosystem

In 2000 and 2010, we quantified four ecosystem services in Tibet''s grassland ecosystem using recorded data and MODIS products. These four services were: grazing support, meat provisioning, water conservation and carbon sequestration. We established three indices: the Pearson correlation coefficient, total ecosystem services (TES) and a tradeoff index (TO). The interacting relationships among the four ecosystem services were analyzed using these three indices, taking into account the variation of interacting relationships, latitude, elevation and time. Positive Pearson correlation coefficients reflected the synergistic relationship between one pair of ecosystem services, with a negative correlation coefficient reflecting the tradeoff relationship. TES showed the total level of the supply of multiple ecosystem services. TO demonstrated the degree of the tradeoffs for one pair of ecosystem services. The results showed that two provisioning services-grazing support and meat provisioning-were synergistic, as were the two regulating services. Across the Tibetan plateau from 2000 to 2010, there was quite limited spatial or temporal variation in the synergetic relationships. However, the interacting relationships between the provisioning services and the two regulating services were variable. At lower latitude or elevation area of the Tibet, the provisioning services of grazing support and meat provisioning service were tradeoffs with both the regulating services of water conservation and carbon absorption service. However, as the latitude or elevation increased, the relationships between one provisioning service and one regulating service changed from tradeoffs to synergies. The synergetic relationships became weaker and even disappeared at the higher latitude area on the Tibetan Plateau. The TES coefficient also varied responding to the changing latitude and elevation. When latitude or elevation increased, the TES coefficient increased from a moderate level to a peak, then declined to near zero at high latitude or elevation. By comparing the changing curves in the Pearson correlation coefficient and TES, additional results showed that the total ecosystem service level was lower when the ecosystem services were tradeoffs and higher when they acted in synergy. From 2000 to 2010, there was little difference between the curves of Pearson correlation coefficient and TES responding to latitude or elevation variations. This suggested that the spatial variation mechanisms of interacting relationships among multiple ecosystem services did not differ much through time. However, from 2000 to 2010, all four grassland ecosystem services in Tibet changed. The variation in ecosystem services, including provisioning services, showed tradeoffs with regulating services in 12% of the grasslands and a synergetic effect in 33% grassland. The areas where provisioning services showed a tradeoff with regulating services during the changes occurring between 2000 and 2010 were located in the watershed of the Yarlung Zangbo, Nianchu and Lhasa rivers. The areas where provisioning services synergized with regulating services during the change between 2000 and 2010 were mainly located at the south edge of North Tibetan plateau. Our investigation of the spatiotemporal variation of interacting relationships among multiple provisioning and regulating services will contribute to the knowledge of best management practices in the Tibetan grassland ecosystem and concurrently promote grassland production and ecological security.