Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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Trait-based approaches for guiding the restoration of degraded agricultural landscapes in East Africa
Lohbeck, Madelon ; Winowiecki, Leigh ; Aynekulu, Ermias ; Okia, Clement ; Vågen, Tor Gunnar - \ 2018
Journal of Applied Ecology 55 (2018)1. - ISSN 0021-8901 - p. 59 - 68.
agricultural land - agroecology - agroforestry - erosion - functional diversity - functional traits - land degradation - soil health - soil organic carbon - vegetation
Functional ecology provides a framework that can link vegetation characteristics of various land uses with ecosystem function. However, this application has been mostly limited to [semi-]natural systems and small spatial scales. Here, we apply functional ecology to five agricultural landscapes in Kenya, Uganda and Ethiopia, and ask to what extent vegetation characteristics contribute to soil functions that are key to farmers’ livelihoods. We used the Land Degradation Surveillance Framework (LDSF), a multi-scale assessment of land health. Each LDSF site is a 10 × 10 km landscape in which vegetation cover and erosion prevalence were measured, a tree inventory was carried out, and topsoil (0–20 cm) samples were collected for organic carbon (SOC) analysis in approximately 160 × 1,000 m2 plots. Land degradation is a recurring phenomenon across the five landscapes, indicated by high erosion prevalence (67%–99% of the plots were severely eroded). We used mixed models to assess if vegetation cover, above-ground woody biomass and the functional properties of woody vegetation (weighted-mean trait values, functional diversity [FD]) explain variation in SOC and erosion prevalence. We found that the vegetation cover and above-ground biomass had strong positive effects on soil health by increasing SOC and reducing soil erosion. After controlling for cover and biomass, we found additional marginal effects of functional properties where FD was positively associated with SOC and the abundance of invasive species was associated with higher soil erosion. Synthesis and applications. This work illustrates how functional ecology can provide much-needed evidence for designing strategies to restore degraded agricultural land and the ecosystem services on which farmers depend. We show that to ensure soil health, it is vital to avoid exposed soil, maintain or promote tree cover, while ensuring functional diversity of tree species, and to eradicate invasive species.
Getting a grip on hydrological and sediment connectivity
Masselink, Rens J.H. - \ 2017
University. Promotor(en): Coen Ritsema; Sjoerd van der Zee, co-promotor(en): Saskia Keesstra; Arnaud Temme. - Wageningen : Wageningen University - ISBN 9789463436342 - 158
hydrology - sediment - land degradation - slopes - geological sedimentation - land management - soil physics - hydrologie - landdegradatie - hellingen - geologische sedimentatie - grondbeheer - bodemfysica

Land degradation is a large problem worldwide, especially in agricultural areas. Between 1-6 billion ha of land worldwide is affected by land degradation. With an increasing world population, more food production is needed and, therefore, more land is converted into agricultural areas. This conversion of land to agricultural areas, in turn, leads to more land degradation. Some common forms of land degradation are desertification, salinization and soil erosion by water. The negative effects of soil erosion have been recognized for a long time. Since the early 20th century, researchers have tried to quantify soil displaced due to water, and to measure and model the efficiency of management strategies.

The implications of problems with upscaling, wrong process representation and equifinality include the difficulty to properly predict sediment sources, pathways and sinks within catchments. These problems then can translate into the implementation of sub-optimal management strategies. To deal with these non-linear processes and the lack of proper representation of water and sediment sources, pathways and sinks, the concept of connectivity was developed. Currently, many definitions of connectivity have been proposed, although the definition most used is that of hydrological connectivity by Pringle (2003): ‘Hydrologic connectivity is the water-mediated transport of matter, energy and organisms within or between elements of the hydrologic cycle’.

A unified theory on what constitutes connectivity and how connectivity should be measured or inferred remains one of the biggest challenges within catchment science. In addition, it is unclear whether connectivity should be an output or an input of a model and if an input, whether this should be added explicitly or implicitly. The main objective of this thesis was, therefore, to assess and quantify hydrological and sediment connectivity in a meaningful way, which can further our understanding of hydrological and sediment transport processes and catchment system dynamics.

The study was carried out in three catchments in Navarre, northern Spain. Two catchments, ‘Latxaga’ and ‘La Tejeria’, are agricultural catchments with sizes of 2.07 km2 and 1.69 km2, respectively. The ‘Oskotz Forestal’ catchment is a (semi-)natural catchment, with a size of 5.05 km2. Land cover in the agricultural catchments is mainly winter wheat and barley, while in the Oskotz catchment it is grassland and forest. Latxaga and La Tejeria are mainly underlain by marls and within La Tejeria some sandstone is also present. The geology in Oskotz is characterised by an alternation of marls and sandy limestone.

