Land use and land cover change analysis in predominantly man-made coastal wetlands: towards a methodological framework

In areas with a long history of human occupation, coastal wetlands have undergone extensive modification to accommodate extractive activities as salt-extraction and aquaculture. These man-made wetlands maintain some of the ecological functions of natural wetlands in spite of their artificial character: their suitability as complimentary waterbird habitat is well documented. In cases of wetlands composed of mixed natural and man-made areas, similarities in substrate-vegetation-water compositions may pose challenges in the applicability of remote sensing and GIS techniques for the study of landscape changes, requiring tailor-made, case-specific methods. We explored this supposition by testing these techniques for the study of the Bahia de Cadiz Nature Park (Spain). Using Landsat imagery spanning the 1985–2011 period, natural and man-made marsh areas were classified separately and results merged to produce land cover classification maps. Different change dynamics were observed for the natural and man-made areas, the latter exhibiting prominent changes, including widespread vegetative succession. Further, through the overlay of ancillary land use data for 2011, an integrated land use and cover map was produced for this year. Different scenarios arising from the abandonment of extractive activity and structural negligence were highlighted. Furthermore, a methodological framework for the classification of predominantly man-made wetlands was designed. The method is cost-effective and open for integration of additional datasets, and is considered a beneficial input to conservation and land use management. Its applicability for monitoring of landscape change not only pertains to the study area, but also extends to other coastal wetland areas of a similar nature.     

The importance of unmanaged coastal wetlands to waterbirds at coastal Ghana

Ghana's 550 km coastline has about 100 wetlands out of which five large ones are managed as Ramsar sites, the rest being unmanaged. Recent pollution and misuse of unmanaged wetlands have necessitated a study into their roles in the support of waterbirds. Waterbird survey on four wetlands between September 2005 and April 2006 revealed that 51 waterbird species make use of the managed compared to 44 in the unmanaged wetlands. Average numbers of waterbirds were higher on the managed wetlands (10,510 ± 4862) than on the unmanaged wetlands (1348 ± 602) (P < 0.05) but mean population density of waterbirds (n/ha) was the same for both the managed (1860 ± 310) and unmanaged (1400 ± 220) (P > 0.05) wetlands. The population densities of waterbirds belonging to guilds 1, 5 and 7 were significantly higher on the managed wetlands (P < 0.05). In contrast, guilds 2 and 4 have significantly higher population densities on the unmanaged wetlands while the population density of guild 3 was the same (P > 0.05). There was an indication that during mid and late periods of the nonbreeding season, the unmanaged wetlands altogether may support a larger number of waterbirds belonging to guilds 2, 3 and 4 than the five managed wetlands.     

Challenges in using land use and land cover data for global change studies

Land use and land cover data play a central role in climate change assessments. These data originate from different sources and inventory techniques. Each source of land use/cover data has its own domain of applicability and quality standards. Often data are selected without explicitly considering the suitability of the data for the specific application, the bias originating from data inventory and aggregation, and the effects of the uncertainty in the data on the results of the assessment. Uncertainties due to data selection and handling can be in the same order of magnitude as uncertainties related to the representation of the processes under investigation. While acknowledging the differences in data sources and the causes of inconsistencies, several methods have been developed to optimally extract information from the data and document the uncertainties. These methods include data integration, improved validation techniques and harmonization of classification systems. Based on the data needs of global change studies and the data availability, recommendations are formulated aimed at optimal use of current data and focused efforts for additional data collection. These include: improved documentation using classification systems for land use/cover data; careful selection of data given the specific application and the use of appropriate scaling and aggregation methods. In addition, the data availability may be improved by the combination of different data sources to optimize information content while collection of additional data must focus on validation of available data sets and improved coverage of regions and land cover types with a high level of uncertainty. Specific attention in data collection should be given to the representation of land management (systems) and mosaic landscapes.     

