西南丘陵山区农村道路构建及其景观效应
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摘要
近年来,农村道路作为农村基础设施建设重点之一,在农村土地综合整治、新农村建设、城乡统筹发展平台上,得到了迅猛扩展。目前,对大地貌单元内高等级道路系统关注较多,如高速公路、铁路、国(省)道或县道等路网联贯对沿线物流和信息交换的集聚与辐射,所具有“通道-阻隔”效应对大地貌单元地表覆被和景观利用的异质性和多样性的驱动及其对生态系统的影响。低等级的农村道路则集中于道路网布局与评价、道路工程设计与造价的控制、工程施工与质量监管、养护管理、以及路面排水、边坡水土流失与道路侵蚀防治等方面的研究。然而,在西南丘陵山区广泛分布的农村道路,不仅受到人为经济活动的影响,而且深受自然环境条件的制约,农村道路建设及其运营过程为社会发展提供保障,促进经济发展的同时,也带来了自然景观和生态系统的分割、干扰、破坏、退化等景观生态问题。为此,本文通过实地调研西南丘陵山区农村道路现状,选取了四川省雅安市芦山县飞仙关镇凤凰、三友2个行政村(样区Ⅰ),贵州省桐梓县九坝镇白盐井、水河、槐子3个行政村(样区Ⅱ),重庆市合川区大石镇高川、柿子、竹山、懑井4个行政村(样区Ⅲ),重庆市秀山土家族苗族自治县梅江镇新联、关田2个行政村(样区Ⅳ)和重庆市忠县拔山镇拔山、石联、苏家3个行政村(样区V)等五个样区,分析了不同地形地貌、水文地质、气候、土壤、植被等地理环境和农业人口、耕地数量、人均耕地、基础设施、农业生产条件、耕作制度和经济发展水平等社会经济综合要素融合下的农村道路类型与功能,明确了西南丘陵山区经济发展的现状及其未来发展态势对农村道路的需求,结合当地农业机械使用状况及常用建材特色,研究了农村道路路面(基)控制等结构层次工程设计技术,构建西南丘陵山区农村道路体系,分析了农村道路体系的网络特征和景观效应,从而为西南丘陵山区农村道路体系布局与设计提供理论和技术支撑。
(1)农村道路布局
农村道路按功能和路面宽度可分为田间道和生产路两级。田间道应沿田块的短边布设,在旱作地区,田间道也可布设在作业区的中间,沿田块的长边布设,使耕作机械两边均可进入工作小区以减少空行。在梯田区布置田间道应按照具体地形,采取通梁联峁,沿沟走边的方法布设。田间道多设置在沟边、沟底或山峁的脊梁上。山低坡缓,田间道呈斜线形；山高坡陡,田间道可呈“S”形、“之”字形或螺旋形迂回上山；生产路宜纵横交错布置,因地制宜地与田间道形成网状,设在田块的长边,并分旱地区和水田区采取不同的方式布置。旱地横向生产路为40～200m,布置一条生产路。在石坎较多的地区可与石坎结合设置,以节约用地。纵向生产路多布置在丘陵山地的脊部,根据田面长度,一般200～500m布置一条。如果生产路与沟渠组合设置不利于排水或不利于通行时,应分开布置。水田生产路可设置在农沟外侧与田块直接连接。横向生产路可间隔100～300m布置一条,纵向生长路可间隔200～500m布置一条；与紫色岩溶区相比,石灰岩溶区的地质条件更具有复杂性,应绕避溶蚀洼地、溶洞发育区和大断层破碎带。农村道路应尽可能地结合地形地貌条件及生产方式进行布置,体现因地制宜原则。田间道可与支、斗渠沟结合布置,生产路可与农渠沟结合布置。因此,西南丘陵山区农村道路布局不仅要充分考虑农村居民点分布、农田水利设施和耕作田块设置等,还应顺应自然环境条件、融于农业自然人文景观。
(2)农村道路工程设计
紫色岩区路面设计高出原地面约20～30cm,路面垫层采用20cm厚手摆片石,路面基层为10～15cm泥结碎石稳定层,路面面层采用15～20cm厚C25～C30水泥混凝土进行铺设。该区域土基强度较高,可采用原土路基夯实,压实度在90%以上。路基的宽度为4.5～5.0m,边坡采用1：1.5。同时考虑到本区域降雨期较长,集雨面积较大,可在路基来水一侧布设边沟,沟底宽0.25～0.30m、净深0.3～0.4m,沟壁采用M10～M15水泥砂浆砌毛条石或浆砌块石,沟底铺设8～10cm厚C15～C20水泥混凝土。为了保证路基的稳定,设计在田间道的另一侧利用条石修建条石路肩、预制混凝土或土质路肩；石灰岩溶地区常常遭受两侧山坡水土的冲蚀,三水转化快,因此,路基和路面设计比紫色土区厚,高出原地面约30～40cm。路面垫层采用20cm厚手摆片石,路面基层为15cm泥结碎石稳定层,路面面层采用18～20cm厚C30水泥混凝土进行铺设。路面宽度净宽为3.5～4.5m,横坡为0.3%～0.5%；田间道的平曲线半径(转弯半径)应不小于15m,特殊困难地段不得小于10m,平曲线长度不得少于15m。当平曲线半径等于或小于150m时,应在曲线上设置超高,在曲线内侧加宽,并在平曲线两端各设置一段不少于10m的超高缓和段,超高横坡度最大值不超过8%,积雪冰冻地区不超过6%。田间道最大纵坡宜取6%～8%,特殊情况下,丘陵地区不宜大于11%,山区不宜大于13%；在海拔2000m以上或严寒冰冻地区不宜大于8%。无论是紫色岩区还是石灰岩溶区,当田间道路面宽度小于4.0m时,均应在适当距离内设置错车道。错车道应设在有利地点,并使驾驶员能看到相邻两错车道间驶来的车辆。设置错车道路段的路面宽度不应小于6.5m,间隔宜为300～600m,有效长度宜为15～25m；紫色岩区生产路宜采用片石、块石垫层,路基宽宜为0.6～2.7m,路面宽度设计为0.6～2.5m。无积水和流水冲刷的地区可采用夯实素土路基,生产路路基宜高于路面0.1～0.2m。石灰岩溶区宜采用浆砌石质路基,高出田面高程0.2～0.5m。生产路路面均可采用砼现浇、预制砼板、青石板等材料,砼路面厚度宜为5～20cm,预制砼板、石板宜为6～15cm,其他材料宜为8～20cm。田间道、生产路跨越沟渠或溪沟处可布置农桥,农桥分为田间道桥和人行便桥。结构设计安全等级不低于三级。农桥的结构形式可采用梁式和拱式。建筑材料可用砖、石、混凝土及钢筋混凝土等。道路穿越渠道时,宜在渠、路下或地下设置涵洞。涵洞的顶端距路基要有一定的距离为20～30cm。涵洞水流的方向,应与洞顶填方沟渠或道路正交,与原水道的方向一致。涵洞的形式可采用圆形、箱形、盖板式和拱式等,选用混凝土或钢筋混凝土管。因此,西南丘陵山区农村道路工程设计,除充分考虑道路所经路段的地质地貌、水文、土地利用类型和土壤特性外,还应就地取材,降低建造成本。
(3)农村道路体系网络特征
五个样区自然条件与社会经济等差异加剧了区域各级道路体系构建重点的差异,但整体上道路体系均更加趋于健全和完善,网络特征存在一定差异但有所缩小。从廊道指数来看,五个样区农村道路建设后较建设前的总长度、密度均有不同程度增加。建设前,各行政村道路总长度变化范围为6.73km～76.36 km,相差11.4倍,建设后其为7.88km～82.15km,变化范围缩小至10.4倍；建设前,道路网络密度为38.18 m/hm2～149.6 m/hm2,相差近4倍,建设后其为65.87 m/hm2～159.6 m/hm2,相差仅2.4倍。此外,五个样区农村道路建设前后道路类型组合的结构变化也较为明显,整体上,田间道比例提高幅度较大,但生产路在整个道路体系中所占的比例仍最大,其次为田间道,等级公路最少。建设前,样区Ⅰ、样区Ⅱ、样区Ⅲ、样区Ⅳ、样区Ⅴ的等级公路：田间道：生产路的比例依次分别为11：15：74,0：31：69,9：12：79,3：17：80,8：28：64。建设后,样区Ⅰ、样区Ⅱ、样区Ⅲ、样区Ⅳ、样区Ⅴ的等级公路：田间道：生产路的比例依次分别为9：17：74,0：27：73,7：23：70,3：16：81,6：25：69。
