Land Cover Transition in Northern Tanzania

Land conversion in sub‐Saharan Africa has profound biophysical, ecological, political and social consequences for human well‐being and ecosystem services. Understanding the process of land cover changes and transitions is essential for good ecosystem management policy that would lead to improved agricultural production, human well‐being and ecosystems health. This study aimed to assess land cover transitions in a typical semi‐arid degraded agro‐ecosystems environment within the Pangani river basin in northern Tanzania. Three Landsat images spanning over 30 years were used to detect random and systematic patterns of land cover transition in a landscape dominated by crop and livestock farming. Results revealed that current land cover transition is driven by a systematic process of change dominated by the following: (i) transition from degraded land to sparse bushland (10·8%); (ii) conversion from sparse bushland to dense bushland in lowland areas (6·0%); (iii) conversion from bushland to forest (4·8%); and (iv) conversion from dense bushland to cropland in the highlands (4·5%). Agricultural lands under water harvesting technology adoption show a high degree of persistence (60–80%) between time slices. This suggests that there is a trend in land‐use change towards vegetation improvement in the catchment with a continuous increase in the adoption of water harvesting technologies for crop and livestock farming. This can be interpreted as a sign of agricultural intensification and vegetation regrowth in the catchment. Copyright © 2015 John Wiley & Sons, Ltd.     

Sustainable agricultural development in sub-Saharan Africa: the case for a paradigm shift in land husbandry

In order to tackle poverty and hunger in sub‐Saharan Africa (SSA) there is a strong case for a focus of effort on improving rainfed agricultural systems. The challenge is to deliver a transformation of agricultural productivity in such systems without adverse impacts on environmental goods and services. We examine the growing advocacy of ‘conservation agriculture’ (CA) as the desired approach and assess the evidence to support the assertion that it can deliver sustainable agricultural development in SSA. We examine in particular the evidence which derives from experience with ‘zero tillage sustainable agriculture’ in Brazil. We ask the question, is there a case for a paradigm shift in land husbandry? The case for a paradigm shift hangs on the premise that conventional practice promotes land degradation, while adoption of CA practice delivers a range of benefits through promoting soil ecosystem health. The guiding principle is to promote biological tillage through minimizing mechanical soil disturbance and maintaining permanent organic soil cover. We examine evidence of benefits in the context of the wider debate on low‐external‐input technology. We conclude that CA does not overcome constraints on low‐external‐input systems and will deliver the productivity gains that are required to achieve food security and poverty targets only if farmers have access to fertilizers and herbicides. We conclude also that widespread adoption of the new paradigm amongst millions of small farmers in order to achieve the ‘doubly green revolution’ in SSA is subject to the familiar constraints of knowledge transfer and success will depend upon creating innovation networks. Further, we conclude that amongst small‐scale farmers partial adoption will be the norm and it is not clear that this will deliver soil health benefits claimed for full adoption of the new paradigm.     

天生桥一级水库蓄水前后库周土地覆盖变化研究

采用天生桥一级水电站水库库周1987年和2002年两景TM遥感影像,进行建库前后土地覆盖变化分析,绘制出相应的土地利用图。通过FRAGSTATS方法,对7个有代表性的景观空间结构与异质性的定量指标进行计算,研究了该区域景观生态结构与景观格局变化。研究结果表明,天生桥一级水电站的建设对周围的土地覆盖影响不大,建库前分布最广的灌丛面积从1987年的33%减少至2002年的20%,而草地由1987年的31%增至2002年的39%,成为建库后覆盖面积最广的土地利用类型。但在1987～2002年的15年间,景观空间     

锡林浩特市土地利用/覆盖变化研究

利用1995年和2000年的土地利用/覆盖数据,对锡林浩特市的土地利用/覆盖变化进行了研究。结果表明:1995—2000年间,锡林浩特草场资源退化趋势明显,高覆盖度草场明显减少,中、低覆盖度草场以及未利用地不断增加,草场资源向着恶性方向发展。此外,城镇扩展,毁草开荒等人类活动也破坏了大量优质草场。由于人类的不合理利用,研究区的景观格局日益破碎化,其中草地景观要素破碎化明显。草地资源是锡林浩特市社会经济发展和生态环境建设的关键,其不断退化和破碎已经成为严重社会经济和生态环境问题,影响着该区农牧业的正常生产和生态环境的持续发展,急需解决。     