In chapter 2, I used networks (graph theory) to characterise and quantify overland flow connectivity dynamics on hillslopes in a humid sub-Mediterranean environment by using a combination of high-resolution digital-terrain models, overland flow sensors and a network approach. Results showed that there are significant differences between overland flow connectivity on agricultural areas and semi-natural shrubs areas. Significant positive correlations between connectivity and precipitation characteristics were found. Significant negative correlations between connectivity and soil moisture were found, most likely due to soil water repellency and/or soil surface crusting. The combination of structural networks and dynamic networks for determining potential connectivity and actual connectivity proved a powerful tool for analysing overland flow connectivity.

In chapter 3, I determined the functioning of hillslope-channel connectivity and the continuation of transport of these sediments in the channel. To determine this functioning, I obtained data on sediment transport from the hillslopes to the channels while simultaneously looking at factors that influence sediment export out of the catchment. For measuring hillslope-channel sediment connectivity, Rare-Earth Oxide (REO) tracers were applied to a hillslope in the Latxaga catchment preceding the winter of 2014-2015. The results showed that during the winter there have been no sediments transported from the hillslope into the channel. Analysis of precipitation data showed that although total precipitation quantities did not differ much from the mean, the precipitation intensities were low. Using a Random Forest (RF) machine learning method, I showed that hillslope-channel connectivity in Latxaga is dominated by sediment mobilisation during large (high intensity) precipitation events. Sediments are for a large part exported during those events. Large events also leave behind large amounts of sediments in and near the channel, which is gradually removed by small events.

In chapter 4 I demonstrated that existing data can be used to assess governing factors of connectivity, and how these factors change over time. Data from three catchments in Navarre, Northern Spain, were used to assess factors that influence hydrologic and sediment connectivity. These factors were used as components in a spatially-lumped linear model for discharge and suspended-sediment yield. Three components of connectivity were distinguished: topographical, biological and soil. Changes in the topographical component for the studied periods were considered relatively small, and, therefore, kept constant. Changes in the biological component were determined using the Normalised Difference Vegetation Index. Changes in the soil component were assessed using an Antecedent Precipitation Index. Nash-Sutcliffe model efficiency coefficients were between 0.49 through 0.62 for the discharge models and between 0.23 through 0.3 for the sediment-yield models. I recommended applying the model at smaller spatial scales than catchment scale to minimize the lumping of spatial variability in the components.

In chapter 5, the objective was to better understand the implications of model calibration at different spatial scales on the simulation of hydrology and sediment dynamics of an agricultural catchment. I applied the LAPSUS-D model to the Latxaga catchment. The model was calibrated and validated (4 years: 2011-2015) using three datasets at varying spatial scales: hillslope, catchment and the combined dataset (combined-calibrated model). The hillslope-calibrated model showed mainly infiltration-excess overland flow, the catchment-calibrated mainly saturation-excess overland flow at the footslopes and the combined-calibrated model showed saturation-excess overland flow from the midslopes to the footslopes. For hydrology, the combined-calibrated model simulated the large discharge peaks best, while at the hillslope scale, the hillslope-calibrated model performed best. The hillslope-calibrated model produced the highest model efficiencies for sediments, for calibration (0.618) and validation (0.269). The hillslope-calibrated model was the only model that showed observed gully erosion on a high-resolution DEM and displayed channel sediment dynamics. However, absolute quantities of erosion and deposition within the catchment were too high. The results show that modellers need to be aware of problems associated with automatic calibration, over-calibration and not incorporating measured data at multiple spatial scales. We advocate incorporating runoff and sediment tracing data at multiple scales whenever this is possible and to, furthermore, carry out specific measuring campaigns towards this end, ultimately to get a more comprehensive view on hydrological and sediment connectivity within a catchment.

The combination of chapters in this thesis showed that the connectivity concept is useful for a wide range of studies, from hillslope scale to catchment scale. Using the concept, I was able to determine sediment dynamics for a humid-Mediterranean catchment and show that this behaviour is different than previously thought.

Depending of the aim of the study, various concepts of connectivity are useful. Different geologic and climatic settings cause large differences in catchment (sediment) dynamics. It might, therefore, not be necessary, or even possible, to strive for a single, unifying conceptual framework for connectivity. Instead, a collection of frameworks for different settings should be developed. These frameworks should, however, always aim at helping to understand which measurements need to be taken and which type of models and indices should be used for that particular setting.

It is my honest opinion that connectivity is definitely a useful concept to advance our knowledge on water and sediment transport processes further. However, careful consideration is also required as this particular concept will not necessary provide the ultimate explanation and insights in dynamic behaviour within watersheds around the world. The gap between the different spatial and temporal scales is too complex to be bridged with a single concept like connectivity. However, the many studies about connectivity that will be published in the near future will be able to advance knowledge on water and sediment transport processes.

