纸坊沟流域黄土丘陵区土地生产力变化与生态环境改善

该文以黄土丘陵区纸坊沟为研究区，系统分析了该流域土地利用变化及其对生态环境变化的影响，并深入探讨了土地生产力变化与生态环境改善间的关系及政策在其中的作用。结果表明，由于林草植被在控制水土流失方面的特殊作用，林灌草用地与农耕地间的相互转化，是导致流域生态环境发生变化的直接原因。在1958年，由于植被的彻底破坏，流域不仅土壤侵蚀剧烈，而且土地生产力也为历史最低水平，生态环境极度恶化。随着林草植被的恢复，尤其是随着退耕还林（草）工程的实施，流域生态环境得到明显改善。流域生态环境的变化与土地生产力的变化切相关。土地生产力的提高，可以有效地降低人均最小耕地面积，大大缓减了由于人口增长而引起的农耕地的扩张，间接促进农耕地向林草等生态用地的转移，有效地促进了生态环境的改善。政策可以通过新技术的推广等提高土地生产力进而促进生态环境的改善，但政策也可以通过直接的实物补贴等对土地利用结构产生影响，如退耕补贴。政策途径的选择与特定的社会经济条件有关。

Increase of land productivity and its implication for eco-environment improvement: a case study in Zhifanggou Catchment in loess hilly areas

Understanding the land use change and its impact on environment, and finding the underlying driving forces may be helpful to sustainable land use planning and ecological restoration. Using the GIS techniques, this paper analyzed land use changes and environmental status in Zhifanggou catchment in the period from 1938 to 2000 based on the data from aerial photos and field investigations. Meanwhile, the impact of policies on the land productivity and environment was also discussed. The results showed that the land use transformation between agricultural land and vegetation land determined the environment status of the watershed. In 1958, the watershed was not only seen the most severe soil erosion but also had the lowest land productivity due to completely destruction of vegetation and rapid expansion of farmland, thus resulting in the extremely devastated environment. After 1958, with the recovery of vegetation, especially with the implementation of the policy of "Conversion of Slope Farmland to Forest and Grass Plan" by the Central Government of China, the environment improved greatly and reached the highest level in 2000 during the research period. The analysis of land productivity changes showed that the increase in land productivity contributed most to this process. It greatly reduced the minimum farmland area required per capita and mitigated the pressure on expansion of farmland due to population increase, and facilitated the conversion of farmland to forest, shrub and pasture, indirectly improving the environment in this watershed. The policies can improve the land productivity by adopting and extending new techniques and methods thus improving the environment, yet direct subsidies such as food and money can also have the same effect. What policies should be made depends on the social and economic development as well as specific conditions.