Improvement of farmland fragmentation measurement model based on road network analysis
GEYujuan, ZHAOYuluan College of Geography and Environmental Science, Guizhou Normal University, Guiyang 550001, China 通讯作者:通讯作者:赵宇鸾,E-mail:zhaoyl.09b@igsnrr.ac.cn 收稿日期:2018-08-29 修回日期:2018-12-9 网络出版日期:2019-04-25 版权声明:2019《资源科学》编辑部《资源科学》编辑部 基金资助:国家自然科学基金项目(41771115)贵州省科技计划项目(黔科合平台人才[2017]5726号)2015年贵州省“千”层次创新型人才资助项目(111-0317003) 作者简介: -->作者简介:葛玉娟,女,内蒙古赤峰人,硕士研究生,主要研究方向为土地资源利用与管理。E-mail:986956266@qq.com
关键词:土地评价;耕地细碎化;GIS网络分析技术;道路通达性;农户;贵州省小坝村 Abstract This study used GIS network analysis technique to improve the accuracy of an arable farmland fragmentation measurement model. It first summarized the connotation of arable farmland fragmentation and the existing measurement methods. It proposed that the actual road network is an indispensable indicator for the determination of the degree of arable farmland fragmentation. Second, according to the connotation of arable farmland fragmentation, three indicators farmer’s plot road accessibility index, farmer’s plot area index, and farmer’s plot shape index based on road network were selected, and a new arable farmland fragmentation measurement model was constructed. Finally, an empirical analysis of 206 farming households in a typical study area was carried out with the improved arable farmland fragmentation measurement model to confirm the validity of the model, and to compare the Euclidean distance between the farmhouse and the cultivated land and the road network distance. Then we compared and analyzed the difference between the farmer’s Euclidean distance to the cultivated land and the road network distance using the two distance measurement methods. Compared with the road network distance, the Euclidean distance underestimated the level of cultivated farmland fragmentation. The improved measurement model of this study has positive significance for further research on cultivated farmland fragmentation and its impact on agricultural production input-output.
小坝村隶属于贵州省贵阳市修文县洒坪镇(图1),村境东西长3.536 km,南北宽3.214 km。是典型的喀斯特丘陵地貌,石漠化现象显著;土壤以黄壤为主,伴随零星石灰土分布;气候属亚热带湿润季风气候,气候温和,雨热同期,降水丰沛。研究调查农户206户,共计861人,劳动力为499人,占总人口的58%。小坝村经济以农业为主,土地面积为470 hm2,其中林地面积126.924 hm2,耕地面积103.730 hm2,耕地地块总数为934块,地块平均面积为0.110 hm2。小坝村宅基地多集中分布在通村公路两侧,呈条带状分布,少数住户居住较分散。受地形地貌的影响显著,耕地多集中在坝地或坝周山地缓坡地带。该村人多地少,耕地细碎化现象突出,为山区耕地细碎化研究提供了典型案例。 显示原图|下载原图ZIP|生成PPT 图1研究区概况图 -->Figure 1The study area -->
4.2 数据来源与处理