To Tree or Not to Tree : Cultural Views from Ancient Romans to Modern Ecologists
Holmgren, Milena ; Scheffer, Marten - \ 2017
Ecosystems 20 (2017)1. - ISSN 1432-9840 - p. 62 - 68.
ecosystem services - forest - grassland - land degradation - savanna - tree encroachment - visions of nature

Few things are more defining in a landscape compared to the absence or presence of trees, both in aesthetic and in functional terms. At the same time, tree cover has been profoundly affected by humans since ancient times. It is therefore not surprising that opinions about deforestation and colonization of landscapes by trees have always been strong. Although loss of forests is often lamented, there is also profound cultural affection for open landscapes including some that have been deforested in the past. Here we take a historical view on perceptions of changing tree cover, and subsequently argue that the current ecological literature on forest-savanna-grassland transitions is not immune to value-laden perspectives. So far, ecosystem science has not done enough to analyze the effects of tree cover changes on ecosystem services and indicators of human well-being. Until these analyses are done, debates about forested versus open landscapes will be clashes of values rather than scientific evaluations. We discuss how ecosystem science may contribute to developing this field.

A socioeconomic analysis of the zaï farming practice in northern Burkina Faso
Schuler, Johannes ; Voss, Anna ; Ndah, Hycenth Tim ; Traore, Karim ; Graaff, Jan de - \ 2016
Agroecology and Sustainable Food Systems 40 (2016)9. - ISSN 2168-3565 - p. 988 - 1007.
Adoption - conservation agriculture - food security - land degradation - livelihood

The zaï farming practice is a local adaptation of conservation agriculture to degraded semiarid areas and consists of restoring heavily crusted soils through small planting pits. This article analyzes the land use change and its impacts through the zaï farming practice in the northern part of Burkina Faso from a socioeconomic perspective, based on data gathered through two surveys in the Ouahigouya region. A survey among 101 farmers concentrated mainly on adoption rates and household characteristics. Later, 16 farmers from the first survey were interviewed with respect to their adoption of the zaï technique for soil restoration. Farm data was collected to cover the farms’ and households’ expenses and revenues for the year 2011. Material and labor input, as well as the obtained yields, were analyzed using the economic farm model OLYMPE. The results reflect the positive economic benefits of zaï cereal production at field and farm level when compared to conventional cultivation, but also point out the constraints to its further expansion. Despite higher input costs mostly related to external labor, the increased yields led to a more than three times higher gross margin per hectare for zaï millet (101,085 FCFA) than the conventional system (23,030 FCFA). Yet, the physically demanding intensive labor requirements during land preparation and implementation of the planting pits (+117 % man days/ha) challenge a broader adoption of the zaï practice. Nonetheless, in a mostly subsistence-oriented farming context the zaï practice proved to reverse severe land degradation and improve households’ livelihood and food security.

Evaluation of effects of agri-environmental measures on rangeland degradation in two less favoured areas in Portugal
Jones, N.M. - \ 2015
University. Promotor(en): Leo Stroosnijder, co-promotor(en): Jan de Graaff; Luuk Fleskens. - Wageningen : Wageningen University - ISBN 9789462574618 - 154
agrarisch natuurbeheer - extensieve weiden - landdegradatie - milieuafbraak - landgebruik - bedrijfssystemen - portugal - agri-environment schemes - rangelands - land degradation - environmental degradation - land use - farming systems

Evaluation of effects of agri-environmental measures on rangeland degradation in two less-favoured areas in Portugal

Nadia Manuela Jones

In the past decades there have been significant land use changes in Portugal. After the integration of Portugal in the EU, farmers have been able to benefit from EU policy measures, which were initially mainly aimed at supporting farmer’s income. It soon became apparent that these land use changes led to both intensification and abandonment of land, which were detrimental to the environment in various ways, in particular to higher soil erosion hazards and to an increased incidence of wildfire.

The thesis assesses the impact of agro-environmental policies on agro-ecosystem goods and services and land degradation at farm and regional levels in Portugal. It identifies the main land use changes, provides insight in the role of past policy measures targeting the preservation of extensive grazing in marginal areas, and explores the options for the improvement of future policy measures.

