藏北草地退化与生态服务功能价值损失评估——以申扎县为例

藏北草地是我国重要的畜牧业生产基地和生态安全屏障。基于遥感和GIS技术,利用1990、2000、2010年3期不同时相的TM、ETM+和CEBERS遥感影像,对申扎县草地资源退化状况进行了遥感监测,并采用生态经济学评估模型对草地生态系统8个方面的服务功能价值损失进行了评估测算。结果表明:1990—2010年,申扎县草地退化面积增加了47.40×10~4hm~2,生态系统服务功能价值损失高达5.20×10~8元;其中1990—2000年,草地退化较严重,该时段也是生态系统服务功能价值损失较多的时期;2000—2010年,草地退化趋势变缓。藏北草地提供生物量价值仅约占生态系统服务功能总价值的7.0%,草地生态服务功能远大于其提供的生物量价值,因此必须从生态服务功能的的理念出发去经营草地,从而实现草地的可持续发展。

Dynamic monitoring of grassland degradation on the Northern Tibetan Plateau and loss assessment of its ecological service value, by using Shenza County as a case study

The grassland on the Northern Tibetan Plateau is an important livestock production base and ecological safety barrier in China. This paper uses the grassland ecosystem in Shenza County in a case study to establish an evaluation index system in order to monitor grassland degradation using remote sensing images (TM, ETM+, and CBERS in 1990, 2000, 2010) based on the landscape ecology, natural geography, and social economy of this region. The degradation of Shenza County grassland has been investigated over the past two decades through the interpretation of grass coverage information. The value loss of eight grassland ecosystem services was evaluated using models of ecological economics. The results show that the vegetation coverage of Shenza County changed significantly from 1990 to 2010. Grassland degradation has increasingly expanded, with moderate to severe degradation accounting for the largest proportion of the degradation. In 1990, the total area of degraded grassland was 62.07×10⁴ hm², with light degradation accounting for 18.71%, and moderate and severe degradation accounting for 10.97% and 7.45%, respectively. In 2000, the total area of grassland degradation covered 126.86×10⁴ hm², of which light degradation accounted for 34.46%, and moderate and severe degradation accounted for 33.02% and 12.20%, respectively. In 2010, the total area of grassland degradation was 109.47×10⁴ hm², with light degradation accounting for 40.02%, and moderate and severe degradation accounting for 22.19% and 8.08%, respectively.Grassland degradation was intensified in the period from 1990 to 2000, with the total degradation increasing by 64.79×10⁴ hm², of which light degradation accounted for 23.58×10⁴ hm², and moderately and severely degraded grassland accounted for 34.23×10⁴ hm² and 6.98×10⁴ hm², respectively, compared to the areas recorded in 1990. From 2000 to 2010, grassland degradation decreased by 17.39×10⁴ hm². Within this, lightly degraded grassland increased by 7.46×10⁴ hm², while moderately degraded and heavily degraded areas decreased by 18.01×10⁴ hm² and 6.84×10⁴ hm², respectively. The above analyses indicate that the grassland in Shenza County degraded between 1990 and 2000, and underwent gradual recovery from 2000 to 2010.The value of ecosystem services declined gradually during the period from 1990 to 2010, by 59.02×10⁸ Yuan in 1990, 52.14×10⁸ Yuan in 2000, and 53.82×10⁸ Yuan in 2010. The total value of the ecological services of the Shenza County grassland decreased by 5.20×10⁸ Yuan from 1990 to 2010, which included the values of the grass biomass services decreasing by 0.27×10⁸ Yuan, carbon storage and oxygen release decreasing by 0.36×10⁸ Yuan, nutrient cycle decreasing by 0.33×10⁸ Yuan, wind-breaking and sand fixation decreasing by 3.32×10⁸ Yuan, and biodiversity decreasing by 0.70×10⁸ Yuan. The value of water conservation, wind-breaking and sand fixation, and the biodiversity conservation account for the largest proportion, about 78% of the total value. The functional value of the ecosystem services decreased by 6.88×10⁸ Yuan from 1990 to 2000, and increased by 1.68×10⁸ Yuan from 2000 to 2010. Grassland degradation was significant, and the loss of ecosystem services peaked during the period from 1990 to 2000. The value of ecosystem services increased gradually from 2000 to 2010 because of the implementation of measures for environmental protection. However, the biomass value of the Northern Tibetan grassland accounts for only 7.00% of the ecosystem services the area provides. It is expected that grassland management carried out with attention paid to the functioning of ecosystem services will allow for sustainable development.