Assessing simulated land use/cover maps using similarity and fragmentation indices

Land use/cover changes (LUCC) are significant to a range of issues central to the study of global environmental change. Over the last decades, a variety of models of LUCC have been developed to predict the location and patterns of land use/cover dynamics. The simulation procedures of most computational LUCC models can be sub-divided into three basic steps: (1) a non-spatial procedure which calculates the quantity of each transition; (2) a spatial procedure that allocates changes to the more likely locations and eventually replicates the patterns of the landscape and; (3) an evaluation procedure to compare a simulated land use/cover map with the true map for the same date. Most of the evaluation techniques are focused on assessing the location of the simulated changes in comparison to the true locations and do not assess the ability of the model to simulate the overall landscape pattern (e.g. size, shape and distribution of patches). This study aims at evaluating simulated land use/cover map patterns obtained using two models (DINAMICA and Land Change Modeler). Simulated maps were evaluated using a fuzzy similarity index which takes into account the fuzziness of locations within a cell neighborhood with fragmentation indices. Results show that more realistic simulated landscapes are often obtained at the expense of the location coincidence. When aggregate patterns of a landscape are important (e.g. when considering fragmentation impacts on biodiversity), it is important to incorporate indices that take into account not merely location, but also the spatial patterns during the model assessment procedure.     

Assessing land cover change in Kenya's Mau Forest region using remotely sensed data

Kenya's Rift Valley has been undergoing rapid land cover change for the past two decades, which has resulted in ecological and hydrological changes. An effort is under way to quantify the timing and rate of these changes in and around the River Njoro watershed located near the towns of Njoro and Nakuru using remote sensing and geographic information system (GIS) methods. Three Landsat TM images, representing a 17‐year period from 1986 to 2003 in which the area underwent a significant land cover transition, were classified and compared with one another. Vegetation diversity and temporal variability, common to tropical and sub‐tropical areas, posed several challenges in disaggregating classified data into sub‐classes. An iterative approach for the resolving challenges is presented that incorporates unsupervised and supervised classification routines in coordination with knowledge‐based spatial analyses. Changes are analysed at three spatial scales ranging from the highly impacted and deforested uplands to the watershed and landscape scales. Land cover transitions primarily occurred after 1995, and included large forest losses coupled with increases in mixed small‐scale agriculture and managed pastures and degraded areas. These changes in cover type are highly spatially variable and are theorized to have significant impacts on ecological and hydrologic systems with implications for environmental sustainability.     

Evaluating changes in land cover and their importance for global change

During recent years, much progress has been made in integrating traditional natural science disciplines and in the developmnet of multidisciplinary models. This is crucial for an increased understanding of the dynamics of the Earth system. The domination of human activities in altering these dynamics is still increasing. However, few research projects have focused directly on understanding the motives for such intensification. It has only recently been acknowledged that improved understanding of human driving forces of global change is required to enable meaningful projections of plausible future states of the Earth system.     

盐城滨海湿地的土地利用/覆盖变化

盐城滨海湿地是中国最重要的海岸带湿地之一,对区域生物多样性维持及我国近海水质安全意义重大,近年来由于持续的开发利用导致生境质量发生了显著变化。为在景观水平上揭示盐城滨海湿地的动态趋势,选择1975、1991、2002和2006年Landsat遥感影像数据,对盐城滨海湿地土地利用/覆盖变化及其转移过程进行了研究。结果表明：1975—2006年,自然湿地面积减少了56%（1.5×10⁵hm²）,渔塘和农田的面积则分别增加了892%（8.2×10⁴ hm²）和165%（5.9×10⁴ hm²）;围垦及渔塘开挖等生产用地的扩张是滨海湿地土地利用/覆盖变化的主要形式,占土地利用变化总面积的75%,湿地的自然演替占11%,米草（Spartina spp.）的生物入侵占湿地整体变化面积的7%,但近年来有减缓趋势;盐城滨海湿地土地利用/覆盖变化主要存在“潮间带泥滩→碱蓬（Suaeda salsa）群落→渔塘（农田）”、“潮间带泥滩→碱蓬群落→芦苇（Phragmites communis）群落→渔塘（农田）”、“潮间带泥滩→米草→渔塘”等3类主要转移过程;自然湿地的大量减少将进一步压缩野生动物生存空间,对近海水体的净化能力也将下降,因此须加强对湿地围垦与开发利用的控制,加强对现有湿地资源的保护。     

Ornithological importance of coastal wetlands in Guinea

Fode, L.C. 2000. Omithological importance of coastal wetlands in Guinea. Ostrich 71 (1 & 2): 343.