First an historical review is provided of land use changes in Portugal and their implications for land degradation and conservation. Thereafter an analysis is made of the farming systems in two less favoured areas in Centro and Alentejo regions, which showed an increasing focus on livestock and rangeland activities. Subsequently an assessment is made of the role of two specific EU agri-environmental measures (AEM) that preserve extensive grazing in these two less-favoured areas in Portugal. Thereby attention is paid to the uptake of these AEMs and to their effects on preserving reduced stocking rates and sufficient soil cover. An analysis is also made of the AEM payments and other EU subsidy flows, and their changes over the period 2005-2009, and of the effectiveness of the financial incentives offered through the two specific AEMS for preserving extensive grazing in the two research areas. Finally a normative analysis is made, whereby the impact of agri-environmental policy is targeted. Through scenario analysis of different combinations of policy measures for the two research areas, the impacts on extensive livestock farm production, soil erosion risk and wildfire hazard are assessed. A final discussion about the respective research results is presented in the synthesis of the thesis.

Evaluating temporal consistency of long-term global NDVI datasets for trend analysis
Tian, F. ; Fensholt, R. ; Verbesselt, J. ; Grogan, K. ; Horion, S. ; Wang, Y. - \ 2015
Remote Sensing of Environment 163 (2015). - ISSN 0034-4257 - p. 326 - 340.
high-resolution radiometer - structural-change models - near-infrared channels - time-series analysis - interannual variability - vegetation trends - satellite data - atmospheric correction - sensor degradation - land degradation
As a way to understand vegetation changes, trend analysis on NDVI (normalized difference vegetation index) time series data have been widely performed at regional to global scales. However, most long-term NDVI datasets are based upon multiple sensor systems and unsuccessful corrections related to sensor shifts potentially introduce substantial uncertainties and artifacts in the analysis of trends. The temporal consistency of NDVI datasets should therefore be evaluated before performing trend analysis to obtain reliable results. In this study we analyze the temporal consistency of multi-sensor NDVI time series by analyzing the co-occurrence between breaks in the NDVI time series and sensor shifts from GIMMS3g (Global Inventory Modeling and Mapping Studies 3rd generation), VIP3 (Vegetation Index and Phenology version 3), LTDR4 (Long Term Data Record version 4) and SPOT-VGT (Système Pour l'Observation de la Terre VEGETATION). Single sensor time series from MODIS (MODerate Resolution Imaging Spectroradiometer) Terra and Aqua are used as reference datasets. The global land surface is divided into six regions according to the world humidity zones and averaged NDVI time series in each region are analyzed separately using a multiple structural change detection approach. We find that artifacts exist in the VIP3 and LTDR4 NDVI datasets with an abrupt shift detected in all humidity zones coinciding with the shift from NOAA-9 to NOAA-11 in 1988 and that orbital drift effects are evident in arid regions, potentially introducing uncertainties in NDVI trend analysis. Platform/sensor change from VGT-1 to VGT-2 is found to cause a significant positive break in the SPOT-VGT NDVI time series. Potential artifacts exist in humid, dry-subhumid, semi-arid and hyper-arid regions of GIMMS3g NDVI, whereas no signs of artifacts are found in the arid region. Although temporal consistency throughout all examined datasets increases after 2000 due to the usage of advanced platforms and sensors, variations in NDVI values from 2010 to 2011 still result in different trends at global and regional scales.
Challenging conservation agriculture on marginal slopes in Sehoul, Morocco
Schwilch, G. ; Laouina, A. ; Chaker, M. ; Machouri, N. ; Sfa, M. ; Stroosnijder, L. - \ 2015
Renewable Agriculture and Food Systems 30 (2015)3. - ISSN 1742-1705 - p. 233 - 251.
land degradation - rainwater use - management - soil - efficiency - adoption - africa
In Sehoul, Morocco, the use of marginal land for agriculture became a necessity for the local population due to increased poverty and the occupation of the best land by new owners. Desertification poses an additional threat to agricultural production on marginal slopes, which are often stony and degraded. In a participatory process embedded in the EU DESIRE research project, potential sustainable land management measures were selected to address land degradation and desertification. Promising experiences with no-tillage practices elsewhere in Morocco had motivated the Moroccan government to promote conservation agriculture throughout the country. This combination of crop rotation, minimal soil disturbance and soil cover maintenance, however, had not yet been tested on sloping degraded land. Field trials of grazing enclosure combined with no or minimum tillage were conducted on the plots of two farmers, and trial results were analyzed based on stakeholders’ criteria. Results suggest that increased soil cover with barley residues improved rainwater use efficiency and yields only slightly, although soil water was generally enhanced. Soil moisture measurements revealed that no-tillage was favorable mainly at soil depths of 5cm and in connection with low-rainfall events (<20mm); under these circumstances, moisture content was generally higher under no-tillage than under conventional tillage. Moreover, stakeholder discussion confirmed that farmers in Sehoul remain primarily interested in animal husbandry and are reluctant to change the current grazing system. Implementation of conservation agriculture is thus challenged both by the degraded, sloping and stony nature of the land, and by the socio-economic circumstances in Sehoul.
Agriculture Beyond Food: Experiences from Indonesia
Loffler, H.J.M. ; Afiff, S. ; Burgers, P.P.M. ; Govers, C. ; Heeres, H.J. ; Karyanto, O. ; Manurung, R. ; Vel, J.A.C. ; Visscher, S. ; Zwaagstra, T. ; Widyarani, R. - \ 2014
The Hague : NWO/WOTRO - ISBN 9789077875858 - 117
oliepalmen - biobrandstoffen - biobased economy - biodiesel - reststromen - landdegradatie - jatropha - economische ontwikkeling - projecten - indonesië - oil palms - biofuels - residual streams - land degradation - economic development - projects - indonesia
The ABF programme addresses one of today’s major societal challenges, how to achieve a sustainable and inclusive biobased economy, with high-level scientific research on the thin lines between food and non-food, commodities and waste products, livelihood opportunities and risks, and local and global economy. This book provides insights into the main issues and key questions relating to the biobased economy, reflects on the objectives of the ABF programme, and offers policy recommendations. It summarises the projects conducted within the three major clusters at the heart of the programme: migration and forest transformation, breakthroughs in biofuel production technology, and the commoditisation of an alternative biofuel crop. The book ends with a number of lessons learned from the ABF programme on interdisciplinary programming.
Agroforestry solutions to address climate change and food security challenges in Africa
Mbow, C. ; Neufeldt, H. ; Noordwijk, M. van; Minang, P.A. ; Kowero, G. ; Luedeling, E. - \ 2014
Current Opinion in Environmental Sustainability 6 (2014). - ISSN 1877-3435 - p. 61 - 67.
sub-saharan africa - forest degradation - land degradation - climate-change - west-africa - agriculture - systems - intensification - classification - security
Trees inside and outside forests contribute to food security in Africa in the face of climate variability and change. They also provide environmental and social benefits as part of farming livelihoods. Varied ecological and socio-economic conditions have given rise to specific forms of agroforestry in different parts of Africa. Policies that institutionally segregate forest from agriculture miss opportunities for synergy at landscape scale. More explicit inclusion of agroforestry and the integration of agriculture and forestry agendas in global initiatives on climate change adaptation and mitigation can increase their effectiveness. We identify research gaps and overarching research questions for the contributions in this special issue that may help shape current opinion in environmental sustainability.
Land management in the north-western highlands of Ethiopia: adoption and impact
Akalu Teshome Firew, ; Firew, A.T. - \ 2014
University. Promotor(en): Leo Stroosnijder, co-promotor(en): Jan de Graaff. - Wageningen : Wageningen University - ISBN 9789462571563 - 148
grondbeheer - landdegradatie - hooglanden - waterbescherming - bodembescherming - ethiopië - land management - land degradation - highlands - water conservation - soil conservation - ethiopia


