Seasonal changes in the relationship between species richness and community biomass in grassland under grazing and exclosure, Horqin Sandy Land, northern China

How species diversity–productivity relationships respond to temporal dynamics and land use is still not clear in semi-arid grassland ecosystems. We analyzed seasonal changes of the relationships between vegetation cover, plant density, species richness, and aboveground biomass in grasslands under grazing and exclosure in the Horqin Sandy Land of northern China. Our results showed that in grazed and fenced grassland, vegetation cover, richness, and biomass were lower in April than in August, whereas plant density showed a reverse trend. Vegetation cover during the growing season and biomass in June and August were higher in fenced grassland than in grazed grassland, whereas plant density in April and June was lower in fenced grassland than in grazed grassland. A negative relationship between species richness and biomass was found in August in fenced grassland, and in grazed grassland the relationship between plant density and biomass changed from positive in April to negative in August. The relationship between the density of the dominant plant species and the total biomass also varied with seasonal changes and land use (grazing and exclosure). These results suggest that long-term grazing, seasonal changes, and their interaction significantly influence vegetation cover, plant density, and biomass in grasslands. Plant species competition in fenced grassland results in seasonal changes of the relationship between species richness and biomass. Long-term grazing also affects seasonal changes of the density and biomass of dominant plant species, which further affects the seasonal relationship between plant density and biomass in grasslands. Our study demonstrates the importance of temporal dynamics and land use in understanding the relationship between species richness and ecosystem function.     

Land Changes Fostering Atlantic Forest Transition in Brazil: Evidence from the Paraíba Valley

The Atlantic Forest biome has only 13 percent of its pristine vegetation cover left. This article analyzes the consequences of land changes on forest cover in the Paraíba Valley, São Paulo state, Brazil, from 1985 to 2011. Multitemporal satellite image classifications were carried out to map eight land use and land cover classes. The forest cover increased from 2,696 km² in 1985 to 4,704 km² in 2011, mostly over areas of degraded pastures. The highest rates of afforestation were observed within protected areas around eucalyptus plantations. On the other hand, deforestation processes were concentrated on areas covered by secondary forests. Socioeconomic changes taking place in particular Brazilian settings, such as industrialization and agricultural modernization, allied to the Paraíba Valley's natural biophysical constraints for agricultural production, have led the region to experience a remarkable case of forest transition.     

The effects of enclosures and land-use contracts on rangeland degradation on the Qinghai–Tibetan plateau

Rangeland degradation on the Qinghai–Tibetan Plateau is a growing concern, often attributed to climate change and overgrazing. A minority of researchers have suggested instead that degradation may be caused by changes in land management, particularly enclosures and the contracting of long-term rangeland use rights to households. However, these claims have been hampered by a lack of empirical evidence. This field experiment is the first to compare rangeland conditions over time in the case of different management regimes on the Qinghai–Tibetan Plateau, specifically single-household versus multi-household management. A survey of vegetation properties in Maqu County, Gansu province in 2009, and repeated in 2011, examined the differences between single- and multi-household management in terms of vegetation biomass, cover, and species richness. In 2009, the biomass of the sedge group under multi-household management was significantly higher than that under single-household management. In 2011, biomass, vegetation cover, and species richness were all significantly higher under multi-household management than single-household management. These data suggest the flaws of the tragedy of the commons assumptions underlying single-household management.     

Global and local policy forces for landscape perennialization in central North American agriculture

Farm production practices often focus on mitigating negative consequences of cropping – particularly annual crops like corn, cereals and oilseeds. Some of North America’s most-intensive farmlands are rapidly converting their remaining perennial cover to annual crops. While perennial cover like woodlands, grasslands and wetlands are valued for the many landscape services they provide, they are vulnerable to conversion to other cover types under drivers of landscape change. Conversions within farms constitute nuances rather than new land uses, yet landscape composition effects can be substantial when considering habitat, biodiversity, soil and water quality, carbon sequestration, and aesthetics. As the farm landscape becomes increasingly dominated by annual crop vegetation, the key drivers behind land cover types and management merit critical examination. This paper reviews recent studies on farmland composition and management in central Canada and the United States, identifying trajectories and magnitudes of landscape changes. To consider forces, both speculative examination of policies and information from farmer interviews help identify motivations for changes in perennial or annual proportions of farm landscapes. The paper concludes with forces that increase perennialization and existing or prospective pathways to improve the balance between annual and perennial vegetation.     