For a number of years, the Guinean government has given high priority to nature conservation. Currently the conservation and wise use of natural resources are important issues of the country's developmental policy. The country has a rainy season of seven months (May-November), and heavy rainfall in the coastal area, an average of 2 000–4 000 mm/yr. Coastal wetlands cover a large area: 700 km² mud flats, 600 km² mangroves, 780 km² rice fields and several hundred km² freshwater swamp. Large numbers of waterbirds can be found in the Guinean coastal wetlands, and also in Senegal, Sierra Leone, Liberia, Cöte d'Ivoire, Guinea-Bissau, and Gambia. These countries share the same natural resources with Republic of Guinea, especially during the European winter, when, in addition to the Afrotropical species, there are many palearctic migrants. Over half a million waterbirds winter in the area, of which the palearctic waders, with 430 000, form the major part. Additionally, there are considerable numbers of flamingos, herons, egrets, and terns. The numbers of waterbirds during the European summer amount to 20% of those in winter, of the palearctic waders alone to 10%. In both seasons by far the largest number of waterbirds can be found on the mudflats. Various breeding waterbirds can be found on a few islands (> 3 000 pairs of brown booby, Sula leucogaster on the Isle of Alcatraz), and in the mangroves, rice fields and freshwater swamps. There are considerable breeding numbers of African Darter Anhinga rufa, Green-backed heron Buroroides striatus, White-necked stork Ciconia espiscopus and Caspian Tem Sterna caspia—breeding occurs mainly in the rainy season, except for the island, where most breeding takes place in the dry season. The Guinean coastal wetlands meet also the various criteria developed under the terms of the Ramsar Convention to identify wetlands of international importance. They easily meet the criterion of “regularly supporting 20 000 waterfowl” by the mere occurrence of large numbers during this period. The Guinean coastline, which has a length of 300 km, covers about a quarter of the West African mangrove coast between mid-Senegal and Sierra Leone. Although part of the mangroves have disappeared because of tree cutting and land reclamation for rice cultivation, these tidal forests still form a main part of the Guinean coast. Nearly all the well-developed large scale mangrove areas lie north of Conakry. According to some observations these are the three major threats to the coastal wetlands of Guinea: destruction of the mangrove habitats, hunting, disturbance of breeding sites, the latter being predominantly human disturbance of breeding bird colonies. Especially important is the destruction of parts of the mangrove zones by wood cutting and land reclamation in favour of rice cultivation. The Ninth Pan-African Ornithological Congress should be an opportunity to recommend the execution of appropriate national regional training programmes for concerned African countries. That programme will help to have solid specialists able to present adapted ornithological policies in the interested countries of Africa. The congress should also organise an official regional institution through which periodical contacts of specialists and quthorities can be made at local and international level. The congress must have some international development co-operation in ornithological fields in Africa. The congress may recommend development co-operation policy with Ramsar Convention Office, Wetlands International, WWF, IUCN, and any other concerned institutions.     

Partitioning global change: Assessing the relative importance of changes in climate and land cover for changes in avian distribution

Understanding the relative impact of climate change and land cover change on changes in avian distribution has implications for the future course of avian distributions and appropriate management strategies. Due to the dynamic nature of climate change, our goal was to investigate the processes that shape species distributions, rather than the current distributional patterns. To this end, we analyzed changes in the distribution of Eastern Wood Pewees (Contopus virens) and Red‐eyed Vireos (Vireo olivaceus) from 1997 to 2012 using Breeding Bird Survey data and dynamic correlated‐detection occupancy models. We estimated the local colonization and extinction rates of these species in relation to changes in climate (hours of extreme temperature) and changes in land cover (amount of nesting habitat). We fit six nested models to partition the deviance explained by spatial and temporal components of land cover and climate. We isolated the temporal components of environmental variables because this is the essence of global change. For both species, model fit was significantly improved when we modeled vital rates as a function of spatial variation in climate and land cover. Model fit improved only marginally when we added temporal variation in climate and land cover to the model. Temporal variation in climate explained more deviance than temporal variation in land cover, although both combined only explained 20% (Eastern Wood Pewee) and 6% (Red‐eyed Vireo) of temporal variation in vital rates. Our results showing a significant correlation between initial occupancy and environmental covariates are consistent with biological expectation and previous studies. The weak correlation between vital rates and temporal changes in covariates indicated that we have yet to identify the most relevant components of global change influencing the distributions of these species and, more importantly, that spatially significant covariates are not necessarily driving temporal shifts in avian distributions.     