从农村道路网络指数来看,网络密度d指数、网络闭合度α指数、线点率β指数以及网络连接度γ指数均有所提高,而成本比C指数则有一定程度降低。建设前,网络闭合度α指数变化范围为0.126～0.361,线点率β指数变化范围为1.242～1.681,连接度γ指数变化范围为0.419～0.577,成本比C指数变化范围为0.9908～0.9971；建设后,道路网络的α指数变化范围为0.312～0.370,β指数变化范围为1.614～1.707,γ指数变化范围为0.542～0.582,C指数变化范围为0.9913～0.9956。同时,在西南丘陵山区,随着道路的扩展,道路网络的节点数和廊道数也呈增加趋势,这种增加为直线关系,而且不同区域节点数和廊道数差异较大,造成区域之间道路密度存在一定差异。此外,道路密度与网络闭合度α指数、线点率β指数、网络连接度γ指数呈正相关关系,而与C指数呈显著负相关,即随着道路网络的扩展,成本比逐渐降低。Moran指数进一步表明：建设前,样区Ⅴ的道路密度较分散,而样区Ⅰ、Ⅱ、Ⅲ和Ⅳ均是相对聚集,建设后,样区Ⅰ、Ⅲ和Ⅴ道路密度显著增加,而样区Ⅱ和Ⅳ道路密度增加的幅度不大,造成这种差异的原因在于样区Ⅱ和Ⅳ地形相对陡峭,而样区Ⅰ、Ⅲ和Ⅴ的地势相对较平坦。因此,农村道路作为一个农村景观廊道或农田物质流、价值流通道,可用网络结构分析进行表达(评价),并实现农村道路体系网络优化。
(4)农村道路体系景观效应
在类型水平上,农村道路对周边土地利用格局的干扰程度以道路为中心线,向两侧大致呈现逐渐衰减的变化规律。田间道主要穿过水田、早地及居民点人类活动最频繁的区域,对三者的破碎化干扰最显著。田间道25m以内对景观连接度干扰最明显,25m以外干扰度逐渐衰弱。田间道10m以内对土地利用干扰强度最剧烈,10-25m以内干扰强度较为剧烈,25m以外随着距离的增加,干扰程度逐渐衰减。0-25m干扰带内田间道对土地利用类型的分割破碎程度大致呈现此规律：早地>水田>居民点>水域>林地。25m-250m干扰带内,水田>旱地>居民点>水域>林地。生产路2.5m以内对土地利用格局干扰强度随距离增加反而增强,2.5-10m以内干扰强度随距离增加减小且干扰最剧烈,10-30m以内干扰强度相当,30m以外随着距离的增加,干扰程度逐渐衰减。0-20m干扰带内生产路对土地利用类型的分割破碎程度大致呈现此规律：水田>旱地>居民点>水域>林地。20m-120m干扰带内,旱地>水田>居民点>水域>林地。
在景观水平上,田间道对周边土地利用景观格局的干扰程度基本也以田间道为中心线,向两侧大致呈现逐渐衰减的变化规律,但生产路向两侧大致呈现先增强再逐渐衰减的变化规律。田间道5m以内对土地利用景观干扰强度最强,5m以外随着距离的增加,干扰程度逐渐衰减乃至不明显。田间道建设后,除样区Ⅳ在0～10m内景观破碎情况略有加剧外,其他四个样区在10～250m内基本不变,在0～10m内基本得到改善或缓解；景观边界的复杂弯曲程度在一定程度上均略有提高,类型景观形状规则化程度有所增加,样区优势土地利用景观类型相邻斑块的连续性总体上有所提高,主要土地利用景观类型优势地位未受威胁甚至有所提高。生产路5m以内对土地利用景观干扰强度随距离增加而增强,2.5～5m以内干扰强度随距离增加干扰最为剧烈,5～10m以内干扰强度较大,10～30m以外随着距离的增加,干扰程度逐渐衰减乃至不明显。生产路建设后,景观破碎度在0～30m内得到改善,在30～120m内基本不变外,但其景观边界的复杂弯曲程度在一定程度上略有提高,类型景观形状规则化程度稍有降低。因此,农村道路作为一种土地利用(景观)类型,它的重建能优化农村局地土地利用(景观)格局,实现土地高效利用。
综上所述,本文主要以生产路、田间道的布局与结构设计阐明了西南丘陵山区农村道路等级结构体系的构建思路；从廊道结构指数、网络结构指数、空间自相关Moran指数三个层面分析了西南丘陵山区农村道路体系构建前后的网络特征；在这两者的基础上探讨了农村道路的形成和发展对周边土地利用格局的影响,从而揭示了西南丘陵山区农村道路体系构建前后的景观效应。但事实上道路的景观效应不仅体现在道路对周边土地利用的影响,还包括对区域交通、人类活动、社区结构和组织、生态系统及功能演替等的影响,而且这种效应在道路构建的整个过程中都发生着作用。因此,需从多角度加强农村道路体系构建过程中人类活动、社区结构和组织、社会经济发展的动态研究。
As one of the key rural infrastructure, rural roads has got rapid expansion recently basing on the comprehensive land consolidation, the new countryside construction and urban and rural harmonious development. Current researches focus on high-grade road system in the large geomorphic unit, like the gathering and radiation of logistics and the exchange of information coming from coherent road network such as highways, railways, state (province) road or county road, and "channel - blocking " effect driving on heterogeneity and diversity of landscape use and land cover in large geomorphic unit and its impact on ecosystems. Low-grade rural roads are concentrated in the layout and evaluation of road network, design and cost control of road construction, engineering construction, quality control and maintenance management, surface drainage, slope erosion and road erosion control and so on. However, the rural roads distributed widely in the Hilly-mountainous Region of Southwestern China are restricted not only by human economic activities, but also by natural conditions. Its construction and operation provide a protection for social development and a promoting economic development, while cause a division, disturbance, destruction and degradation of natural landscape and ecosystems and so on. Considering this, picking 14 administrative villages from Sichuan Province(areaⅠ), Guizhou Province(areaⅡ) and Chongqing City(areaⅢ,ⅣandⅤ) as 5 study areas, this paper analyzed the type and function of rural roads in different geographical environment combining with socio-economic levels including topography, hydrogeology, climate, soil, vegetation, rural population, cultivated land, per capita arable land, infrastructure, agricultural production conditions, farming systems and the socio-economic.