Changes in intensity of wind erosion at different stages of degradation development in grasslands of Inner Mongolia, China

Overgrazing by increasing numbers of livestock in the Horqin Sandy Land of Inner Mongolia, China, has led to extensive degradation of the region's sandy steppes. Degraded grasslands are generally classified into four main types: fixed (least degradation), semi-fixed (light degradation), semi-shifting (moderate degradation) and shifting (severe degradation) sandy lands, representing four stages of degradation development. An experiment was conducted in the Horqin Sandy Land to investigate changes in intensity of wind erosion at different stages of degradation development in sandy grasslands and determine the extent to which surface wind erosion was affected by surface-related soil and vegetation factors through their effects on surface roughness length and wind regimes. Daily wind erosion rate was monitored at four sites of degraded grassland over an erosive period from 1 April to 10 June in 2001. Soil and vegetation properties for these sites were also measured twice: one in mid-April prior to the establishment of vegetation and again in mid-June after the establishment of vegetation. Relationships between surface roughness length and soil and vegetation variables were examined at each of the two stages of vegetation development. This study shows striking differences in the intensity of surface wind erosion among sites. The daily wind erosion rate in the fixed sandy land was, on average, only about 1/5 of the rate in the semi-fixed sandy land, 1/14 of the rate in the semi-shifting sandy land and 1/47 of the rate in the shifting sandy land suggesting a much higher resistance of the fixed sandy land to wind erosion compared to other sites. Differences in rate of wind erosion between sites were attributed to between-site differences in soil and vegetation properties that exerted significant effects on wind regimes by altering surface roughness length. At the pre-establishment stage of vegetation, surface roughness length was determined by a combination of litter amount on the ground, soil surface hardness and soil moisture content, with litter amount explaining the greatest proportion of the variation. At the post-establishment stage of vegetation, the development of the surface roughness effects was mainly governed by vegetation characteristics (vegetation cover in particular), while the effects of soil surface hardness and soil moisture on surface roughness length are likely to be masked by vegetation effects. The findings suggest that better management practices of restoring vegetation in degraded grasslands are required to reduce soil erosion losses and achieve a sustainable livestock production in the Horqin Sandy Land, an ecologically fragile sandy land ecosystem.     

Effects of dune stabilization on vegetation characteristics and soil properties at multiple scales in Horqin Sandy Land, Northern China

Ecological patterns and processes in dune ecosystems have been a research focus in recent years, however information on how dune stabilization influences vegetation and soil at different spatial scales...     

Preference for Grassland Heterogeneity: Implications for Biodiversity in the Great Plains

The Great Plains of the United States is a grassland region managed primarily for homogeneity associated with production agriculture. The resulting decline of obligate fauna makes enhancing biodiversity an increasingly important ecological goal. A survey was administered to land managers and the general population in ranching regions of Nebraska, Kansas, Oklahoma, and the Texas Panhandle. This research explores the preferred characteristics of privately owned grasslands among ranchers and the general population for vegetation structure and biodiversity. Results indicate a knowledge gap between biodiversity and the vegetation heterogeneity required to support it. Preference for grassland structure is seen as a sociocultural driver of decisions on management practices that constrain adoption of heterogeneity management. Conserving biodiversity and enhancing ecosystem services provided by heterogeneous grasslands can be accomplished by demonstrating that conservation advantages of heterogeneity and production agriculture are compatible.     

Land use and land cover change in Greater Dhaka, Bangladesh: Using remote sensing to promote sustainable urbanization

This study evaluates land use/cover changes and urban expansion in Greater Dhaka, Bangladesh, between 1975 and 2003 using satellite images and socio-economic data. Spatial and temporal dynamics of land use/cover changes were quantified using three Landsat images, a supervised classification algorithm and the post-classification change detection technique in GIS. Accuracy of the Landsat-derived land use/cover maps ranged from 85 to 90%. The analysis revealed that substantial growth of built-up areas in Greater Dhaka over the study period resulted significant decrease in the area of water bodies, cultivated land, vegetation and wetlands. Urban land expansion has been largely driven by elevation, population growth and economic development. Rapid urban expansion through infilling of low-lying areas and clearing of vegetation resulted in a wide range of environmental impacts, including habitat quality. As reliable and current data are lacking for Bangladesh, the land use maps produced in this study will contribute to both the development of sustainable urban land use planning decisions and also for forecasting possible future changes in growth patterns.     