北京城市土地利用/覆盖变化及其对雨洪调节服务的影响

深入认识城市土地利用/覆盖变化对雨洪调节服务的影响对于提升城市生态系统服务和雨洪管理具有重要意义。基于多期Landsat遥感影像,利用混合像元分解与人工目视解译集成的方法提取了北京市1991—2014年的土地利用/覆盖数据,模拟评估了不同降雨情景下的地表产流与雨洪调节服务,并分析了城市建成区的土地利用/覆盖变化对雨洪调节服务的影响。结果表明:1991—2014年,北京城市用地面积增长了1096.53 km²,建成区内不透水面比例上升了9.83%。城市建成区雨洪调节服务总体呈下降趋势,1a、10a、25a和100a一遇降雨情景下平均地表径流调节率分别下降了5.37%、2.40%、1.75%和1.04%,一定程度上加剧了城市的雨洪产流风险。同时,城市新扩张区的土地利用/覆盖变化对雨洪调节服务的影响较老城区更强,贡献度超过84%。建议未来城市新区发展应合理配置不透水地表和绿地空间以提升城市雨洪调节服务。     

A review of influences of land use and land cover change on ecosystems

随着人口的增长和人类社会的发展, 土地利用与土地覆盖变化已经是不可避免。土地利用与土地覆盖变化不仅对生态系统的要素、结构和功能产生深远的影响, 也会对全球变化产生反馈作用。针对土地利用与土地覆盖变化的过程、驱动机制以及在各个方面可能产生的生态环境效应的科学研究已经全面开展。该文综述了土地利用与土地覆盖变化对气候、土壤、生物地球化学循环、生物多样性以及区域生态环境等影响方面的研究进展, 并提出了相关研究的前沿方向展望。随着新技术的不断发展, 学者们将更多地侧重预测未来全球变化背景下的土地利用与土地覆盖变化趋势、合理性以及适应性, 为可持续发展提供基础资料和理论依据。     

土地利用与土地覆盖变化对生态系统的影响

随着人口的增长和人类社会的发展, 土地利用与土地覆盖变化已经是不可避免。土地利用与土地覆盖变化不仅对生态系统的要素、结构和功能产生深远的影响, 也会对全球变化产生反馈作用。针对土地利用与土地覆盖变化的过程、驱动机制以及在各个方面可能产生的生态环境效应的科学研究已经全面开展。该文综述了土地利用与土地覆盖变化对气候、土壤、生物地球化学循环、生物多样性以及区域生态环境等影响方面的研究进展, 并提出了相关研究的前沿方向展望。随着新技术的不断发展, 学者们将更多地侧重预测未来全球变化背景下的土地利用与土地覆盖变化趋势、合理性以及适应性, 为可持续发展提供基础资料和理论依据。     

辽宁沿海土地利用变化的图谱特征

土地利用变化图谱能够充分反映土地利用变化的时空过程,近年来引起了广泛的关注。本文分析了2000—2010年辽宁沿海地区土地利用变化的图谱特征。结果表明:2000—2005年土地利用变化图谱主要以耕地!建设用地和海域!湿地为主,分别占总变化面积的44.41%和18.16%;2005—2010年土地利用变化图谱主要以海域、湿地和耕地的转出为主,其中海域!湿地占总变化面积的23.43%,海域!裸地占22.69%,海域!建设用地占5.10%,湿地!建设用地占10.06%,耕地!建设用地占20.55%;2000—2010年土地利用变化模式图谱以后期变化型和前期变化型为主,分别占总变化面积的70.34%和29.17%,说明辽宁沿海地区土地利用变化具有明显的时间阶段性特征,前期变化体现了城镇化和海产养殖业的发展过程,后期变化体现了沿海开发和城镇化的进一步发展过程。     