It also cleared the requirement for rural roads according to the economic development status and future development trend in the Hilly-mountainous Region of Southwestern China. And it researched the engineering technology of rural roads such as surface and subgrade combining with the usage of local agricultural machinery and characteristics of common building materials. Moreover, it built the rural road system in Hilly-mountainous Region of Southwestern, and analyzed features of the rural road network systems and its landscape effect so that provided a support on theory and technical to rural road system layout and design in Hilly-mountainous Region of Southwestern China.
(1) The layout of rural road
Rural roads can be divided into field roads and production roads by function and road pavement width. Field road is a road contacting rural residential area with piece of paddy fields, which mainly services for cargo transporting, transferring of operating machinery to field and fueling the machine, adding water, adding seed and other production operation. It is better to adopt orthogonal when field road intersect to facilitate turning of farm machinery. Field roads should be laid along the short edge of the piece of paddy field, whereas it can be laid in the middle of field operation area in the dry farming region, along the long side of the piece of paddy field so that farm machinery can enter the work area on both sides to reduce the blank line. It should be arranged according to specific terrain in the terrace area shall, laid by the method of walking along the edge of the trench. Field road is usually set beside the gutter, deep in ditch or on the mountain ridge. It presents a bias shape when the mountains are low and slopes are even; it presents an "S" shape or a spiral shape winding up the mountain when the mountains are high and slopes are steep. Production road is the kind of road to link each piece of paddy fields for field production operations and mainly services for manual field work and harvesting agricultural products. It should be criss-cross laid to form a network with field road. It often locates in the long side of the piece of paddy field and presents different ways in dry lands and paddy fields. One horizontal production road in dry lands farmland separates another from 40 to 200 meters. It can be laid combining with gallet bank in areas gallet is widely spread to save space. Vertical production roads are often arranged on the hilly ridges and one separates another from 200 to 500 meters according to the length of the field surface. If the production roads and ditches are not conducive to drain off water or traffic when combined settings, they will be arranged separately. Production roads in paddy can be set outside the agricultural ditch and directly connected with paddy fields. Horizontal production road can be arranged an interval of 100 to 300m, vertical one can be arranged an interval of 200 to 500m; It should avoid areas like erosion around the depressions, cave development zones and large fault fracture zone in soluble limestone regimen which with complex geological conditions. Rural roads should be laid combining topography conditions and production methods as far as possible. What is more, field roads can be laid combining branch canal and lateral canal, production roads can be laid with field ditch. In sum, the layout rural roads in the Hilly-mountainous Region of Southwestern China should not only consider the distribution of rural settlements, facilities of irrigation and settings of farming plots, but also harmonize with the natural environmental conditions, agricultural and human landscape.
(2) Engineering design of rural roads
Rural road surface is designed above the original ground surface about 20 to 30cm in purple rock area, and the pavement bed course is built by hand placed stones of 20cm. The foundation course is a stable layer of gravel mud of 10 to 15cm, and road surface is covered by 15 to 20cm thick cement concrete of C25～C30. The soil base in this area has a high intensity so the subgrade can be compacted directly with a degree of compaction above 90%. The width of subgrade is 4.5 to 5.0m, slope ratio is 1:1.5. Taking into account the long rainfall period and large rainwater harvesting area in the region, the ditch can be laid at the runoff side of the subgrade, the width of it is 0.25 to 0.30m, and the net depth of it is 0.3 to 0.4m. The trench wall of it is built by cement mortar boulder strip of M10-M15 or mortar block stone, and the bottom is paved by cement concrete of C15-C20 with 8～10cm. To ensure the stability of the subgrade, the road shoulder is adopted on the other side of the field road using stone curb, precast concrete or soil; Due to the frequent water and soil erosion from both sides of the hill in the soluble limestone region, the subgrade and pavement in this region are designed thicker than the purple soil region, and exceed the ground of 30 to 40cm. The pavement bed course is built by hand placed stones of 20cm, and the foundation course is a stable layer of gravel mud of 15cm, and road surface is covered by 18 to 20cm thick cement concrete of C30. Clear width of the road is 3.5 to 4.5m with cross slope of 0.3% to 0.5%. The flat curve of field road has a radius (turning radius) not less than 15m, on special difficulties not less than 10m, and its length cannot be less than 15m. When the radius of flat curve is equal to or less than 150m, the curve should be set ultra-high and the inside of the curve should be widened. Meantime the ultra-high eased segment not less than 10m should be set at both ends of a flat curve. The ultra-high cross slope value does not exceed 8% and not more than 6% in snow frozen area. The maximum longitudinal slope of field road should take 6% to 8%. Under special circumstances, it's not more than 11% in hilly area, not more than 13% in the mountain area, and not more than 8% in an altitude of 2000m above areas or freezing cold region. Whether in purple rock area or soluble limestone area, the passing bay should be set in the appropriate distance when the road surface width of field road is less than 4.0m, Passing bay should be located in vantage point, and make the driver can see the approaching vehicles from two adjacent passing bay. The section of pavement setting the passing bay has a road surface width of not less than 6.5m, the interval should be of 300 to 600m, the effective length shall be 15 to 25m; Production road in purple rock area should adopt rubble, stone block cushion, and its subgrade width should be 0.6 to 2.7 m. The width of the road is designed from 0.6 to 2.5m. Soil can be used to compact subgrade in free water and erosion areas, and the subgrade of production road should be higher than the road surface 0.1 to 0.2m. The grouting stone subgrade should be adopted in soluble limestone area, above the field surface 0.2 to 0.5m. The pavement of production road can be produced by cast-in-situ concrete, precast concrete board, green flag and other materials. The concrete road surface should be of 5 to 20cm thick, the precast concrete board and flag should be of 6～15cm, and other materials are desirable of 8～20cm. Agricultural bridge can be arranged where field road and production road crossing ditches or gully which falls into for field road and for pedestrian. Its structural design safety level is not less than the third grade. Types of agriculture bridges can be the beam type and the vault type, and building materials usually are brick, stone, concrete and reinforced concrete etc. Culvert should be built under the canal, road or the ground when the road crossing the canal. There should be a certain distance of 20 to 30cm away from the top of the culvert to the subgrade. Culvert water direction should be orthogonal with fill ditches on roof or roads, in accordance with the original direction. The culvert can be made by concrete or reinforced concrete pipe, and the form of it can be round, box, cover type and vault type etc. In a word, the engineering design of rural roads in Hilly-mountainous Region of Southwestern China should consider the geological topography, hydrology, land use and soil characteristics of the road sections passing, meanwhile make use of local materials to reduce costs.