Over the last four decades, the government of Ethiopia and various a consortium of donors have been promoting different land management (LM) practices in the highlands of Ethiopia to halt land degradation. However, the adoption rate of these practices has been low. This is because investments in LM practices are influenced by various institutional, socio-economic and bio-physical factors. The main objective of this research is to investigate the impact of these different factors on investments in LM in the north-western Ethiopian highlands. It focuses on the drivers of the different stages of adoption, on profitability of LM practices, and on land quality, land fragmentation, tenure arrangements and social capital.

We examined the drivers of the different stages of adoption of soil and water conservation (SWC) practices using an ordered probit model. The results indicate that adoption of soil and water conservation (SWC) passes through four major phases: non-adoption/dis-adoption, initial adoption, actual adoption and final adoption. Some socio-economic and institutional factors have a different effect on the respective SWC adoption phases. Final adoption depends mostly on profitability, land-related factors, social capital and perception of erosion problems.

We also investigated the effectiveness and profitability of three SWC practices (stone bunds, soil bunds and Fanya juu bunds) using the Universal Soil Loss Equation (USLE) and Cost Benefit Analysis (CBA). The results show that SWC practices are effective in controlling soil erosion, though the profitability of these SWC methods is dependent on the site where they are used. Fanya juu and stone bunds are generally profitable under standard conditions (e.g. medium slope and average soil quality and labour costs). However, the study also shows that different underlying assumptions change the CBA results considerably and consequently also change the conclusions regarding circumstances under which SWC measures are or are not profitable.

Besides, we assessed farmers’ perceptions about land quality, land fragmentation and tenure systems and their influence on interrelated LM (Bunds, Compost/Manure and Fertilizer) investments using a multivariate probit (MPV) model. The study shows that investments in LM practices are interdependent. For example, compost/manure and fertiliser substitute each other to a certain extent (often not used together, or used interchangeably by farmers) in the farming system of the study areas. Land quality (e.g. slope and soil fertility status), land fragmentation (parcel size and distance of parcel from homestead) and tenure arrangements influence farmers’ investments in LM practices.