高分辨率遥感影像数据系采用无人机于2017年7月17日获取村庄航拍影像图(像元空间分辨率达到0.1 m),并运用ArcGIS10.1与ENVI5.3对获取的无人机航拍影像图进行校正、拼接等预处理,然后通过监督分类与人机交互式解译提取宅基地、耕地、道路(村间路、机耕路)等要素。共计获取206户宅基地、934块耕地地块、4059条道路,初步构建了小坝村地表信息数据库。最后运用2017年10月29日Google Earth获取的遥感影像与实地考察两种方式对分类结果进行室内验证与野外勘查,经验证,影像解译精度达到97.26%,解译效果较好。 在内业生产道路网络矢量数据过程中,运用ArcGIS空间分析工具(Spatial Analyst Tool)和网络分析工具(Network Analysis Tool)搭建路网(图2),测量出农户宅基地到其耕作地块的道路网络距离。需要说明的是,由于ArcGIS的网络分析工具是针对点对点的分析,而农户宅基地和其耕作地块是面状的矢量图斑,因此,通过空间分析工具生成宅基地与其耕作地块的中心点来代表其位置。同时为保证可以准确、有效地计算道路网络距离,需要对路网数据进行拓扑处理,去除重复线、合并假节点等[35],经处理后,每条线只要相交,便产生线段和节点,线段末端都具有一个端点。 显示原图|下载原图ZIP|生成PPT 图2小坝村路网分布情况 -->Figure 2Distribution of the road network in Xiaoba Village, Guizhou Province -->
为获取2017年研究区农户家庭基本情况、地块与宅基地权属、耕地利用现状、生产资料投入、劳动力投入、作物产出等信息,研究小组于2018年1月赴小坝村开展入户调研,采用参与式调查方法,在对村长、小组长访谈基础上,对农户进行逐户调查访问,获取有效问卷206份,得到小坝村及各农户的宅基地、耕地利用基本信息,并将宅基地户主等信息录入到小坝村地表信息数据库中,构建了涵盖耕地、宅基地空间信息和权属信息的小坝村耕地细碎化研究数据库(表1)。 Table 1 表1 表1农户调查数据描述性统计结果 Table 1Descriptive statistics of farming household survey data
为定量分析各指标现状值与农户耕地细碎化指数之间的关系,选取小坝村农户耕地细碎化指数为因变量( ),农户地块通达性( )、农户地块面积指数( )及农户地块形状指数( )为自变量,逐个进行回归分析(图4)。各指标( )与农户耕地细碎化指数( )均呈线性正相关关系,回归系数分别为1.233、2.887、1.812,判定系数R2分别为0.942、0.570、0.068;相关系数r分别为0.971、0.755、0.262,双侧显著性检验概率P值均为0。其中农户地块道路通达性指数与耕地细碎化指数拟合程度最优,相关性最高;农户地块形状指数与耕地细碎化指数相关性较低。拟合回归方程如下: (8) (9) (10) 显示原图|下载原图ZIP|生成PPT 图4评价指标与农户耕地细碎化指数的相关关系 -->Figure 4Correlation of evaluation indicators and land fragmentation index (LFI) -->
4.3.3 村庄耕地细碎化 依据公式(2)计算,小坝村耕地细碎化指数为88.570。计算各指标值占村庄耕地细碎化指数的比重,得到各指标对村庄耕地细碎化指数的贡献率(图5),图5表明贡献率最大的是农户地块道路通达性指数,占49.2%,其次为农户地块面积指数,最后是农户地块形状指数。由此可以看出,农户地块道路通达性是村庄耕地细碎化的重要影响因素。 显示原图|下载原图ZIP|生成PPT 图5各评价指标对村庄耕地细碎化指数的贡献率 -->Figure 5Contribution ratio of each evaluation indicator to village cultivated land fragmentation index (CLFI) -->
4.3.4 耕作道路网络距离与直线距离对比分析 如图6所示,为验证距离对耕地细碎化测定结果的影响,构建了以农户宅基地到其耕作地块的耕作道路网络距离为评价指标的模型A(即LFI和CLFI),以及使用农户宅基地到其耕作地块的直线距离的模型B进行比较。模型A、B计算所得的农户耕地细碎化指数呈现非常相似的趋势,但模型A评价结果分布更加分散。两个模型计算的结果具体区别在于:模型A(LFI)给出了较高的值,最小值为10.920,最大值为214.040,平均值(CLFI)为88.570;模型B的最小值为10.610,最大值为144.760,平均值为68.740,尽管两个模型所得的最小值很接近,但值得注意的是最大值存在很大的差距,模型A的平均值(CLFI)也比模型B高19.830。基于上述分析,可以认为用直线距离表示耕地地块的分散性低估了耕地细碎化程度,因此在测度耕地细碎化水平时,采用道路网络距离来表示农户宅基地到其耕作地块的耕作距离是很有必要的。 显示原图|下载原图ZIP|生成PPT 图6模型A与模型B农户耕地细碎化指数比较 -->Figure 6Comparison of land fragmentation index (LFI) values between Model A and Model B -->
本文重点研究的是运用道路网络分析技术构建耕地细碎化测度模型,并针对模型中的距离问题进行深入探讨。但模型仅在山区开展了应用与验证,缺乏在其他地形条件下的对比研究。此外,模型对遥感数据质量要求较高,一般多为无人机影像或高分辨率卫星影像,大尺度省、区域级别高分辨率影像的获取还需进一步讨论。在模型中提到的时间换算系数是通过实际调研得到的,因此,模型中时间换算系数在其他地区应用时需要根据区域实际进行调整。在以后的相关研究中,应主要集中于:详细分析不同耕地细碎化水平下农户土地利用决策行为的差异,分别探讨农户地块道路通达性指数、农户地块面积指数、农户地块形状指数与劳动力和资本投入、土地产出的关系,从而揭示耕地细碎化对耕地利用集约度、农业生产效率的影响过程和机制。 The authors have declared that no competing interests exist.
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