(3) Characteristics of the rural road network system
On the one hand, the differences of natural conditions and socio-economic in these study areas intensified the differences of focus on building in regional road system. On the other hand, the whole road systems had become more comprehensive, and the differences in the network characteristics had narrowed. Like the index of view from the corridor, the total length and density of rural roads in all cease areas had increased. Before building, total length of the road in these villages ranged from 6.73km to 76.36 km, the longest was 11.4 times longer than the shortest. The network density of road ranged from 38.18 m/hm2 to 149.6 m/hm2, and the biggest was 11.4 times bigger than the smallest. After building, the length ranged from 7.88 km to 82.15 km and the gap narrowed to 10.4 times; the density ranged from 65.87 m/hm2 to 159.6 m/hm2 and the gap was only 2.4 times. In addition, there was a remarkable structural change in the type of road consisting systems. Although increased greatly the proportion of field road, the production of road still occupied the main parts in the entire road system. Before building, the ratio of high road, Field Road and production ratio in areaⅠ, areaⅡ, areaⅢ, areaⅣ, areaⅤwere 11:15:74,0:31:69,9:12:79,3:17: 80,8:28:64 respectively. After building, those were 9:17:74,0:27:73,7:23:70,3: 16:81,6:25:69.
Considering the index of the rural road network, the network density index (d), the network closure index (α), the line point rate (β) and the network connectivity index (γ) were higher, while costs rate index (C) reduced in some extent. Before building, a ranged from 0.126 to 0.361:βranged from 1.242 to 1.681:y ranged from 0.419 to 0.577:C ranged from 0.9908 to 0.9971. After building, a index ranged from 0.312 to 0.370, (3 index ranged from 1.614 to 1.707, y index ranged from 0.542 to 0.582, C ranged from 0.9913 to 0.9956.
Meanwhile, in the Hilly-mountainous Region of Southwestern, there were an increasing trend in the number of nodes and corridors of the road network with the road expansion. The differences of road density in these regions were attributed to the differences of the number of nodes and corridors between the different regions. In addition, a, (3, y were positively correlated whereas were significantly negatively correlated with C, that is, the cost ratio decreased with the expansion of road network. Moran index further indicated that:before the construction, the road density inⅤwas decentralized, whereas they were relatively gathered inⅠ,Ⅱ,ⅢandⅣ. After the construction, the road density inⅠ,ⅢandⅤincreased significantly, while they increased slightly inⅡandⅣ. The reason for this is that the terrain ofⅡandⅥis relatively steep, while it is relatively flat inⅠ,ⅢandⅤ. So we found that:as a rural agricultural landscape corridor or channel for material flow and value flow, the rural roads can be evaluated by the network structure analysis, moreover by it can attain the rural road system network optimization.
(4) The landscape effect of rural road system
According the type, using the road as centerline, the degree of interference of rural roads on the surrounding land use pattern generally shows a gradual decay to both sides of the road. Across the paddy field, dry land and the regions which are the human settlements in, the field road make the most significant interference with the fragmentation of those regions. The results indicated:it made the most significant degree of interference with landscape connectivity within 25m, and the interference gradually weakened beyond 25m. Meantime, it brought severe interference with land use disturbance in 10-25m and the hugest one was within 10m. Exceeding 25m, the degree of interference gradually decayed away as the distance increased. In 0-25m interference band, degree of fragmentation of the land-use types from field road showed:dry land> paddy> settlement water> woodland, and in 25m-250m band showed:paddy field> dry> settlement> water> woodland. The intensity of interference pattern of land use from production path increased with distance adding within 2.5m, while it decreased with distance adding and the severest disturbance happened within 2.5-10m. It changed less in 10-30m and gradual decayed over 30m. In 0-20m interference band, degree of fragmentation of the land-use types from production road showed:paddy fields> dry> settlement> water> woodland, and in 25m-250m band showed:dry land> paddy> settlement> water> woodland.
According the landscape, using the road as centerline, the degree of interference of field roads on the surrounding landscape pattern also shows a gradual decay to both sides of the road, while interference of the production shows an increasing trend at first and then gradually decayed. The results indicated:the strongest intensity of disturbance on land use landscape from field road was in 5m, and it decreased with distance increasing beyond 5m. After the construction of field road, except IV which had a slightly increased of landscape fragmentation in the 0-10m, the landscape fragmentation in other four regions were improved or mitigated, they were almost same in the 10-250m. The complex bending degree of landscape border raised slight in a certain extent, and the degree of regular shape of the landscape types increased. The continuity of adjacent plots of preponderant land use in study areas increased overall, and the dominant landscape types was not threatened or even increased. The disturbance on landscape from production road increased with distance adding within 5 m, and the most severe of interference came from 2.5 to 5m band. In the 5-10m band, the disturbance was still large. Over 10m, however, the degree of interference gradually decayed away as the distance increased. The degree of the landscape fragmentation within the 0-30m was improved due to the construction of production road. Although it kept same within 30-120m, the complexity of landscape boundaries rose slightly while the degree of regular shape of the landscape types reduced slightly. Therefore, as a landscape type, the rural roads can optimize the reconstruction of local rural land use so that the efficient use can be achieved.
