黄土高原生态系统过渡带土地覆盖的时空变化分析

在全球气候变化及其生态环境效应研究中,生态系统过渡带作为气候变化和人类活动的敏感区域,其土地覆盖的时空变化分析逐渐成为土地利用科学研究的热点问题。基于GIS的时空分析方法,在对Holdridge生命地带模型的判别标准进行改进的基础上,构建了生态系统过渡带的时空分析模型。在建立土地覆盖正向和逆向转换规则的基础上,构建了土地覆盖正向和逆向转换指数模型。并以黄土高原为案例区,在定量识别生态系统过渡带类型及其空间格局的基础上,定量评价了各种生态系统过渡带类型土地覆盖的转换情况。模拟分析结果表明,黄土高原地区共有14种生态系统过渡带类型,其总面积占整个黄土高原的25.21%。在1985-2005年期间,黄土高原生态系统过渡带内的耕地面积平均每10 a减少0.93%,而湿地和水体、林地、草地的面积则平均每10 a分别增加3.47%、0.24%、0.06%。整个过渡带区域土地覆盖的转换率从28.53%降低到21.91%,且其正向转换和逆向转换面积总体上均呈减少的趋势。另外,黄土高原生态系统过渡带区域和非过渡带区域的土地覆盖转换率对比分析显示,过渡带区域土地覆盖的转换率高于非过渡带区域。

Spatial-temporal Change of Land-Cover in Ecosystem Transitional Zones on the Loess Plateau of China

The ecosystem transitional zones (ETZs), expected to be among the most sensitive areas to climate changes and human activities, have higher landscape level species richness than in the adjacent ecosystems. The ecological position of land-cover in the transitional zones is prior to the adjacent ecosystems. Therefore, how to quantitatively identify and classify different ETZs and highly explicit their land-cover changes is important for improving the adaptation strategies to mitigate or even benefit from the projected impact of climate change on land use. In this paper, the Holdridge life zone (HLZ) model is improved to classify the ETZ type on the Loess Plateau of China. A positive and negative transformation index of land-cover (PNTIL) is developed to quantitatively evaluate the land-cover changes in every ETZ type. The results show that there are 14 ETZ types, accounting for 25.21% of the total land-cover area on the Loess Plateau. During the two decades from 1985 to 1995 and 1995 to 2005, cultivated land decreases 0.93% per decade, and wetland and water area, woodland and grassland increase 3.47%, 0.24% and 0.06% per decade, respectively, on an average. The total land-cover transformation rate of the whole ETZs decreases from 28.53% to 21.91%. The total, positive and negative transformed areas of land cover in ETZs have a decreasing trend during the two decades, in general. In both the transitional zones and adjacent biomes on the Loess Plateau, the area of cultivated land showed a decreasing trend, while the area of woodland showed an increasing trend during the two decades. Moreover, the transformation of land-cover types in the transitional zones is generally faster than the adjacent ecosystems. Our results provide a solid preliminary assessment of land-cover changes, indicating that the transitional zones are more affected by climate change and human activities on the Loess Plateau. The ecological diversity and patch connectivity of land-cover in all transitional zones generally showed an increasing trend during the period 1985 to 2005, with the same changing trend in all adjacent biomes. What’s more, the ecological diversity and patch connectivity of land-cover in all transition zones is higher than that of the adjacent biomes, which indicates that the transitional zones have higher ecological diversity and patch connectivity than the adjacent biomes.