SPATIO-TEMPORAL ASPECTS OF LAND USE AND LAND COVER CHANGES IN THE NIAH CATCHMENT, SARAWAK, MALAYSIA

This paper focuses on the large‐scale land use and land cover changes that have taken place in Sarawak state, East Malaysia over the three decades of 1972‐2002. Results are presented from a detailed land use and cover change (LUCC) study in the Niah River catchment using satellite imagery, questionnaire surveys and interviews. Successive waves of land cover changes have taken place. Large forest areas have been logged and gradually replaced by oil palm plantations, which now occupy more than 40 per cent of the total land area in the catchment. Concurrently, small‐scale farming systems have also changed. Formerly dominant Iban shifting cultivation practices are increasingly being replaced by cash crop production on permanent fields and impacted by off‐farm activities involving many ethnic groups. It is argued that land cover changes are continuous and complex processes involving a large number of variables which can be analysed for different time periods at various scales.     

Albedo-NDVI特征空间及沙漠化遥感监测指数研究

利用遥感数据和野外调查数据分析了沙漠化与地表定量参数之间的关系,提出了Albedo-NDVI特征空间的概念以及基于Albedo-NDVI特征空间的沙漠化遥感监测模型,即沙漠化遥感监测差值指数模型(DDI)。这个模型充分利用了多维遥感信息,指标反映了沙漠化土地地表覆盖、水热组合及其变化,具有明确的生物物理意义。而且指标简单、易于获取,有利于沙漠化的定量分析与监测。     

东洞庭湿地植被格局变化及其影响因素

东洞庭湖(也称东洞庭)湿地植被格局的变化特征及其影响因素的分析是该地区湿地植被保护与恢复策略制定的基础。基于美国陆地资源卫星Landsat TM/ETM+数据,应用决策树分类法分别提取东洞庭湖1999年、2002年、2006年三个时期湿地景观信息,通过转移矩阵法和质心迁移法对植被的时空演变分析。结果表明:(1)1993～2002年东洞庭湖芦苇、林地、苔草滩地面积均有所增加,芦苇增长速度最快,年均增长面积为28.93km²;2002～2006年林地面积迅速增加,年均增长面积为29.655km²,苔草面积有所减少,芦苇面积保持基本稳定;(2)东洞庭湖湿地植被质心呈现从林地—芦苇—苔草逐层靠近湖心的分布特点,1993～2006年三种植被类型的质心均不断向湖心迁移,其中以林地与芦苇的变迁更为显著。     

Rabbits,weeds and crops: Can agricultural intensification promote wildlife conflicts in semiarid agro-ecosystems?

Agricultural intensification has led to the extreme simplification of agricultural landscapes. The subsequent impoverishment of farmland plant communities can drive dramatic changes in the associated food webs of agricultural systems, with potential implications for vertebrate pest management. Weeds may provide alternative food sources for damaging species and thus contribute to reducing their damage, which is particularly desirable if the species is a valuable resource in its own right. Wild rabbits (Oryctolagus cuniculus) are a game species of great conservation value in the Iberian Peninsula that cause frequent damage to crops. Here we describe the dynamics of non-crop plant communities over an annual cycle in a semiarid Mediterranean agro-ecosystem, and discuss the potential linkages and implications for rabbit damage management. Overall, the availability of alternative food for rabbits was very low, especially in the most extensive habitat types, i.e. olive groves and vineyards. The seasonal pattern in plant productivity, which coincides with the phenology of rabbits in Mediterranean areas was only detectable in the less intensively managed habitat types. Scarce natural vegetation remnants retained the highest richness, diversity and plant cover, potentially acting as a refuge for both, plants and rabbits. Our results indicate that intensive management practices, through reducing alternative food sources for rabbits, are likely to promote conflict between hunters, farmers and conservationists in semiarid agro-ecosystems of Southern Spain.     