In summary, this paper demonstrated the idea about the hierarchy system of rural roads in Hilly-mountainous Region of Southwestern China by the layout and the structural design of production road and field road. It analyzed features of the network system of rural road in Hilly-mountainous Region of Southwestern China pre and post construction by indexes of corridor structure, network structure and the spatial autocorrelation (Moran). Basing on those, it discussed what influence on the surrounding land use pattern from the formation and development of rural roads. Thus it revealed the landscape effect pre and post construction of the rural road system in Hilly-mountainous Region of Southwestern. However, the landscape effect from road is not just in the impact on the surrounding land use, it also includes impact on regional transportation, human activity, community structure and organization and function and succession of ecosystems and so on. What is more, this effect works in the whole process of road building. Therefore, it is necessary to strengthen the research on human activity, community structure and organization, the dynamics of social and economic development which correlate with construction process of rural road system from multi-angle.
(1)农村道路布局
农村道路按功能和路面宽度可分为田间道和生产路两级。田间道应沿田块的短边布设,在旱作地区,田间道也可布设在作业区的中间,沿田块的长边布设,使耕作机械两边均可进入工作小区以减少空行。在梯田区布置田间道应按照具体地形,采取通梁联峁,沿沟走边的方法布设。田间道多设置在沟边、沟底或山峁的脊梁上。山低坡缓,田间道呈斜线形；山高坡陡,田间道可呈“S”形、“之”字形或螺旋形迂回上山；生产路宜纵横交错布置,因地制宜地与田间道形成网状,设在田块的长边,并分旱地区和水田区采取不同的方式布置。旱地横向生产路为40～200m,布置一条生产路。在石坎较多的地区可与石坎结合设置,以节约用地。纵向生产路多布置在丘陵山地的脊部,根据田面长度,一般200～500m布置一条。如果生产路与沟渠组合设置不利于排水或不利于通行时,应分开布置。水田生产路可设置在农沟外侧与田块直接连接。横向生产路可间隔100～300m布置一条,纵向生长路可间隔200～500m布置一条；与紫色岩溶区相比,石灰岩溶区的地质条件更具有复杂性,应绕避溶蚀洼地、溶洞发育区和大断层破碎带。农村道路应尽可能地结合地形地貌条件及生产方式进行布置,体现因地制宜原则。田间道可与支、斗渠沟结合布置,生产路可与农渠沟结合布置。因此,西南丘陵山区农村道路布局不仅要充分考虑农村居民点分布、农田水利设施和耕作田块设置等,还应顺应自然环境条件、融于农业自然人文景观。
(2)农村道路工程设计
紫色岩区路面设计高出原地面约20～30cm,路面垫层采用20cm厚手摆片石,路面基层为10～15cm泥结碎石稳定层,路面面层采用15～20cm厚C25～C30水泥混凝土进行铺设。该区域土基强度较高,可采用原土路基夯实,压实度在90%以上。路基的宽度为4.5～5.0m,边坡采用1：1.5。同时考虑到本区域降雨期较长,集雨面积较大,可在路基来水一侧布设边沟,沟底宽0.25～0.30m、净深0.3～0.4m,沟壁采用M10～M15水泥砂浆砌毛条石或浆砌块石,沟底铺设8～10cm厚C15～C20水泥混凝土。为了保证路基的稳定,设计在田间道的另一侧利用条石修建条石路肩、预制混凝土或土质路肩；石灰岩溶地区常常遭受两侧山坡水土的冲蚀,三水转化快,因此,路基和路面设计比紫色土区厚,高出原地面约30～40cm。路面垫层采用20cm厚手摆片石,路面基层为15cm泥结碎石稳定层,路面面层采用18～20cm厚C30水泥混凝土进行铺设。路面宽度净宽为3.5～4.5m,横坡为0.3%～0.5%；田间道的平曲线半径(转弯半径)应不小于15m,特殊困难地段不得小于10m,平曲线长度不得少于15m。当平曲线半径等于或小于150m时,应在曲线上设置超高,在曲线内侧加宽,并在平曲线两端各设置一段不少于10m的超高缓和段,超高横坡度最大值不超过8%,积雪冰冻地区不超过6%。田间道最大纵坡宜取6%～8%,特殊情况下,丘陵地区不宜大于11%,山区不宜大于13%；在海拔2000m以上或严寒冰冻地区不宜大于8%。无论是紫色岩区还是石灰岩溶区,当田间道路面宽度小于4.0m时,均应在适当距离内设置错车道。错车道应设在有利地点,并使驾驶员能看到相邻两错车道间驶来的车辆。设置错车道路段的路面宽度不应小于6.5m,间隔宜为300～600m,有效长度宜为15～25m；紫色岩区生产路宜采用片石、块石垫层,路基宽宜为0.6～2.7m,路面宽度设计为0.6～2.5m。无积水和流水冲刷的地区可采用夯实素土路基,生产路路基宜高于路面0.1～0.2m。石灰岩溶区宜采用浆砌石质路基,高出田面高程0.2～0.5m。生产路路面均可采用砼现浇、预制砼板、青石板等材料,砼路面厚度宜为5～20cm,预制砼板、石板宜为6～15cm,其他材料宜为8～20cm。田间道、生产路跨越沟渠或溪沟处可布置农桥,农桥分为田间道桥和人行便桥。结构设计安全等级不低于三级。农桥的结构形式可采用梁式和拱式。建筑材料可用砖、石、混凝土及钢筋混凝土等。道路穿越渠道时,宜在渠、路下或地下设置涵洞。涵洞的顶端距路基要有一定的距离为20～30cm。涵洞水流的方向,应与洞顶填方沟渠或道路正交,与原水道的方向一致。涵洞的形式可采用圆形、箱形、盖板式和拱式等,选用混凝土或钢筋混凝土管。因此,西南丘陵山区农村道路工程设计,除充分考虑道路所经路段的地质地貌、水文、土地利用类型和土壤特性外,还应就地取材,降低建造成本。
(3)农村道路体系网络特征
五个样区自然条件与社会经济等差异加剧了区域各级道路体系构建重点的差异,但整体上道路体系均更加趋于健全和完善,网络特征存在一定差异但有所缩小。从廊道指数来看,五个样区农村道路建设后较建设前的总长度、密度均有不同程度增加。建设前,各行政村道路总长度变化范围为6.73km～76.36 km,相差11.4倍,建设后其为7.88km～82.15km,变化范围缩小至10.4倍；建设前,道路网络密度为38.18 m/hm2～149.6 m/hm2,相差近4倍,建设后其为65.87 m/hm2～159.6 m/hm2,相差仅2.4倍。此外,五个样区农村道路建设前后道路类型组合的结构变化也较为明显,整体上,田间道比例提高幅度较大,但生产路在整个道路体系中所占的比例仍最大,其次为田间道,等级公路最少。建设前,样区Ⅰ、样区Ⅱ、样区Ⅲ、样区Ⅳ、样区Ⅴ的等级公路：田间道：生产路的比例依次分别为11：15：74,0：31：69,9：12：79,3：17：80,8：28：64。建设后,样区Ⅰ、样区Ⅱ、样区Ⅲ、样区Ⅳ、样区Ⅴ的等级公路：田间道：生产路的比例依次分别为9：17：74,0：27：73,7：23：70,3：16：81,6：25：69。