Effectiveness of natural protected areas to prevent land use and land cover change in Mexico

This study evaluated the extent to which natural protected areas (NPAs) in Mexico have been effective for preventing land use/land cover change, considered as a major cause of other degradation processes. We developed an effectiveness index including NPA percentage of transformed areas (agriculture, induced vegetation, forestry plantations, and human settlements) in 2002, the rate and absolute extent of change in these areas (1993–2002), the comparison between rates of change observed inside the NPA and in an equivalent surrounding area, and between the NPA and the state(s) in which it is located. We chose 69 terrestrial federal NPAs, decreed before 1997, that were larger than 1,000 ha, not urban/reforested with non-native vegetation, not islands and not coastal strips, and estimated the extent of transformed areas using 1993 and 2002 land use/land cover maps. Over 54% of NPAs were effective, and were heterogeneously distributed by management categories: 65% of Biosphere Reserves, 53% of Flora and Fauna Protection Areas, and 45% of National Parks. 23% of NPAs were regarded as weakly effective, and the remaining 23% as non-effective. We recognize the importance of NPAs as a relevant conservation instrument, as half of NPAs analyzed (particularly biosphere reserves) prevented natural vegetation loss compared with their geographic context. Our results suggest that conservation based on NPAs in Mexico still faces significant challenges. Our approach can be expanded for evaluating the effectiveness of NPA in other regions, as land use/land cover maps are now available almost worldwide.     

三江平原土地利用/覆被变化对区域植被碳储量的影响

通过历史时期地图数字化和遥感图像解译得到三江平原1954～2005年的6期土地利用/覆被数据。根据IPCC《2006指南》提供的方法,评估土地利用/覆被变化对三江平原植被碳储量的影响。结果表明:三江平原1954～2005年土地利用/覆被变化显著,农田大面积增加,沼泽湿地、林地、草地面积锐减;土地利用/覆被变化主要发生在农田、沼泽湿地、林地和草地之间;农田是沼泽湿地、林地、草地的主要转出对象,林地的主要转入来源为农田和草地,沼泽湿地的主要转入来源为农田和林地。1954～2005年共有1.07×10³km²林地、5.73×10³km²草地和2.59×10⁴km²沼泽湿地转出为农田。土地利用/覆被变化导致三江平原植被碳储量不断减少,1954～2005年三江平原植被碳储量共减少57.48Tg。林地、沼泽湿地、草地向农田的转化及林地向草地、沼泽湿地的转化导致植被碳储量减少97.06Tg,农田向林地、沼泽湿地、草地的转化及草地、沼泽湿地向林地转化导致植被碳储量增加39.58Tg。     

敦煌市土地利用/覆盖变化特征及成因分析

利用ArcGIS9.2软件,结合野外调查,对敦煌市1987、1996和2007年3期Land-sat5-TM遥感影像进行解译,并分8个类型分析了土地利用/覆盖变化的特征及成因。结果表明:近20年来敦煌市呈现出植被覆盖程度不断降低、覆盖面积减小的趋势,其中耕作区、城建用地和无植被区面积净增,其他5类用地面积净减;8类用地类型之间互有转换,转移的主要方向是部分草地和无植被区转变为耕作区,水域湿地和灌木林地转变为草地,草地由高覆盖、中覆盖、低覆盖到无植被区逐次转变;除了耕作区边缘植被覆盖程度有所增加外,其他区域退化趋势明显;引起LUCC的自然因素中气温升高的影响较大,而人文因素中土地开垦、增加灌溉的影响较大。     

