城市扩张对农田景观中非农生境的影响——以辽宁省沈阳市沈北新区为例

Effect of urban expansion on non-agricultural habitats in farmland landscape: A case study of Shenbei New District, Shenyang City, Liaoning Province

农田景观因其巨大面积和更高的生产力,在全球生物多样性维持,甚至濒危物种的维持中扮演着重要角色。而农田景观中非农生境被蚕食的现象较为突出,尤其城市周边农田景观中更为普遍。本文以沈阳市沈北新区为例,采用景观紊乱度法将其划分为城市、城市边缘区和乡村3个区域,利用GIS技术分析3个区域农田景观中非农生境类型、数量与面积比例,探讨城市扩张对农田景观中非农生境影响程度。结果表明,随着与城市中心距离的增加,由城市、城市边缘区至乡村,非农生境类型呈现逐渐增加趋势,靠近城市中心的非农生境仅有林地,而在乡村区域有草地、林地、水域和农村道路4种类型。非农生境斑块数量比例呈现总体增加趋势,城市平均比例为8.63%、城市边缘区平均比例为17.08%、乡村平均比例为22.48%。非农生境面积比例呈现先增后减的倒"U"字型变化,城市边缘区的非农生境面积比例最高,值为1.93%。非农生境斑块密度呈现先增加、再减少和后增加的变化趋势,城市边缘区的非农生境斑块密度最小。最大斑块指数和聚集度指数呈现先减少后再增加的趋势,城市边缘区的非农生境最大斑块指数和聚集度指数最小。景观形状指数和多样性指数呈现先增加后减少的趋势,城市边缘区景观形状指数和多样性指数最大。总体而言,距离城市中心最近的城市区域受城市化强烈影响后,保留在城市景观之中的农田景观重新建立一种相对稳定的景观格局,残留其间的非农生境类型单一、斑块数量低,斑块较大、形状规则;正在受到城市建设切割的城市边缘区农田景观中非农生境面积比例、景观形状指数和多样性指数表现为虚高,但其斑块密度、最大斑块指数和聚集度指数均较小;距离城市中心最远的乡村区域非农生境受城市化影响较弱,类型趋于多样、斑块数量比例高、景观异质性较高。

Farmland landscape area accounts for 38% of the Earth’s land surface. Farmland landscape is very important for the protection of biological diversity and endangered species. Modern agriculture is characterized by industrialization and high yield, simplifying biodiversity and weakened function of biodiversity protection of farmlands. Non-agricultural habitats in farmlands are natural and semi-natural habitats including grasslands, forests, hedges, country roads, ditches. There are plenty rare species in non-agricultural habitats that are very important for the conservation of biodiversity, landscape structure and agricultural yield. However, severe changes in non-agricultural habitats （including grassland, forests and pools） have led to such lands converting into arable lands. This is the predominant phenomenon in suburban farmlands in China. Thus this paper analyzed the influence of urbanization on non-agricultural habitats by transecting farmland landscapes in Shenbei New District in Shenyang City, Liaoning Province. Firstly, the Shenbei New District was divided into city area, urban fringe area and rural area based on landscape disorder grade. Secondly, ten sampling bands were set up outward from the center of city. Four sampling bands were in city area, four in urban fringe area and two in rural area. Thirdly, the type, patch number and area proportion of non-agricultural habitats across sampling bands were analyzed in GIS. The results showed that non-agricultural habitats gradually increased with increasing distance from city area to urban fringe area and rural area. There was only forest in nearby city farmlands. There were grasslands, forests, pools and patches in rural farmlands. The proportion of patch number of non-agricultural habitats also gradually increased from city area to rural area. The average proportions of patch number were 8.63% in city area, 17.08% in urban fringe area and 22.48% in rural area. However, the proportion of patch area of non-agricultural habitats followed a inversed U-shape pattern of change from city area and urban fringe area to rural area. The maximum proportion of patch area in urban fringe area was 1.93%. The patch density of non-agricultural habitats gradually increased initially, then decreased and finally increased, with the minimum patch density in urban fringe area. Also the largest patch index and aggregation index gradually decreased initially and then increased, with the minimum largest patch index and aggregation index in urban fringe area. Landscape shape index and diversity index gradually increased initially and then decreased, with the maximum landscape shape index and diversity index in urban fringe area. In general, non-agricultural habitats in city area had single type, low proportion of patch number, larger patch and the regular shape drastically affected by urbanization. It was falsely apparent that the proportion of patch area, landscape shape index and diversity index in urban fringe area were highest due to disturbance of farmlands by urban construction. However, it was lower in patch density, largest patch index and aggregation index. Non-agricultural habitats in rural area had diverse types, high proportion of patch number and high landscape heterogeneity. The result of this research was a significant reference for increasing biodiversity and heterogeneity of non-agricultural habitats for improved health of farmland ecosystems.