从农村道路网络指数来看,网络密度d指数、网络闭合度α指数、线点率β指数以及网络连接度γ指数均有所提高,而成本比C指数则有一定程度降低。建设前,网络闭合度α指数变化范围为0.126～0.361,线点率β指数变化范围为1.242～1.681,连接度γ指数变化范围为0.419～0.577,成本比C指数变化范围为0.9908～0.9971；建设后,道路网络的α指数变化范围为0.312～0.370,β指数变化范围为1.614～1.707,γ指数变化范围为0.542～0.582,C指数变化范围为0.9913～0.9956。同时,在西南丘陵山区,随着道路的扩展,道路网络的节点数和廊道数也呈增加趋势,这种增加为直线关系,而且不同区域节点数和廊道数差异较大,造成区域之间道路密度存在一定差异。此外,道路密度与网络闭合度α指数、线点率β指数、网络连接度γ指数呈正相关关系,而与C指数呈显著负相关,即随着道路网络的扩展,成本比逐渐降低。Moran指数进一步表明：建设前,样区Ⅴ的道路密度较分散,而样区Ⅰ、Ⅱ、Ⅲ和Ⅳ均是相对聚集,建设后,样区Ⅰ、Ⅲ和Ⅴ道路密度显著增加,而样区Ⅱ和Ⅳ道路密度增加的幅度不大,造成这种差异的原因在于样区Ⅱ和Ⅳ地形相对陡峭,而样区Ⅰ、Ⅲ和Ⅴ的地势相对较平坦。因此,农村道路作为一个农村景观廊道或农田物质流、价值流通道,可用网络结构分析进行表达(评价),并实现农村道路体系网络优化。
(4)农村道路体系景观效应
在类型水平上,农村道路对周边土地利用格局的干扰程度以道路为中心线,向两侧大致呈现逐渐衰减的变化规律。田间道主要穿过水田、早地及居民点人类活动最频繁的区域,对三者的破碎化干扰最显著。田间道25m以内对景观连接度干扰最明显,25m以外干扰度逐渐衰弱。田间道10m以内对土地利用干扰强度最剧烈,10-25m以内干扰强度较为剧烈,25m以外随着距离的增加,干扰程度逐渐衰减。0-25m干扰带内田间道对土地利用类型的分割破碎程度大致呈现此规律：早地>水田>居民点>水域>林地。25m-250m干扰带内,水田>旱地>居民点>水域>林地。生产路2.5m以内对土地利用格局干扰强度随距离增加反而增强,2.5-10m以内干扰强度随距离增加减小且干扰最剧烈,10-30m以内干扰强度相当,30m以外随着距离的增加,干扰程度逐渐衰减。0-20m干扰带内生产路对土地利用类型的分割破碎程度大致呈现此规律：水田>旱地>居民点>水域>林地。20m-120m干扰带内,旱地>水田>居民点>水域>林地。
在景观水平上,田间道对周边土地利用景观格局的干扰程度基本也以田间道为中心线,向两侧大致呈现逐渐衰减的变化规律,但生产路向两侧大致呈现先增强再逐渐衰减的变化规律。田间道5m以内对土地利用景观干扰强度最强,5m以外随着距离的增加,干扰程度逐渐衰减乃至不明显。田间道建设后,除样区Ⅳ在0～10m内景观破碎情况略有加剧外,其他四个样区在10～250m内基本不变,在0～10m内基本得到改善或缓解；景观边界的复杂弯曲程度在一定程度上均略有提高,类型景观形状规则化程度有所增加,样区优势土地利用景观类型相邻斑块的连续性总体上有所提高,主要土地利用景观类型优势地位未受威胁甚至有所提高。生产路5m以内对土地利用景观干扰强度随距离增加而增强,2.5～5m以内干扰强度随距离增加干扰最为剧烈,5～10m以内干扰强度较大,10～30m以外随着距离的增加,干扰程度逐渐衰减乃至不明显。生产路建设后,景观破碎度在0～30m内得到改善,在30～120m内基本不变外,但其景观边界的复杂弯曲程度在一定程度上略有提高,类型景观形状规则化程度稍有降低。因此,农村道路作为一种土地利用(景观)类型,它的重建能优化农村局地土地利用(景观)格局,实现土地高效利用。
综上所述,本文主要以生产路、田间道的布局与结构设计阐明了西南丘陵山区农村道路等级结构体系的构建思路；从廊道结构指数、网络结构指数、空间自相关Moran指数三个层面分析了西南丘陵山区农村道路体系构建前后的网络特征；在这两者的基础上探讨了农村道路的形成和发展对周边土地利用格局的影响,从而揭示了西南丘陵山区农村道路体系构建前后的景观效应。但事实上道路的景观效应不仅体现在道路对周边土地利用的影响,还包括对区域交通、人类活动、社区结构和组织、生态系统及功能演替等的影响,而且这种效应在道路构建的整个过程中都发生着作用。因此,需从多角度加强农村道路体系构建过程中人类活动、社区结构和组织、社会经济发展的动态研究。
As one of the key rural infrastructure, rural roads has got rapid expansion recently basing on the comprehensive land consolidation, the new countryside construction and urban and rural harmonious development. Current researches focus on high-grade road system in the large geomorphic unit, like the gathering and radiation of logistics and the exchange of information coming from coherent road network such as highways, railways, state (province) road or county road, and "channel - blocking " effect driving on heterogeneity and diversity of landscape use and land cover in large geomorphic unit and its impact on ecosystems. Low-grade rural roads are concentrated in the layout and evaluation of road network, design and cost control of road construction, engineering construction, quality control and maintenance management, surface drainage, slope erosion and road erosion control and so on. However, the rural roads distributed widely in the Hilly-mountainous Region of Southwestern China are restricted not only by human economic activities, but also by natural conditions. Its construction and operation provide a protection for social development and a promoting economic development, while cause a division, disturbance, destruction and degradation of natural landscape and ecosystems and so on. Considering this, picking 14 administrative villages from Sichuan Province(areaⅠ), Guizhou Province(areaⅡ) and Chongqing City(areaⅢ,ⅣandⅤ) as 5 study areas, this paper analyzed the type and function of rural roads in different geographical environment combining with socio-economic levels including topography, hydrogeology, climate, soil, vegetation, rural population, cultivated land, per capita arable land, infrastructure, agricultural production conditions, farming systems and the socio-economic.
