Quantification of landscape transformation due to the Fast Track Land Reform Programme (FTLRP) in Zimbabwe using remotely sensed data

After independence, Zimbabwe adopted two major land reform programmes to address the racially skewed land ownership. Due to the perceived failure of these programmes, the country embarked on a highly politicised and forceful acquisition and re-distribution of white owned commercial farms under the Fast Track Land Reform Programme (FTLRP). Whereas a large number of Zimbabweans have been allocated land under the programme, there has been a significant decline in agricultural productivity and an increase in degradation of land and associated resources. Popular opinion has even suggested the country’s current socio-economic challenges are linked to the programme. Mitigating land degradation, enhancing agricultural productivity and promoting natural resources sustainability requires an objective understanding and determination landscape transformation within relevant administrative decision making spatial extents. In this study, we adopted multi-temporal remotely sensed imagery to determine landscape transformation after the implementation of the FTLRP in Chipinge administrative district, characterised by heterogeneous land usage and natural resources. Major land-use-land-cover types were determined using the Support Vector Machine classification algorithm and accuracy established using field survey and ancillary data. Results show significant landscape transformation after the implementation of the FTLRP. Specifically, there was a decline in plantations, small farms, water bodies and forests and an increase in bare areas and settlements. This study demonstrates the value of remotely data in monitoring landscape transformation arising from a shift in policy. Furthermore, these results provide an insight into multi-temporal spatial changes in cultivated, natural and degraded lands, valuable for designing measures to improve landscape productivity and to adopt relevant rehabilitation measures. Understanding multi-temporal landscape change within an administrative boundary is particularly valuable for area specific planning, policy formulation and adoption of desired mitigation measures.     

Understanding recurrent land use processes and long-term transitions in the dynamic south-central United States,c. 1800 to 2006

Forests have historically been under significant land use pressures that cause periods of degradation, clearance, and recovery. To understand these changes, studies are needed that place trends in a historical landscape context and also examine recent dynamics. Here, we use historical investigation (c. 1800) and an examination of land use and land cover change between 1973 and 2006 to establish a baseline trajectory of the forested system of the south-central United States (US) plains. The study culminates in a highly detailed accounting of the processes and causes of land change between 2001 and 2006. In the study region, the forest transitioned from early low-intensity use, to clearance for farming and timber, to widespread recovery from degradation beginning in the 1930s. By 1970, the region was transitioning from recovered woodlands to an intensive regime of recurrent timber harvest and replanting. The recurring cycle inherent in intensive silviculture has been the main cause of land change for the past several decades, accounting for more than 95% of the total extent of change between 2001 and 2006. The transition to forest recovery in the south-central US was an important historical occurrence. However, the dynamic post-transition landscape needs to be better understood.     

Changes in land use, land tenure, and landscape fragmentation in the Tijuana River Watershed following reform of the ejido sector

Changes in land use and land tenure can influence both physical fragmentation and ownership fragmentation of landscapes, with implications for biodiversity. In this study, we evaluated changes in land use and land tenure in the Tijuana River Watershed, a region of high biodiversity and endemism, following the implementation of a new Agrarian Law which allowed for privatization and sales of communal land (ejidos) beginning in 1992. In order to understand changes in land use and cover, we constructed maps from aerial photographs and Aster images and measured changes between 1994 and 2005. In order to understand changes in land tenure, we collected data from Mexican government sources on ejido land size, ownership, and sales, and we conducted 55 structured interviews with ejidatarios in the watershed. Our results demonstrate that land-use/cover change between 1994 and 2005 was dominated by an increase in urban area and grasslands, and a decrease in coastal sage scrub, chaparral, and, to a lesser degree, agriculture. In particular, the conversion of coastal sage scrub has left a far more fragmented landscape than existed in 1994. In addition, most of the ejidos in the watershed, as well as individuals interviewed, had participated in some stage of the land certification and titling process allowed by the new Agrarian Law, resulting in substantial changes in land tenure. However, land tenure security appeared to play a larger role than a desire to sell land and, contrary to studies from other regions, full title to the land was obtained in a range of urban and rural settings, rather than primarily on land closest to urban zones. Our results suggest that past predictions regarding future urban growth and fragmentation of native vegetation in the region have proven accurate and highlights regions of change that merit further study.     

论土地利用/土地覆盖变化驱动力研究

驱动力研究是土地利用/土地覆盖变化(LUCC)研究的重要组成部分,意义重大。在论述土地利用/土地覆盖变化驱动力研究内容的基础上,对国内外的驱动力研究现状及研究方法进行了初步总结,并提出了目前土地利用/土地覆盖变化驱动力研究中应该注意的几个关键问题。     

覆土深度对腐蚀混凝土排水管道CIPP修复前后力学性能的影响分析

原位固化法(CIPP)修复技术因其不需注浆、施工速度快、过流面积损失小等优点,成为目前应用最为广泛的管道非开挖修复工艺之一。上覆土压力是管道上方最重要的恒载。为深入探讨覆土深度对排水管道CIPP修复前后力学性能的影响,基于ABAQUS有限元数值模拟软件建立三维数值模型,对不同覆土深度下管道CIPP修复前后承插口、管顶及管底力学性能进行研究。结果表明：管道最大主应力随着覆土深度的增加而增加,管道竖向位移随着覆土深度的增加而减小;CIPP修复对于管道结构性能的提升具有显著效果,CIPP修复之后,管道受力变小且更加合理,竖向位移变小,服役性能增强。     