准格尔丘陵沟壑区五分地沟流域土地覆盖分析(英文)

以准格尔丘陵沟壑区五分地沟流域为研究区,应用彩红外航片和IKONOS卫星影像,绘制了1987、2002年土地覆盖/植被类型图,并数字化基于地面土地利用调查绘制的1979年土地利用图.利用景观格局指数,评价了研究区土地覆盖/植被空间格局现状及土地覆盖类型动态变化;并以ETM 数据为信息源,绘制了2002年土地覆盖/植被类型图.研究表明:2002年研究区土地覆盖/植被呈现出一个耕地、草地、人工乔木林和人工灌木林以及种植稀疏灌木的草地高度镶嵌的景观格局特征;20年内土地覆盖类型发生了显著的变化,景观异质性增强.基于研究区景观的高度破碎化,绘制小流域精细尺度土地覆盖图,高空间分辨率遥感数据十分必要.     

准格尔丘陵沟壑区五分地沟流域土地覆盖分析

以准格尔丘陵沟壑区五分地沟流域为研究区,应用彩红外航片和IKONOS卫星影像,绘制了1987、2002年土地覆盖/植被类型图,并数字化基于地面土地利用调查绘制的1979年土地利用图.利用景观格局指数,评价了研究区土地覆盖/植被空间格局现状及土地覆盖类型动态变化;并以ETM 数据为信息源,绘制了2002年土地覆盖/植被类型图.研究表明:2002年研究区土地覆盖/植被呈现出一个耕地、草地、人工乔木林和人工灌木林以及种植稀疏灌木的草地高度镶嵌的景观格局特征;20年内土地覆盖类型发生了显著的变化,景观异质性增强.基于研究区景观的高度破碎化,绘制小流域精细尺度土地覆盖图,高空间分辨率遥感数据十分必要.     

Does outmigration lead to land degradation? Labour shortage and land management in a western Nepal watershed

In Nepal, changing demographic patterns are leading to changes in land use. The high level of outmigration of men in the hills of Kaski District, Western Development Region of Nepal, is affecting the household structure but also land management. Land is often abandoned, as the burden on those left behind is too high. How do these developments affect the state of the land in terms of land degradation? To find out, we studied land degradation, land abandonment caused by outmigration, and existing sustainable land management practices in a subwatershed in Kaski District. Mapping was done using the methodology of the World Overview of Conservation Approaches and Technologies (WOCAT). While previous studies expected land abandonment to exacerbate slope erosion, we demonstrate in this paper that it is in fact leading to an increase in vegetation cover due to favourable conditions for ecosystem recovery. However, negative impacts are several, including the increase of invasive species harmful to livestock and a decline in soil fertility. Traditional land management practices such as terraces and forest management exist. To date, however, these measures fail to take account of the changing population dynamics in the region, making the question of how migration and land degradation are linked worth revisiting.     

Land use changes and trends in Human Appropriation of Above Ground Net Primary Production (HANPP) in India (1961–98)

Land use change has the potential to influence energy flows, standing crop and biomass turnover at a variety of scales. To understand and quantify the impact of land use change on natural systems, interdisciplinary approaches and concepts linking biophysical and socioeconomic factors are needed. One such approach for analysing the socioeconomic energy flows from land use changes is Human Appropriated Net Primary Production (HANPP). HANPP is defined as the difference between the net primary production of potential vegetation and the actual net primary production remaining in vegetation after harvest. In this study, we used HANPP to quantify the energy flows consequent upon land use/land cover change from 1961 to 1998 in India. Data from the Food and Agricultural Organization Statistics (FAOSTAT) covering land use/land cover estimates, crop production, harvest and fertilizer use data have been used to analyse the trends in HANPP. Land use changes between 1961 and 1998 indicate a small increase in agricultural areas from 58.2% to 60.8% and in forest and woodland areas from 19.0% to 23.2%. Actual above ground net primary production of vegetation increased from 1280.58 to 1818.23 Tg, an increase of approximately 1.4 times over 37 years. Although population increased exponentially, human appropriation of photosynthetic products did not rise as much due to increases in forest cover and agricultural production. Although the HANPP concept is a useful approach to analyse the trends in photosynthetic products brought about by land use changes and harvesting, more robust indicators are needed to understand the impacts associated with these changes. We discuss the relevance of the HANPP analysis results by focusing on land use/land cover change and exploring the inter-linkages between energy flows and environment.     