In addition, the relationship between the different dimensions of social capital and investments in LM practices was explored. The results show that the different dimensions of social capital affect LM practices differently. In particular, the cooperation and trust dimensions of social capital are associated with the intensity of investment in SWC bunds and fertiliser use. The extent of participation in formal institutions has a positive effect on the use of fertiliser and compost.

Furthermore, we evaluated different SWC practices using Multi-Criteria Analysis (MCA) to assess their ecological, economic and social impacts. The study reveals that MCA is an effective evaluation tool that can take into account non- monetary and less quantifiable effects of SWC measures, which is not possible with Cost Benefit Analysis. The results of the analysis indicate that farmers have a range of criteria to evaluate the performance of SWC measures. The relative importance of each criterion in the selection of SWC alternatives depends to a large extent on slope categories.

For enhancing the adoption and impacts of land management, there is a need to increase knowledge about location specific viable LM practices, to promote collective action at watershed level, to pay more attention to farmers’ preferences and to improve the capacity and capability of farmers.

Effects of soil bunds on runoff, soil and nutrient losses, and crop yield in the Central Highlands of Ethiopia
Adimassu Teferi, Z. ; Mekonnen, K. ; Yirga, C. ; Kessler, A. - \ 2014
Land Degradation and Development 25 (2014)6. - ISSN 1085-3278 - p. 554 - 564.
water conservation - northern ethiopia - land degradation - smallholders - management - rainfall - tigray - technologies - investments - variability
The effects of soil bunds on runoff, losses of soil and nutrients, and crop yield are rarely documented in the Central Highlands of Ethiopia. A field experiment was set up consisting of three treatments: (i) barley-cultivated land protected with graded soil bunds (Sb); (ii) fallow land (F); and (iii) barley-cultivated land without soil bund (Bc). For 3¿years (2007–2009), the effect of soil bunds on runoff, losses of soil and nutrients, and crop productivity was studied. Daily runoff and soil and nutrient losses were measured for each treatment using standard procedures while barley yield was recorded from the cultivated plots. The results showed that Sb brought about significant reduction in runoff and soil losses. Plots with Sb reduced the average annual runoff by 28¿per cent and the average annual soil loss by 47¿per cent. Consequently, Sb reduced losses of soil nutrients and organic carbon. However, the absolute losses were still high. This implies the need for supplementing Sb with biological and agronomic land management measures to further control soil erosion. Despite these positive impacts on soil quality, Sb do not increase crop yield. Calculated on a per-hectare basis, Sb even reduce crop yield by about 7¿per cent as compared with control plots, which is entirely explained by the reduction of the cultivable area by 8·6¿per cent due to the soil bunds. Suitable measures are needed to compensate the yield losses caused by the construction of soil bunds, which would convince farmers to construct these land management measures that have long-term beneficial effects on erosion control.
Zaaien op dorre bodem : wereldwijde aanpak van verwoestijning
Lynden, Godert van - \ 2013
land degradation - rehabilitation - soil degradation - soil conservation - world - desertification
Exploring the potential of co-investments in land management in the Central Rift Valley of Ethiopia
Adimassu Teferi, Z. - \ 2013
University. Promotor(en): Leo Stroosnijder, co-promotor(en): Aad Kessler. - S.l. : s.n. - ISBN 9789461734518 - 120
grondbeheer - landdegradatie - duurzaamheid (sustainability) - boeren - gewasproductie - perceptie - bodemvruchtbaarheid - watererosie - stakeholders - ethiopië - land management - land degradation - sustainability - farmers - crop production - perception - soil fertility - water erosion - ethiopia