From the Holocene to the Anthropocene: A historical framework for land cover change in southwestern South America in the past 15,000 years

The main forest transitions that took place in south-central Chile from the end of the last glaciation to the present are reviewed here with the aim of identifying the main climatic and socio-economic drivers of land cover change. The first great transition, driven primarily by global warming, is the postglacial expansion of forests, with human populations from about 15,000 cal. yr. BP, restricted to coastlines and river basins and localized impact of forest fire. Charcoal evidence of fire increased in south-central Chile and in global records from about 12,000 to 6000 cal. yr. BP, which could be attributed at least partly to people. The subsequent expansion of agriculture led to much clearing of forests and the spread of weeds and other indicators of open habitats. The Spanish colonial period in America may have been followed by a transient expansion of forest cover into abandoned land, as indigenous population declined rapidly due to disease and slaughter. The 18th and 19th centuries brought about extensive loss of forests due to the massive impact of lumber extraction for mining operations both in central Chile and in western North America. Two centuries of intensive deforestation, coupled to grazing by cattle and extremely variable rainfall had long-lasting effects on forest cover in south-central Chile, which persist until today. The transition from a preindustrial to an industrial society brought about the “golden age” of timber harvest, assisted by mobile sawmills and railway transportation since the late 1800s. These advances led to the exhaustion of native commercial timber by the late 20th century in south-central Chile. In North America, harvestable stands were exhausted in New England and the Midwest around 1920. Settlement of the independent territories in the late 1800s and early 1900s implied vast burning and clearing of land and mounting soil erosion. Industrial forestry, based on government-subsidized massive plantations of short-rotation exotic trees, developed in the late 20th century, in connection with postindustrial displacement of exploitative activities from developed to third-world nations. In the last two decades, economic globalization and free trade promoted the expansion of new crops and further decline of woodlands, despite modest increases in forest cover. These patterns are repeated in many Latin American countries. To prevent further depletion of native forest resources and to provide an insurance against climate change, in the 21st century developing nations should aim at: (1) relocating subsidies from fiber farms to restoring diverse forest cover, (2) promoting ecosystem management of diverse forest and crops within landscapes, and (3) fostering diverse cultural relationships between people and their land.     

基于马尔柯夫模型的酒泉市肃州区LUCC趋势预测

甘肃省酒泉市近年来经济发展迅速,但生态环境也遭到一定程度的破坏;拟通过对其土地利用和覆盖变化的研究,为环境保护与经济协调发展提供决策支持;依据肃州区1988～2000年土地利用变更调查数据,对该区域LUCC进行分析,确定了土地利用类型的转移概率矩阵,并用马尔柯夫链模型预测了该区LUCC趋势。结果表明,肃州区土地利用将呈现耕地、水域和建设用地增加,林地、草地和未利用土地减少的发展趋势。     

基于残差U-Net的遥感影像土地覆盖类型自动分割

研究目的:土地覆盖的准确分割对于土地调查和规划具有重要意义。针对传统方法对于高分辨率遥感影像分割存在精度和效率较低等问题,提出了深度学习遥感影像分割方法。研究方法:以2 m高分辨率遥感影像为数据源,选用一种加入残差块的U-Net模型(ResU_Net),对目标区域进行基于深度学习的土地覆盖分割,并与SVM、PSPNet、U-Net分割方法进行对比。研究结果:ResU_Net能够更加准确地表达高分辨率遥感影像的地物信息,该方法总体分割精度达到85.50%,Kappa系数为0.7603,总体精度和Kappa系数均高于SVM、PSPNet和U-Net分割方法(总体精度:ResU_Net(85.50%)>U-Net(79.44%)>PSPNet(78.90%)>SVM(66.80%))。研究结论:ResU_Net模型对高分辨率遥感影像的土地覆盖分割效果更优。     

基于生态功能分区的湖北省土地利用及其生态服务价值变化研究

以1996年和2009年两期数据为基础,结合湖北省生态功能分区,对不同的生态功能区的土地利用及其生态服务价值的变化进行了对比分析,结果表明:1研究期间,对土地生态服务价值变化产生核心影响的是林地、草地以及耕地之间的剧烈变化;湖北省整体土地生态服务价值有所增加,但局部存在结构性问题;2鄂西三大区及幕阜山地区作为湖北省生态屏障,退耕还林的实施使其生态服务功能大幅增强,武汉地区在满足建设用地需求的同时大力恢复水域和林地,取得了生态环境和经济协调发展的效果,而保耕地的任务则基本转嫁于鄂中地区以及桐柏-大别山地区,其生态服务价值均有所减少或增长微弱;3湖北省东西四大山地必须加大对林地的保护力度;武汉地区需控制对耕地的侵占,减轻其他地区耕地保护的压力;鄂中地区则必须注意水域的保护及恢复,加强林地尤其是沿江防护林的建设。同时可通过实行区域间的生态补偿政策,以弥补地理空间上生态环境和经济利益的不平衡。     

基于比值植被指数的建设用地覆盖变化研究

基于中巴资源卫星遥感影像数据,利用比值植被指数对徐州市2001年,2005年,2008年3年的建设用地覆盖情况进行提取,探究比值植被指数应用于建设用地提取的可行性。通过比较2001—2008年间建设用地变化情况,发现徐州建设用地覆盖呈增长趋势,2005—2008年较2001—2005年增速稍缓。结果表明,利用比值植被指数对遥感影像分析,可以快速地获取建设用地覆盖变化情况,为未来几年发展的预测与规划提供参考。