Field‐Based screening methodology to improve tolerance of common bean to low‐P soils

Abstract

Phosphorus (P) limits common bean (Phaseolus vulgaris L.) production throughout sub‐Saharan Africa, where P fertilizer is not affordable to the vast majority of smallholder farmers. Genetic differences in bean performance in low‐P soils suggest that low P tolerance could be improved. Earlier breeding efforts have not been successful, in part due to the challenges of selecting genotypes with improved performance in a heterogeneous soil environment. A field based screening method for low P tolerance has been developed, based on evaluating soil status and ameliorating edaphic compounding factors. The soil is classified as an Oxic Haplustalf and is representative of the unimodal, mid‐to‐high altitude bean growing regions of Southern Africa. The soil has very low zinc (Zn) and nitrogen (N) contents, which reduced growth markedly. After amelioration of these edaphic complications, P response could be quantified. A promising genotype CAL 143 was selected which consistently expressed, over two growing seasons, low P tolerance and high yield responsiveness to moderate fertilizer P application.     

中国北方13省土地利用景观格局变化分析(1989～1999)

以北方13省为研究区，对该区1989～1999年的宏观土地利用景观格局变化进行了分析。结果表明：决定该区景观格局的主体要素类型为草地、难利用地和林地．其次为耕地。1989～1999年期间，区内景观异质性程度在逐渐提高．土地利用向着多样化和均匀化方向发展。景观空间格局变化特征是：耕地、林地和城镇用地破碎度最大；林地、草地和水域受到人类活动的严重干扰．斑块空间分布不断分散和破碎化．分离度和破碎度指标增加。草地的破碎度增加最为显著，严重影响该区农牧业的正常生产。景观要素之间的转化关系主要表现为林、草地和耕地之间的相互转化．以及草地退化为难利用地。表征了该区生态建设实践和生态破坏活动的相互作用以及草地的严重退化趋势．说明北方13省存在较为严重生态环境问题．急需解决。     

Land use/cover change and landscape fragmentation analysis in the Bindura District,Zimbabwe

Rapid land use/cover change and landscape fragmentation is occurring in many countries in central and southern Africa, as a result of colonial imbalances in land distribution, demographic pressure, agricultural expansion, government policies and environmental factors such as drought. This study analysed the dynamics of land use/cover and land degradation as revealed in landscape fragmentation in the Bindura District of Zimbabwe based on Landsat data for 1973 and 2000. A hybrid supervised/unsupervised classification approach coupled with GIS analyses was employed to generate land use/cover maps from which various class level landscape metrics were calculated using FRAGSTATS®, in order to analyse landscape fragmentation. The results show that agriculture, mixed rangeland, settlements, bareland and water increased, while woodland areas decreased. Consequently, the landscape became more highly fragmented as indicated by an increase in the patch number and a decrease in the mean patch size (MPS) of the woodland and mixed rangeland classes. This suggests that anthropogenic activities driven by agricultural expansion were the main causes of landscape fragmentation, leading to landscape degradation in the study area. Copyright © 2006 John Wiley & Sons, Ltd.     

Assessing land degradation in the Monduli District,northern Tanzania

One of the many contentious issues facing the appropriate and accurate assessment of land degradation is the varying emphasis placed on vegetation degradation and soil degradation processes. This has led to the compartmentalization of land degradation assessment methods, depending on the particular perspective adopted. The land degradation assessment method presented here attempts to take into account both vegetation and soil degradation. This methodology is applied to the southern part of the Monduli District of northeast Tanzania, an area typifying the so‐called ‘affected drylands’ of Africa. Three sets of land cover maps synchronized against long‐term rainfall data (1960s, 1991 and 1999) were used to assess land degradation in the area. Utilizing these three sets of land cover maps as a basis for change detection, it is possible to distinguish areas that experienced changes in vegetation due to rainfall variability from those areas that were subject to changes consequent upon anthropological factors. All areas that displayed overall depletion of natural and semi‐natural vegetation due to human factors were deemed to have undergone land degradation, whereas areas that experienced inter‐annual land cover changes due to rainfall variability were classified as experiencing cover change due to ecosystem dynamics. This method provides a complete and appropriate assessment of land degradation in the study area and can be used to improve degradation assessment in other semiarid areas. Copyright © 2006 John Wiley & Sons, Ltd.     