Like in any other part of the country, land degradation resulting from water erosion and nutrient depletion is one of the most challenging problems for farmers in the Central Rift Valley (CRV) of Ethiopia. Nevertheless, investments in land management to reduce land degradation and increase agricultural production by smallholder farmers have been limited. In addition, public and private sector organizations have never collaborated to stimulate (investments in) land improvement. This study focuses on coinvestments, which are conceived as the collaboration of different stakeholders in land management in the form of material, labour, finance, technology, knowledge and governance. The overall aim of this study was to explore the potential of co-investments to foster land management and increase land productivity in the CRV of Ethiopia. Chapter 2 presents farmers’ perceptions of crop productivity and their strategies to cope with perceived changes in the CRV of |Ethiopia. It reveals that farmers perceive a decrease in crop productivity and food production over the last decades and that they blame a decline in rainfall for this. As a consequence, farmers apply different strategies to cope with, and adapt to perceived rainfall shortages and related expected yield losses. However, an analysis of rainfall data in the CRV shows that rainfall characteristics have not changed over the last three decades. Moreover, according to analysis of official data, crop productivity per hectare in the CRV even shows a slight increase over the last decade. Therefore, farmers’ perception of a decline in crop productivity and rainfall can be explained by i) the increased demand to grow more crops to feed the rapidly growing population, and ii) the lower moisture availability for plant growth as a consequence of more intensive farming (often on less suitable fields) and land degradation. The root causes of frequent food shortages are thus not only related to rainfall, but also to soil fertility decline, soil erosion and lack of rainwater storage in the soil. Current farmers’ strategies are, therefore, not adequate to cope with the increased food demand. There is an urgent need to invest in sustainable land management (SLM) practices that enhance local food production. Chapter 3 focuses on the farmers’ perception of land degradation (especially soil erosion and nutrient depletion) and their investments in land management. If farmers perceive land degradation as a problem, the chance that they invest in land management measures will be enhanced. Results reveal that land degradation in the form of water erosion and fertility depletion is a problem and has increased over the last decade in the CRV. Farmers are aware of it and consider it as a problem. Nevertheless, farmers’ investments to control water erosion and soil fertility depletion are very limited. Results also show that farmers’ awareness of both water erosion and soil fertility decline as a problem is not significantly associated with their investments in land management. Hence, even farmers who perceive land degradation on their fields and are concerned about its increase over the last decade, do not significantly invest more in water erosion and soil fertility control measures than farmers who do not perceive these phenomena. Chapter 4 is devoted to exploring the determents of farmers’ decisions how much and where to invest in land management. The study identified five major factors that influence farmers’ decisions how much to invest in land management. These include households’ resource endowments, farming experience and knowledge, access to information, social capital and availability of family labour. This result implies that extension strategies aiming at sustainable land management should try to enhance households’ resources endowments, improve their access to information and stimulate collective action in land management. Similarly, the study revealed the decisions of farmers’ where to invest in land management is influenced by the vulnerability, accessibility and fertility condition of their plots. Farmers were more willing to invest in plots that are vulnerable to water erosion, have better soil fertility and are larger. However, the influence of all these factors on farmers’ investments in land management was highly variable across the different study sites within the CRV. Hence, the diversity in social, economic, cultural and biophysical conditions must be taken into account by rural extension programmes. This calls for site-specific land management strategies that can be planned and implemented at micro-level with active participation of farmers. Chapter 5 deals with co-investments in land management. Lack of collaboration is a growing concern for the success of SLM in Ethiopia. In Ethiopia, not only farmers but also public institutions and private sectors are hesitant to collaborate and invest in SLM. This study identified several major bottlenecks and requirements for co-investments by public institutions and private sectors. Nevertheless, the results varied across the administrative levels. As a result, macro level institutions did not acknowledge most of the bottlenecks and requirements reported by meso and micro level institutions. Therefore, a micro-mesomacro consensus is required to improve co-investments. Furthermore, most bottlenecks and requirements for public institutions were related to governance issues. This suggests the need to establish good governance at all levels in Ethiopia in order to improve co-investments in SLM. In addition to public institutions, private sectors identified major bottlenecks and requirements which are mostly related to economic issues. However, given the current socio-economic and political situation in Ethiopia, it is a long way to fulfilling the requirements proposed by public institutions and private sectors. This indicates that requirements should be fulfilled gradually and systematically for successful co-investments in SLM. Chapter 6 explores the potential of co-investments in land management for bringing change at the grassroot level in Ethiopia. First, this study explores the most important co-investment activities that trigger farmers to invest in land management based on a co-investment initiative in the Galessa watershed. Second, it assesses the impact of these co-investment activities on farmers’ investments in land management by comparing experimental (participant) and control (non-participant) groups of farmers using survey data. The case study revealed that the most important co-investment activities that triggered farmers to invest in land management include co-investments in awareness creation, water provision, technology and governance. Of these activities, co-investing in water provision is the most successful activity, because it directly solves one of the basic needs of farmers in the watershed. Results reveal that the experimental group of farmers invested more in land management practices, such as soil bunds, compost and tree planting, than the control group of farmers. The article concludes that multiple level coinvestment activities are crucial to trigger farmers to invest in land management in Ethiopia. Chapter 7 is a synthesis of previous chapters. It briefly summarizes answers to the research questions, describes the added value of the thesis in terms of knowledge generation and provides suggestions for further research and policy making. The synthesis indicates that although farmers are well aware of the land degradation problem, their investments in land management are not sufficient to reverse the situation. It also reveals that farmers’ investments are affected by highly diverse socio-economic and biophysical constraints. Moreover, public and private sectors are constrained by financial and governance factors and require several preconditions before actually investing in land management. Despite these constraints at micro, meso and macro institutional levels, this thesis shows that there is potential for coinvestments in SLM in Ethiopia. Exploiting this potential principally requires commitment of all stakeholders to co-invest in land management.

