黄土高原植被覆盖变化对生态系统服务影响及其阈值

黄土高原是退耕还林工程的核心区域,是中国生态恢复成效最显著的区域。明确黄土高原植被恢复对生态系统服务的影响,识别植被影响的阈值效应,是学术研究和管理实践共同的需求。然而,目前相关研究仍存在研究空缺,特别是在区域尺度对生态系统服务随植被变化阈值进行识别的研究较少。本文选择植被覆盖度（FVC）为指标表征2000—2015年黄土高原植被恢复情况,以土壤保持服务、产水服务和碳固定服务为指标表征研究区生态系统服务情况,对二者的时空变化及交互作用进行分析,评估植被覆盖变化对生态系统服务的影响,并对影响的阈值进行定量识别。结果显示：① 2000—2015年黄土高原植被显著恢复;生态系统服务变化差异明显,碳固定服务明显增强,土壤保持服务得到一定改善,产水服务较为稳定。② 植被覆盖变化与生态系统服务变化的相关程度存在差异,植被覆盖与碳固定服务的关联性最强,其次为土壤保持服务。③ 植被覆盖增加能够促进区域生态系统服务总体提升,但促进作用存在阈值效应。植被覆盖影响的阈值在林地区、林地—草地区、草地区和草地—沙漠区分别为44%、32%、34%和34%,超过上述阈值,植被覆盖增加的促进作用趋于减弱。

The effects of vegetation coverage changes on ecosystem service and their threshold in the Loess Plateau

The Loess Plateau is the core region of the "Green to Grain" Program, which makes it become the most successful example of ecological restoration in China. It is the common demand of both academic research and management practice to analyze the effects of vegetation restoration on ecosystem service and identify the threshold effects of vegetation restoration. However, there still is a research gap in related studies, especially for the thresholds of vegetation in the ecosystem service change at regional scale. In this study, we chose the fractional vegetation cover (FVC) as an index to indicate the vegetation coverage change in the Loess Plateau in 2000-2015, and took soil conservation service, water yield service and carbon sequestration service as indexes to exhibit the ecosystem service changes. The spatiotemporal changes of vegetation coverage and ecosystem services and their interaction were quantitatively analyzed. On such a basis, we further assessed the effects of vegetation coverage change on ecosystem services and quantitatively identified their thresholds. The results indicated that: (1) The vegetation coverage significantly improved in 2000-2015. Meanwhile, the differences of ecosystem service changes were prominent, with the carbon sequestration service getting significant enhancement, soil conservation service getting certain improvements and the water yield service maintaining steady. (2) There are differences among the correlations between vegetation restoration and changes of ecosystem service. The correlation of vegetation coverage-carbon sequestration service was the strongest, followed by that of vegetation coverage-soil conservation service. (3) The vegetation restoration could promote the improvement of the overall level of regional ecosystem service. Furthermore, we revealed the threshold effect in the promotion. The threshold occurrence resulted in the decrease of promotion efficiency of vegetation restoration, with vegetation coverage reaching 44%, 32%, 34% and 34% in forest zone, forest-grass zone, grass zone and grass-desert zone, respectively.