Tobacco cultivation as a driver of land use change and degradation in the miombo woodlands of south‐west Tanzania

Miombo woodlands support agriculture, biodiversity, and multiple ecosystem services across an extensive part of sub‐Saharan Africa. Miombo is frequently overutilised with deforestation and degradation resulting in significant land use and land cover change (LULCC). Understanding the drivers of LULCC is essential to achieving sustainable land management in miombo woodland regions. Within a remote miombo area of south‐west Tanzania in the Kipembawe Division, Mbeya Region, social survey and ecological data were used to identify the direct and indirect drivers of LULCC. Our findings show that tobacco (Nicotiana tabacum ) production results in an estimated annual deforestation rate of 4,134 ± 390 ha of undisturbed miombo woodland, of which 56.3 ± 11.8% is linked to the post‐harvest curing process. This deforestation represents 0.55 ± 0.06% of the wooded area of the Kipembawe Division. The perception of high incomes from tobacco cultivation has encouraged migration of both agriculturalists and pastoralists into the area, resulting in higher livestock numbers that lead to further degradation. Higher human populations need more woodland resources such as fuelwood and building materials and more farmland for food crops. Continued deforestation will reduce the long‐term profitability of tobacco cultivation due to a lack of fuel to cure the crop and could render production unviable. Action is urgently needed to conserve globally important biodiversity resources while enabling agricultural and pastoral activities to continue. Improved governance, together with sustainable land management strategies and diversification of livelihood strategies, can reduce dependence on tobacco cultivation and contribute to a sustainable future for this ecoregion.     

西藏普兰县土地覆被景观分析

结合RS和GIS提取西藏普兰县土地覆被类型,以FRAGSTATS提取主要景观指数,运用生态位态势理论,对县域的农业、林业、牧业三大主要覆被景观的经济生态位与景观结构生态位进行了评价分析。结果表明,普兰县以裸岩为基质景观,维持全县生物多样性及生态系统健康的主要是草地与灌木林地景观;生态位态势理论对土地覆被景观的评价体现出了自然和人为作用下,各种土地覆被景观在县域内所形成的不同生态和经济地位;普兰县裸岩的景观生态位最高,它在全县所占面积比例最大决定了其生态最稳,耕地半自然景观在有人为合理干扰条件下,在具有最低的景观结构生态位基础上却能产生较高的经济效益。     

Runoff Trends Driven by Climate and Afforestation in a Pyrenean Basin

The abandonment of traditional rural life in mountain areas has favoured the expansion of forest in the headwaters of Pyrenean rivers. In this paper, we (i) analyse hydro‐climatic trends at the annual and monthly scales in three nested sub‐catchments in a central Pyrenean basin and (ii) quantify the relative contribution of climate change and forest cover on the observed changes in runoff. Land use maps indicate an increase in the forest cover in all sub‐basins for the period 1987–2009. Non‐parametric Mann–Kendall statistic on annual and monthly hydro‐climatic data from 1965 to 2009 was used to identify trends in climate and runoff data. To assess the potential influence of the period length, trends were also examined for the 1941–2009 stretch. Upward trends were detected for temperature and potential evapotranspiration, particularly during summer and winter months. Precipitation trends and their significance depended on the length of the period considered, although overall results indicated a decrease, particularly for February and July. The effects of climate change and land cover change on annual runoff were identified by means of a change point analysis. Results indicated that a change in annual runoff took place in the 1980s, suggesting the non‐linearity in the relationship between precipitation and runoff, and thus the influence of land use factors. The influence of forest cover was confirmed by comparing observed runoff trends with those resulting from a hydro‐climatic model that does not take into account land use changes. Divergence between both trends revealed that forest cover can account for ~40% of the observed decrease in annual runoff. Copyright © 2015 John Wiley & Sons, Ltd.     