科尔沁沙质草地植物群落的放牧退化及其自然恢复过程

 为了了解不同放牧强度对我国北方沙质草地的影响及其封禁停牧后草地植被的自然恢复过程,我们于1992—2006年在科尔沁沙地开展了草地放牧和封育试验,分析研究了人类放牧活动对草地植被的影响,比较了不同程度退化草地恢复速度及其所受气候变化影响。研究结果表明:①在科尔沁沙地,随着放牧强度的增加,草地植被受放牧影响的程度会加重,但只有持续重牧才会导致植被的严重退化,而且持续重牧对植被盖度、高度和草地生产力的危害程度要大于对物种丰富度和多样性的危害程度;中度放牧可以导致植被盖度、高度、生物量的轻度下降,但对物种丰富度、多样性没有不良影响;对于退化草地而言,持续轻牧可促进植被的有效恢复;②封禁停牧以后,草地原受干扰程度不同,其恢复的相对速度也不同,表现为原草地退化越严重,其恢复速度相对越快,而且是植被高度、盖度、生物量的恢复速度要大于物种丰富度、多样性和频度的恢复速度;③草地植被的恢复演替明显受到气候变化的影响,暖湿气候有利于植被的恢复,暖干气候对于植被的恢复不利。     

Qualitative satellite image analysis: Mapping spatial distribution of farming types in Ethiopia

Satellite images have enormous potential for qualitative land use analysis. This paper presents empirical results that demonstrate how normally invisible dimensions produced by land use can be identified by enriching satellite data with qualitative information from field studies.Land use can be defined as the intentional use of a specific piece of land resulting in patterns of ecological responses that are visible in the land cover and landscape. Responses to land use often result in a heterogeneous combination of reflectance in satellite images. Statistical methods used in the classification of satellite imagery are limited in their capacity to handle categories consisting of heterogeneous combinations of spectral values. To overcome this limitation, a contextual post-classification method has been used to map land cover configurations as related to different agricultural practices in the district of Sodo, Ethiopia.The results show that it is possible to map socio-spatial distribution of different agricultural and socioeconomic practices on a regional level by combining field observations and spatial contextual information. The empirical findings show local agricultural activity variations in cash crop production and subsistence agriculture in the Sodo district of Ethiopia.     

放牧强度对科尔沁沙地沙质草地植被的影响

为了研究科尔沁沙地沙质草地在不同放牧强度下植被特征的变化规律,比较了围封、中度放牧、重度放牧3种条件下的植被盖度、群落组成、物种多样性、地上/地下生物量和凋落物量等植被特征的变化特征。结果表明:(1)围封、中度放牧和重度放牧沙质草地的优势植物均为一年生植物,但围封和中度放牧中多年生禾本科植物优势度高于重度放牧,重度放牧沙质草地一年生植物所占优势度最大;(2)放牧强度对沙质草地植被盖度、地上生物量及凋落物量有显著影响。随着放牧强度的增加,植被盖度、地上生物量和凋落物量均降低;(3)围封、中度放牧和重度放牧沙质草地物种丰富度及多样性差异均不显著;(4)放牧强度和土壤深度及其交互作用均能影响地下生物量。随着放牧强度的增加,总的地下根系生物量减小。而重度放牧草地中, 3个土壤深度间地下根系生物量差异不显著。放牧改变了沙质草地植物群落的组成、极大降低了植被盖度和生产力;尤其是重度放牧急剧增加了一年生植物的优势、且对浅层根分布的减少影响最大。     

基于线性光谱分离技术的西藏乃东县土地覆被变化监测

青藏高原是全球气候变化研究关注的热点地区,也是中国生态保护的重点区域,其土地覆被变化研究对优化土地利用结构、改善土地覆被状况和生态环境具有重要意义。线性光谱分离技术是利用遥感手段监测土地覆被变化的有效方法。本文选取西藏乃东县为研究区,利用1988、2000和2010年三期Landsat TM、ETM遥感影像,采用线性光谱分离技术,定量提取了研究区三期影像中单个像元的植被、裸土、裸岩覆被率比例,同时将植被分量与NDVI结果进行对比分析。结果表明：①研究区山峦重叠,沟谷纵横,地表破碎,混合像元比例高,线性光谱分离技术可以很好地处理复杂地物的土地覆被变化;②1988-2010年间,研究区裸土面积下降幅度较大,植被覆盖率及裸岩覆盖率有所上升,说明本区植被得到一定的恢复,但同时石漠化也在进一步加剧;③通过对线性光谱分离的植被分量与NDVI结果比较,发现线性光谱分离技术对青藏高原土地覆被识别具有较好的适用性。