It also cleared the requirement for rural roads according to the economic development status and future development trend in the Hilly-mountainous Region of Southwestern China. And it researched the engineering technology of rural roads such as surface and subgrade combining with the usage of local agricultural machinery and characteristics of common building materials. Moreover, it built the rural road system in Hilly-mountainous Region of Southwestern, and analyzed features of the rural road network systems and its landscape effect so that provided a support on theory and technical to rural road system layout and design in Hilly-mountainous Region of Southwestern China.
(1) The layout of rural road
Rural roads can be divided into field roads and production roads by function and road pavement width. Field road is a road contacting rural residential area with piece of paddy fields, which mainly services for cargo transporting, transferring of operating machinery to field and fueling the machine, adding water, adding seed and other production operation. It is better to adopt orthogonal when field road intersect to facilitate turning of farm machinery. Field roads should be laid along the short edge of the piece of paddy field, whereas it can be laid in the middle of field operation area in the dry farming region, along the long side of the piece of paddy field so that farm machinery can enter the work area on both sides to reduce the blank line. It should be arranged according to specific terrain in the terrace area shall, laid by the method of walking along the edge of the trench. Field road is usually set beside the gutter, deep in ditch or on the mountain ridge. It presents a bias shape when the mountains are low and slopes are even; it presents an "S" shape or a spiral shape winding up the mountain when the mountains are high and slopes are steep. Production road is the kind of road to link each piece of paddy fields for field production operations and mainly services for manual field work and harvesting agricultural products. It should be criss-cross laid to form a network with field road. It often locates in the long side of the piece of paddy field and presents different ways in dry lands and paddy fields. One horizontal production road in dry lands farmland separates another from 40 to 200 meters. It can be laid combining with gallet bank in areas gallet is widely spread to save space. Vertical production roads are often arranged on the hilly ridges and one separates another from 200 to 500 meters according to the length of the field surface. If the production roads and ditches are not conducive to drain off water or traffic when combined settings, they will be arranged separately. Production roads in paddy can be set outside the agricultural ditch and directly connected with paddy fields. Horizontal production road can be arranged an interval of 100 to 300m, vertical one can be arranged an interval of 200 to 500m; It should avoid areas like erosion around the depressions, cave development zones and large fault fracture zone in soluble limestone regimen which with complex geological conditions. Rural roads should be laid combining topography conditions and production methods as far as possible. What is more, field roads can be laid combining branch canal and lateral canal, production roads can be laid with field ditch. In sum, the layout rural roads in the Hilly-mountainous Region of Southwestern China should not only consider the distribution of rural settlements, facilities of irrigation and settings of farming plots, but also harmonize with the natural environmental conditions, agricultural and human landscape.
(2) Engineering design of rural roads
Rural road surface is designed above the original ground surface about 20 to 30cm in purple rock area, and the pavement bed course is built by hand placed stones of 20cm. The foundation course is a stable layer of gravel mud of 10 to 15cm, and road surface is covered by 15 to 20cm thick cement concrete of C25～C30. The soil base in this area has a high intensity so the subgrade can be compacted directly with a degree of compaction above 90%. The width of subgrade is 4.5 to 5.0m, slope ratio is 1:1.5. Taking into account the long rainfall period and large rainwater harvesting area in the region, the ditch can be laid at the runoff side of the subgrade, the width of it is 0.25 to 0.30m, and the net depth of it is 0.3 to 0.4m. The trench wall of it is built by cement mortar boulder strip of M10-M15 or mortar block stone, and the bottom is paved by cement concrete of C15-C20 with 8～10cm. To ensure the stability of the subgrade, the road shoulder is adopted on the other side of the field road using stone curb, precast concrete or soil; Due to the frequent water and soil erosion from both sides of the hill in the soluble limestone region, the subgrade and pavement in this region are designed thicker than the purple soil region, and exceed the ground of 30 to 40cm. The pavement bed course is built by hand placed stones of 20cm, and the foundation course is a stable layer of gravel mud of 15cm, and road surface is covered by 18 to 20cm thick cement concrete of C30. Clear width of the road is 3.5 to 4.5m with cross slope of 0.3% to 0.5%. The flat curve of field road has a radius (turning radius) not less than 15m, on special difficulties not less than 10m, and its length cannot be less than 15m. When the radius of flat curve is equal to or less than 150m, the curve should be set ultra-high and the inside of the curve should be widened. Meantime the ultra-high eased segment not less than 10m should be set at both ends of a flat curve. The ultra-high cross slope value does not exceed 8% and not more than 6% in snow frozen area. The maximum longitudinal slope of field road should take 6% to 8%. Under special circumstances, it's not more than 11% in hilly area, not more than 13% in the mountain area, and not more than 8% in an altitude of 2000m above areas or freezing cold region. Whether in purple rock area or soluble limestone area, the passing bay should be set in the appropriate distance when the road surface width of field road is less than 4.0m, Passing bay should be located in vantage point, and make the driver can see the approaching vehicles from two adjacent passing bay. The section of pavement setting the passing bay has a road surface width of not less than 6.5m, the interval should be of 300 to 600m, the effective length shall be 15 to 25m; Production road in purple rock area should adopt rubble, stone block cushion, and its subgrade width should be 0.6 to 2.7 m. The width of the road is designed from 0.6 to 2.5m. Soil can be used to compact subgrade in free water and erosion areas, and the subgrade of production road should be higher than the road surface 0.1 to 0.2m. The grouting stone subgrade should be adopted in soluble limestone area, above the field surface 0.2 to 0.5m. The pavement of production road can be produced by cast-in-situ concrete, precast concrete board, green flag and other materials. The concrete road surface should be of 5 to 20cm thick, the precast concrete board and flag should be of 6～15cm, and other materials are desirable of 8～20cm. Agricultural bridge can be arranged where field road and production road crossing ditches or gully which falls into for field road and for pedestrian. Its structural design safety level is not less than the third grade. Types of agriculture bridges can be the beam type and the vault type, and building materials usually are brick, stone, concrete and reinforced concrete etc. Culvert should be built under the canal, road or the ground when the road crossing the canal. There should be a certain distance of 20 to 30cm away from the top of the culvert to the subgrade. Culvert water direction should be orthogonal with fill ditches on roof or roads, in accordance with the original direction. The culvert can be made by concrete or reinforced concrete pipe, and the form of it can be round, box, cover type and vault type etc. In a word, the engineering design of rural roads in Hilly-mountainous Region of Southwestern China should consider the geological topography, hydrology, land use and soil characteristics of the road sections passing, meanwhile make use of local materials to reduce costs.