Historical influences on the vegetation and soils of the Martha’s Vineyard, Massachusetts coastal sandplain: Implications for conservation and restoration

Both disturbance history and previous land use influence present-day vegetation and soils. These influences can have important implications for conservation of plant communities if former disturbance and land use change species abundances, increase colonization of nonnative plant species or if they alter soil characteristics in ways that make them less suitable for species of conservation interest. We compared the plant species composition, the proportion of native and nonnative plant species, and soil biogeochemical characteristics across seven dominant land use and vegetation cover types on the outwash sandplain of Martha’s Vineyard that differed in previous soil tillage, dominant overstory vegetation and history of recent prescribed fire. The outwash sandplain supports many native plant species adapted to dry, low nutrient conditions and maintenance of native species is a management concern. There was broad overlap in the plant species composition among pine (Pinus resinosa, P. strobus) plantations on untilled soils, pine plantations on formerly tilled soils, scrub oak (Quercus ilicifolia) shrublands, tree oak (Q. velutina, Q. alba) woodlands, burned tree oak woodlands, and sandplain grasslands. All of these land cover categories contained few nonnative species. In contrast, agricultural grasslands had high richness and cover of nonnative plants. Soil characteristics were also similar among all of the woodland, shrubland and grassland land cover categories, but soils in agricultural grasslands had higher pH, extractable Ca²⁺ and Mg²⁺ in mineral soils and higher rates of net nitrification. The similarity of soils and significant overlap in vegetation across pine plantations, scrub oak shrublands, oak woodlands and sandplain grasslands suggests that the history of land use, current vegetation and soil characteristics do not pose a major barrier to management strategies that would involve conversion among any of these vegetation types. The current presence of high cover of nonnative species and nutrient-enriched soils in agricultural grasslands, however, may pose a barrier to expansion of sandplain grasslands or shrublands on these former agricultural lands if native species are not able to outcompete nonnative species in these anthropogenically-enriched sites.     

IMPACTS OF LAND COVER CHANGE SCENARIOS ON STORM RUNOFF GENERATION: A BASIS FOR MANAGEMENT OF THE NYANDO BASIN,KENYA

The effects of conceptual land cover change scenarios on the generation of storm runoffs were evaluated in the Nyando Basin. The spatial scenarios represented alternatives that vary between full deforestation and reforestation. Synthetic storm events of depths 40, 60 and 80 mm were formulated according to the rainfall patterns and assumed to have durations corresponding to the runoff times of concentration. The Natural Resource Conservation Service–Curve Number model was used to generate runoff volumes within the sub‐catchments, which were subsequently routed downstream to obtain effects in the whole basin. The simulated land cover change impacts were evaluated relative to values obtained from the actual land cover state of the basin in the year 2000. From the results, an agricultural land cover scenario constituting of about 86 per cent of agriculture indicated increased runoff volumes in the entire basin by about 12 per cent. An agricultural‐forested land cover scenario with 40 and 51 per cent of forest and agriculture respectively revealed reduced runoff volumes by about 12 per cent. Alternatively, a scenario depicting a largely forested land cover state with about 78 per cent of forests reduced the runoff volumes by about 25 per cent according to the model estimates. Runoff volumes in the basin were also likely to reduce by about 15 per cent if the appropriate land cover scenario for the respective sub‐catchments were to be assumed for runoff management purposes. Considering the prevalent data uncertainty, the study effectively highlights the potential hydrological vulnerability of the basin. The results obtained can form a basis for appropriate catchment management of the area. Copyright © 2012 John Wiley & Sons, Ltd.     