土地利用/覆盖变化对中国不同季节气温的影响

近几十年中国地区土地利用/覆盖变化(LUCC)较大,在区域气候模拟中尤其需要使用更加准确的土地利用/覆盖数据。基于模式原有的USGS和新开发的LUC90两种土地利用/覆盖资料,利用区域环境集成模拟系统(RIEMS2.0)分别进行连续10a模拟,分析LUCC对中国不同季节气温的影响。结果表明:1)采用LUC90资料后,中国及东北、华北、华南夏季平均气温增加,但只有东北模拟与观测值的偏差减小,且通过显著性检验(P0.01)。中国及东北、华南冬季平均气温增加,并且模拟与观测值的偏差减少。中国及华北和华南对冬季气温年际变率的模拟改善好于夏季。2)土地利用/覆盖变化通过影响潜热通量的变化和净吸收辐射通量的变化来影响不同季节气温的变化。冬季净辐射通量变化对气温变化的贡献较夏季大,而夏季潜热通量变化对气温变化的贡献较冬季大。雨养农田转变森林、草地、灌溉农田过程造成通量变化,其对气温变化的影响也存在不同分区季节的差异。     

Impact of land use and land cover change on groundwater recharge and quality in the southwestern US

Humans have exerted large‐scale changes on the terrestrial biosphere, primarily through agriculture; however, the impacts of such changes on the hydrologic cycle are poorly understood. The purpose of this study was to test the hypothesis that the conversion of natural rangeland ecosystems to agricultural ecosystems impacts the subsurface portion of the hydrologic cycle by changing groundwater recharge and flushing salts to underlying aquifers. The hypothesis was examined through point and areal studies investigating the effects of land use/land cover (LU/LC) changes on groundwater recharge and solute transport in the Amargosa Desert (AD) in Nevada and in the High Plains (HP) in Texas, US. Studies use the fact that matric (pore‐water‐pressure) potential and environmental‐tracer profiles in thick unsaturated zones archive past changes in recharging fluxes. Results show that recharge is related to LU/LC as follows: discharge through evapotranspiration (i.e., no recharge; upward fluxes <0.1 mm yr^?1) in natural rangeland ecosystems (low matric potentials; high chloride and nitrate concentrations); moderate‐to‐high recharge in irrigated agricultural ecosystems (high matric potentials; low‐to‐moderate chloride and nitrate concentrations) (AD recharge: ～130–640 mm yr^?1); and moderate recharge in nonirrigated (dryland) agricultural ecosystems (high matric potentials; low chloride and nitrate concentrations, and increasing groundwater levels) (HP recharge: ～9–32 mm yr^?1). Replacement of rangeland with agriculture changed flow directions from upward (discharge) to downward (recharge). Recent replacement of rangeland with irrigated ecosystems was documented through downward displacement of chloride and nitrate fronts. Thick unsaturated zones contain a reservoir of salts that are readily mobilized under increased recharge related to LU/LC changes, potentially degrading groundwater quality. Sustainable land use requires quantitative knowledge of the linkages between ecosystem change, recharge, and groundwater quality.     

Largely underestimated carbon emission from land use and land cover change in the conterminous United States

Carbon (C) emission and uptake due to land use and land cover change (LULCC) are the most uncertain term in the global carbon budget primarily due to limited LULCC data and inadequate model capability (e.g., underrepresented agricultural managements). We take the commonly used FAOSTAT‐based global Land Use Harmonization data (LUH2) and a new high‐resolution multisource harmonized national LULCC database (YLmap) to drive a land ecosystem model (DLEM) in the conterminous United States. We found that recent cropland abandonment and forest recovery may have been overestimated in the LUH2 data derived from national statistics, causing previously reported C emissions from land use have been underestimated due to the definition of cropland and aggregated LULCC signals at coarse resolution. This overestimation leads to a strong C sink (30.3 ± 2.5 Tg C/year) in model simulations driven by LUH2 in the United States during the 1980–2016 period, while we find a moderate C source (13.6 ± 3.5 Tg C/year) when using YLmap. This divergence implies that previous C budget analyses based on the global LUH2 dataset have underestimated C emission in the United States owing to the delineation of suitable cropland and aggregated land conversion signals at coarse resolution which YLmap overcomes. Thus, to obtain more accurate quantification of LULCC‐induced C emission and better serve global C budget accounting, it is urgently needed to develop fine‐scale country‐specific LULCC data to characterize the details of land conversion.