退耕还林对宁南黄土丘陵区景观格局的影响——以中庄村典型小流域为例

"退耕还林"工程是关系到西部乃至中国生态恢复的重要工程。以黄土丘陵区"退耕还林"工程实施最早的典型小流域——中庄村小流域为研究区,应用景观生态学的原理与方法,选择斑块多样性、景观异质性和土地利用相对合理性等指数,对其退耕还林前(1993-2000年)后(2000-2005年)的变化情况进行分析,目的在于揭示"退耕还林"政策的实施对景观格局向良性演化的巨大推动作用。结果显示,退耕前(1993-2000年)研究区景观格局演变幅度很小,相应的,斑块多样性、景观异质性和土地利用相对合理性指数等景观指数的变化均较小。退耕后(2000-2005年),研究区发生了剧烈的景观格局演化,主要的景观变化过程是耕地转化为林地。此阶段研究区25°以上坡耕地基本退耕完毕,15-25°坡度范围是退耕还林的主要区域,其次为8-15°。相应的,2000-2005年小流域景观斑块总数减小,平均斑块面积增加,景观形状趋于复杂,斑块边界复杂性有所增加,景观斑块呈现团聚化的趋势。其中,耕地斑块总面积显著减小,斑块数下降,平均斑块面积略有增大;林地斑块总面积显著增加,斑块数保持稳定,景观优势度显著增加。土地利用相对合理性指数因此从1993年和2000年的0.668、0.664,显著上升至2005年的0.712。采用3期土地利用现状图对"退耕还林"实施前后两个阶段的景观格局演变过程进行分析,结果表明"退耕还林"是研究区景观格局良性演化的主要驱动力。

Impact of grain for green project on landscape pattern in hilly loess region in Southern Ningxia: landscape evolution process assessment of Zhong-zhuang-cun small watershed in 1993-2005

Grain for Green Project is one of the most critical programs due to its potential benefits in improving the ecological environment in China. In this paper, a case study on the impact of Grain for Green Project on landscape pattern was carried out in the Zhong-zhuang-cun watershed in hilly loess region in Southern Ningxia by using methods and theories of landscape ecology. The landscape metrics i.e. landscape structure, landscape heterogeneity and land use suitability were compared between 1993-2000 and 2000-2005, two stages before and during implementation of Grain for Green Project. The results indicated that the metrics of landscape structure, landscape heterogeneity and land use suitability as well as landscape pattern changed slightly in 1993-2000. But the landscape evolved tremendously in 2000-2005. The major transformations of landscape are cropland and unused land to forestland. The croplands over 25° were almost converted to forestland. The patch number of study area decreased, mean patch size increased and shape and edge metrics of landscape got complicated. Consequently, land use suitability increased significantly to 0.712 in 2005 from 0.668 in 1993 and 0.664 in 2000. The findings imply significantly that the Grain for Green Project is the main positive driving force of landscape evolution by two stages before and during GGP via employing three periods of land use maps.