三峡库区开县蓄水前后景观格局变化特征

三峡工程是世界上举世瞩目的大型水电水利工程,其建成后具有巨大的综合效益,但水库蓄水完成后,也引起库区内的土地覆被与景观格局的变化。为了及时掌握水库蓄水后库区土地覆被及景观格局变化情况,该文以三峡库区重庆市开县为研究对象,基于2002、2007和2010年3期遥感影像资料,运用遥感与GIS技术和景观格局分析方法,利用ArcGIS9.3、Ecognition8.0、Fragstats3.3等软件分析了研究区土地覆被与景观格局动态变化特征。研究表明:由于受2002-2010年间水库蓄水影响,开县土地覆被与景观格局均有剧烈变化。该地区景观优势类型是森林、灌木、旱地、草地和水田。景观类型水平上,旱地、水田、草地景观面积减少且破碎度增加,但森林、水体、建设用地面积增加,同时连通性增加;景观格局水平上,景观总体破碎度增加,景观优势度降低,但景观多样性增加,有利于该地区生态系统稳定。开县2002-2007年和2007-2010年2期景观格局变化表现出不同的特征。研究结果及时反应了水库蓄水前后的土地覆被与景观格局变化特征,为水库未来土地利用合理规划与生态景观设计提供依据。     

Grassland decline in Kinangop Plateau, Kenya: implications for conservation of Sharpe's longclaw (Macronyx sharpei)

The Kinangop highland grasslands, the world stronghold of the endangered Sharpe's longclaw (Macronyx sharpei), consist almost entirely of privately owned land. As human population in the grasslands increases, the mean acreage of land holdings decreases and more grassland is being converted to other uses. Land subdivision information, existing human population data, and current land use data from a subset of 162 farms were used to extrapolate the past and future extent of Sharpe's longclaw habitat throughout the landscape on Kinangop Plateau. It was estimated that grasslands covered 50% of the plateau in 2000, but only 58% of the grassland area was likely to be tussock grasslands, the preferred habitat of Sharpe's longclaw. Large farms are being subdivided rapidly, and more than half of the remaining tussock grasslands are likely to be found on farms that are not large enough to support large longclaw territories. We predict that by 2010 tussock grasslands will cover only one-fifth of Kinangop, and all farms that are large enough to act as longclaw reserves are likely to have been subdivided. We propose urgent prioritisation of a network of large farms (>30 ha) for conservation action.     

Analysing resilience in dryland agro‐ecosystems: a case study of the Makanya catchment in Tanzania over the past 50 years

Dryland agro‐ecosystems in sub‐Saharan Africa provide the resource base for some of the fasted growing populations today. However, rainfall variability and poor soils make these systems inherently vulnerable, and land degradation reduces their capacity to cope with disturbances. In this paper we propose a theoretical framework for interpreting dynamics and resilience in such systems, where two aggregate variables, the agricultural soil water index and the ecosystem insurance capacity, are particularly important. We apply the framework to the case of the Makanya catchment in Tanzania and conclude that the studied area has moved towards an increasingly degraded state, where ecosystem services other than food have been lost, over the past 50 years. Three main drivers behind this are identified; a) institutional changes affecting strategies for natural resource management, b) increased dry‐spell frequency, and c) high population growth. We suggest that the reason for the dramatic effects is that these changes occurred simultaneously, reducing the adaptive capacity of the local population. However, several trends in the area today indicate that there is a window of opportunity for positive change. Copyright © 2007 John Wiley & Sons, Ltd.     

1986-2013年南京市土地利用/覆被景观格局时空变化及驱动力因素分析

以南京市为研究对象,采用南京市1986年、1996年、2002年、2013年的四期土地利用/覆被数据,运用景观生态学原理,借助ArcGIS软件和Fragstats软件,从土地利用类型结构、变化速度、转化关系和景观格局等方面分析南京市近30年土地利用/覆被和景观格局的时空变化状况及其驱动因素。结果表明:（1）南京市近30 a中土地利用/覆被发生了剧烈变化,耕地在整个研究区起到主导作用,其面积比例均在48%以上,但是其优势度逐渐降低,大量自然景观向人为景观转变是研究区土地利用变化最显著的特征;（2）整体景观类型变化速度都在增大,而草地和其他用地变化最为活跃,林地相对最稳定,土地利用结构处于快速调整阶段;（3）耕地的转出最大,主要转向为居民点及建设用地;（4）景观格局变化明显,破碎化程度越来越高,景观格局趋向复杂化,景观结构不稳定性增加;（5）人口增长、经济发展、区域政策和城市规划等共同推动了研究区景观格局的变化。该研究结果对于南京市的科学规划及可持续发展提供重要参考。     

Evaluating land use/land cover changes and fragmentation in the Camili forest planning unit of northeastern Turkey from 1972 to 2005