(3) Characteristics of the rural road network system
On the one hand, the differences of natural conditions and socio-economic in these study areas intensified the differences of focus on building in regional road system. On the other hand, the whole road systems had become more comprehensive, and the differences in the network characteristics had narrowed. Like the index of view from the corridor, the total length and density of rural roads in all cease areas had increased. Before building, total length of the road in these villages ranged from 6.73km to 76.36 km, the longest was 11.4 times longer than the shortest. The network density of road ranged from 38.18 m/hm2 to 149.6 m/hm2, and the biggest was 11.4 times bigger than the smallest. After building, the length ranged from 7.88 km to 82.15 km and the gap narrowed to 10.4 times; the density ranged from 65.87 m/hm2 to 159.6 m/hm2 and the gap was only 2.4 times. In addition, there was a remarkable structural change in the type of road consisting systems. Although increased greatly the proportion of field road, the production of road still occupied the main parts in the entire road system. Before building, the ratio of high road, Field Road and production ratio in areaⅠ, areaⅡ, areaⅢ, areaⅣ, areaⅤwere 11:15:74,0:31:69,9:12:79,3:17: 80,8:28:64 respectively. After building, those were 9:17:74,0:27:73,7:23:70,3: 16:81,6:25:69.
Considering the index of the rural road network, the network density index (d), the network closure index (α), the line point rate (β) and the network connectivity index (γ) were higher, while costs rate index (C) reduced in some extent. Before building, a ranged from 0.126 to 0.361:βranged from 1.242 to 1.681:y ranged from 0.419 to 0.577:C ranged from 0.9908 to 0.9971. After building, a index ranged from 0.312 to 0.370, (3 index ranged from 1.614 to 1.707, y index ranged from 0.542 to 0.582, C ranged from 0.9913 to 0.9956.
Meanwhile, in the Hilly-mountainous Region of Southwestern, there were an increasing trend in the number of nodes and corridors of the road network with the road expansion. The differences of road density in these regions were attributed to the differences of the number of nodes and corridors between the different regions. In addition, a, (3, y were positively correlated whereas were significantly negatively correlated with C, that is, the cost ratio decreased with the expansion of road network. Moran index further indicated that:before the construction, the road density inⅤwas decentralized, whereas they were relatively gathered inⅠ,Ⅱ,ⅢandⅣ. After the construction, the road density inⅠ,ⅢandⅤincreased significantly, while they increased slightly inⅡandⅣ. The reason for this is that the terrain ofⅡandⅥis relatively steep, while it is relatively flat inⅠ,ⅢandⅤ. So we found that:as a rural agricultural landscape corridor or channel for material flow and value flow, the rural roads can be evaluated by the network structure analysis, moreover by it can attain the rural road system network optimization.
(4) The landscape effect of rural road system
According the type, using the road as centerline, the degree of interference of rural roads on the surrounding land use pattern generally shows a gradual decay to both sides of the road. Across the paddy field, dry land and the regions which are the human settlements in, the field road make the most significant interference with the fragmentation of those regions. The results indicated:it made the most significant degree of interference with landscape connectivity within 25m, and the interference gradually weakened beyond 25m. Meantime, it brought severe interference with land use disturbance in 10-25m and the hugest one was within 10m. Exceeding 25m, the degree of interference gradually decayed away as the distance increased. In 0-25m interference band, degree of fragmentation of the land-use types from field road showed:dry land> paddy> settlement water> woodland, and in 25m-250m band showed:paddy field> dry> settlement> water> woodland. The intensity of interference pattern of land use from production path increased with distance adding within 2.5m, while it decreased with distance adding and the severest disturbance happened within 2.5-10m. It changed less in 10-30m and gradual decayed over 30m. In 0-20m interference band, degree of fragmentation of the land-use types from production road showed:paddy fields> dry> settlement> water> woodland, and in 25m-250m band showed:dry land> paddy> settlement> water> woodland.
According the landscape, using the road as centerline, the degree of interference of field roads on the surrounding landscape pattern also shows a gradual decay to both sides of the road, while interference of the production shows an increasing trend at first and then gradually decayed. The results indicated:the strongest intensity of disturbance on land use landscape from field road was in 5m, and it decreased with distance increasing beyond 5m. After the construction of field road, except IV which had a slightly increased of landscape fragmentation in the 0-10m, the landscape fragmentation in other four regions were improved or mitigated, they were almost same in the 10-250m. The complex bending degree of landscape border raised slight in a certain extent, and the degree of regular shape of the landscape types increased. The continuity of adjacent plots of preponderant land use in study areas increased overall, and the dominant landscape types was not threatened or even increased. The disturbance on landscape from production road increased with distance adding within 5 m, and the most severe of interference came from 2.5 to 5m band. In the 5-10m band, the disturbance was still large. Over 10m, however, the degree of interference gradually decayed away as the distance increased. The degree of the landscape fragmentation within the 0-30m was improved due to the construction of production road. Although it kept same within 30-120m, the complexity of landscape boundaries rose slightly while the degree of regular shape of the landscape types reduced slightly. Therefore, as a landscape type, the rural roads can optimize the reconstruction of local rural land use so that the efficient use can be achieved.
In summary, this paper demonstrated the idea about the hierarchy system of rural roads in Hilly-mountainous Region of Southwestern China by the layout and the structural design of production road and field road. It analyzed features of the network system of rural road in Hilly-mountainous Region of Southwestern China pre and post construction by indexes of corridor structure, network structure and the spatial autocorrelation (Moran). Basing on those, it discussed what influence on the surrounding land use pattern from the formation and development of rural roads. Thus it revealed the landscape effect pre and post construction of the rural road system in Hilly-mountainous Region of Southwestern. However, the landscape effect from road is not just in the impact on the surrounding land use, it also includes impact on regional transportation, human activity, community structure and organization and function and succession of ecosystems and so on. What is more, this effect works in the whole process of road building. Therefore, it is necessary to strengthen the research on human activity, community structure and organization, the dynamics of social and economic development which correlate with construction process of rural road system from multi-angle.
引文
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