用RS和GIS技术评价福建省长汀县土壤保持功能对生态系统变化的响应

人类活动直接影响生态系统的变化,而生态系统变化又改变着其土壤保持功能。通过对生态系统及其土壤保持量变化的对比分析可以发现两者间响应机制,分析水土保持工作的得失,并进而为下一步治理提供指导。基于e Cognition平台利用landsat影像解释出长汀县2000、2010和2016年的生态系统类型,并利用RULSE模型定量评估土壤保持功能,探讨土壤保持量相对于生态系统变化的响应规律。结果表明:2000—2016年间,长汀县生态系统变化主要表现为两大特征:其一是低覆盖类型向高覆盖类型转变,表现为稀疏林大量地转为常绿阔叶林和常绿针叶林,研究期内稀疏林减少14729.38hm~2(减幅56.75%),而常绿阔叶林和常绿针叶林分别增加6791.50hm~2(增幅23.21%)、10228.07hm~2(增幅5.80%);其二是受经济利益驱动,大量耕地和常绿针叶林转为城镇和茶果园,研究期内城镇、茶果园分别增加4469.14hm~2(增幅85.43%)、1949.32hm~2(增幅69.38%)。研究期内全县土壤保持量显著提高,单位面积土壤保持量从2000年217.32t hm~(-2)a~(-1)提高2016年246.02t hm~(-2)a~(-1)。各生态系统中,常绿阔叶灌丛和常绿阔叶林土壤功能最强,单位面积土壤保持量大于277t hm~(-2)a~(-1),而城镇土壤保护功能最弱,单位面积土壤保持量低于65t hm~(-2)a~(-1);研究期内大部分生态系统的土壤保持能力有不同程度提高,只有城镇和茶果园下降,单位面积土壤保持量分别减小21.03t hm~(-2)a~(-1)和16.74t hm~(-2)a~(-1),这说明城镇和茶果园迅速扩张可能引发新的水土流失。从空间上看,土壤保持量提高的区域占全县96.5%,其中东北部森林区和中南部增幅最显著,说明了十几年的水土流失综合治理工作极具成效;另一方面土壤保持量下降的区域散布于人类活动较频繁的各个山间盆谷,其中汀州、大同最为集中,迅速的城镇化与茶果园开发是造成保土功能下降的主要原因。

Responses of soil conservation function to ecosystem changes: an assessment based on RS and GIS in Changting County, Fujian Province

Soil conservation is one of the most important eco-services. Human activities which contain soil erosion control affect ecosystem changes, and ecosystem changes are also closely related to soil conservation. By comparative study of the changes of ecosystem and soil conservation, we can find out the interaction mechanism between them, understand the gain and loss of soil and water conservation work in the past, and provide guidance for further treatments. In the paper, the Landsat images are used to explain the ecosystem types of Changting County in 2000, 2010 and 2016, the whole study is based on the eCognition platform. Then a quantitative evaluation of soil conservation is conducted through the RULSE (Revised Universal Soil Loss Equation) model, in which, the quantity of soil conservation is the difference between the potential of soil erosion and the reality of soil erosion. Further, a statistical analysis is performed to explore deep reasons of soil conservation function changes from the perspective of ecosystem changes. Results show that there are mainly two characteristics of ecosystem changes during 2000 and 2016 in the county. One is the change from low cover types to high cover types, characterized by large quantity of sparse forest turning into evergreen broad-leaved forest and evergreen coniferous forest. During the years, the area of sparse forest decreased by 14729.38 hm² (-56.75%), and evergreen broad-leaved forest and evergreen coniferous forest increased by 6791.50 hm² (23.21%) and 10228.07 hm² (5.80%), respectively. The other is that a large number of cultivated lands, grasslands and evergreen coniferous forest, driven by economic interests, were turned into towns and tea orchards. During the study period, towns and tea orchard increased by 4469.14 hm² (85.43%) and 1949.32 hm² (69.38%), respectively, paddy field and dryland decreased by 707.85 hm² (-2.65%) and 344.31 hm² (-13.66%) respectively. Soil conservation quantity in the county increased significantly during the study period, and soil conservation quantity per unit area is 217.32 t hm^-2 a^-1 in 2000 and 246.02 t hm^-2 a^-1 in 2016, respectively. Among all the eco-systems, the evergreen broad-leaf shrub and evergreen broad-leaved forest soil possess the greatest soil conservation quantity, which are more than 277 t hm^-2 a^-1 per unit area, but the quantity per unit area of soil conservation of urban is the smallest, below 65 t hm^-2 a^-1. Soil conservation per unit area of most of the ecological system has improved in different levels, while that of towns and tea orchards has slightly degraded, with soil conservation quantity per unit area decreasing by respectively 21.03t hm^-2 a^-1 and 16.74t hm^-2 a^-1. It shows that a great expansion of towns and tea orchards may cause new soil and water loss. In terms of space, the areas with soil conservation improvement account for 96.5% of the county, the northeast forest area and the south-central region show the most significant improvement, suggesting that the comprehensive control of soil and water loss is highly effective; On the other hand, the area of degraded soil conservation scatters in those basins where human activity is frequent, among which Tingzhou and Datong is most prominent, suggesting that rapid urbanization and development of tea orchards is the main cause of soil conservation function decline.