Changes in land use/land cover have important consequences on the management of natural resources including soil and water quality, global climatic systems and biodiversity. This study analysed the spatial and temporal pattern of land use/land cover change in the Camili forest planning unit that includes the Camili Biosphere Reserve Area within the Caucasian hotspot, in the northeast corner of Turkey. To assess the patterns during a 33‐year period, the necessary data were obtained from forest stand maps and evaluated with Geographic Information Systems and FRAGSTATS. Results showed that the total forested areas increased from 19 946·5 ha (78·6% of the study area) in 1972 to 20 797·3 ha (81·9 per cent) in 2005 with a slight net increase of 851 ha. Softwood cover types (411·8 ha) completely transitioned to other cover types over 33‐year period. In terms of spatial configuration, the total number of forest fragments increased from 172 to 608, and mean size of forest patch (MPS) decreased from 147·7 ha to 41·8 ha during the period. Nearly 84 per cent of the patches in 1972 and 93 per cent of them in 2005 generally seem to concentrate into 0–100 ha patch size class, indicating more fragmented landscape over time that might create a risk for the maintenance of biodiversity of the area. There were apparent trends in the temporal structure of forest landscape, some of which may issue from mismanagement of the area, social conflict, and illegal utilization of forest resources due to ineffective forest protection measurements. The study revealed that it is important to understand both spatial and temporal changes of land use/land cover and their effects on landscape pattern to disclose the implications for land use planning and management. Copyright © 2007 John Wiley & Sons, Ltd.     

黄土区大型露天矿农业用地格局演变的分析

在矿区废弃地的恢复中，格局变化的研究将对矿区生态系统的变化起着至关重要的作用。其中，农业用地格局演变的过程及覆被类型的变化，对矿区的生态安全、耕地保护及土地资源可持续利用具有重要的现实意义。该文以山西平朔矿区为例，基于GIS平台，在分析矿区土地动态变化的基础上，运用景观生态学理论与方法，对平朔矿区景观动态变化过程、特征及覆被类型的变化进行了研究，特别对矿区农用地的变化做了重要分析，结果表明：大型露天矿区生态系统景观动态变化过程包括生态破坏过程的景观变化(土地挖损、土地压占、土地占用)和生态重建过程的景观变化(地貌重塑、土壤重构、植被重建)；经过20年的人工控制的生态重建后，矿区土地利用空间格局由以旱地—疏林地格局演变为以林地—建设用地为主的重建生态格局；矿区生态重建已经改变了原脆弱生态系统的生态环境，其中农业用地增加了50%，但由于管理制度等原因，复垦的农用地目前大部分尚不能转换为耕地使用。     

Rangeland development of the Mu Us Sandy Land in semiarid China: an analysis using Landsat and NOAA remote sensing data

Degradation of the dry semiarid ecosystems in the Mu Us Sandy Land of north central China was explored using high‐resolution satellite images from 1978, 1987 and 1996. This study monitored both changes in grassland biomass production and reclamation activities to detect the nature and scale of land degradation since major economic reforms were introduced in 1978. The position of the high‐resolution images within the vegetation cycles was inspected from National Oceanographic and Atmospheric Administration (NOAA) NDVI images at 10‐day repetition and seasonal precipitation patterns. A model was developed to categorize changes in the vegetation signal activity from 30 × 30 m pixels into vegetation cover development and land‐use changes between 1987 and 1996. A general increase of biomass production was evident despite the rapid increase in numbers of grazing animals. This increase in biomass was confirmed by the NOAA time series, which also revealed annual variability related to the amount and pattern of the seasonal rains. Rangeland conversion to farmland was detected, and this process has increased the area of cultivation almost fivefold. The classified area of cultivation corresponds with reported statistical records, also showing that irrigation features in virtually 100 per cent of the sown area. Signs of declining biological production, indicating land degradation processes, are few. Biomass production has increased, with a gain in the economic output from both crop and animal production. The early start of active measures to halt desertification has increased vegetation cover and lowered wind erosion potential and grasslands seems to be managing the high levels of grazing pressure. Copyright © 2003 John Wiley & Sons, Ltd.