Financial viability of soil and water conservation technologies in northwestern Ethiopian highlands
Teshome, Akalu ; Rolker, D. ; Graaff, J. de - \ 2013
Applied Geography 37 (2013). - ISSN 0143-6228 - p. 139 - 149.
cost-benefit-analysis - land degradation - bench terraces - adoption - pressure - erosion
Soil erosion by water is a major threat to food security, environmental sustainability and prospects for rural development in Ethiopia. Successive governments have promoted various soil and water conservation (SWC) measures in order to reduce the effects of land degradation, but adoption rates vary considerably. The profitability of SWC measures is an essential condition for their adoption. The objective of this research was to determine the economic efficiency of three different types of SWC technologies (soil bunds, stone bunds and fanya juu) in the watersheds of Debre Mewi and Anjeni in the northwestern Ethiopian highlands. A farm household survey was carried out among 60 farmers in both watersheds and the Universal Soil Loss Equation (USLE) was used to assess erosion risk on farmers' fields. A cost-benefit analysis (CBA) was then carried out to determine the profitability of the measures under different conditions. Erosion estimates for the fields suggest that adapted SWC structures were successful in reducing soil erosion. The cost-benefit analysis indicates that all SWC measures are profitable under ‘standard’ conditions, except soil bunds in Anjeni without grass cover. However, the study shows that different underlying assumptions change the CBA results considerably and consequently also change the conclusions regarding circumstances under which SWC measures are or are not profitable. This illustrates the volatility of the profitability of SWC measures.
Assessing the impact of soil degradation on food production
Bindraban, P.S. ; Velde, M. van der; Ye, L. ; Berg, M. van den; Materechera, S. ; Kiba, D.I. ; Tamene, L. ; Ragnarsdottir, K.V. ; Jongschaap, R.E.E. ; Hoogmoed, M. ; Hoogmoed, W.B. ; Beek, C.L. ; Lynden, G.W.J. van - \ 2012
Current Opinion in Environmental Sustainability 4 (2012)5. - ISSN 1877-3435 - p. 478 - 488.
conservation agriculture - carbon sequestration - land degradation - africa - erosion - yield - management - security - climate - trends
Continuing soil degradation remains a serious threat to future food security. Yet, global soil degradation assessments are based on qualitative expert judgments or remotely sensed quantitative proxy values that suffice to raise awareness but are too coarse to identify appropriate sustainable land management interventions. Studies in China and Sub Saharan Africa illustrate the considerable impact of degradation on crop production but also point to the need for solutions dependent on location specific agro-ecological conditions and farming systems.The development of a comprehensive approach should be feasible to better assess both extent and impact of soil degradation interlinking various scales, based on production ecological approaches and remote sensing to allow disentangling natural and human induced causes of degradation. A shared common knowledge base cataloguing hard-won location-specific interventions is needed for successfully preventing or mitigating degradation
Effect of vegetation cover and transitions on regional wind erosion in drylands
Youssef, I.F. - \ 2012
University. Promotor(en): Leo Stroosnijder, co-promotor(en): Saskia Visser; D. Karssenberg. - S.l. : s.n. - ISBN 9789461733429 - 132
vegetatie - winderosie - landdegradatie - modelleren - modellen - meting - droge gebieden - vegetation - wind erosion - land degradation - modeling - models - measurement - arid lands

Wind erosion is a critical environmental problem that threatens mainly the arid and semi-arid regions of our planet. Usually this problem is associated with desertification, poverty and other environmental and socioeconomic problems. Wind erosion causes the loss of fertile topsoil, and has a negative effect on agricultural production and on human health. When conditions favorable for wind erosion are present, the process can cause large scale environmental disasters like the Dust Bowl in the USA in the 1930s. This event is considered one of the worst environmental disasters of the 20th century, and was caused by a reduction in vegetation cover due to a change in land use combined with an increased dryness in the region. Wind erosion involves the detachment, transport and deposition of soil particles. Depending on their size, particles can move in three different types of transport: creep, saltation and suspension. Vegetation is one of the key factors in the protection of the soil against erosive winds. Although research on wind erosion has started a few decades ago there is still a big gap between the available knowledge provided by current measurement and modeling tools and the knowledge which is required by policy makers and land managers. This thesis focuses on improving the knowledge of the effects of vegetation cover and land use on regional scale wind erosion. The thesis covers improvement of wind erosion measurement techniques (Chapters 2, 3 and 5) and wind erosion modeling on the regional scale

(Chapter 4 and 6).

In Chapter 2, the efficiencies of the Vaseline Slide (VS) and Modified Wilson and Cooke (MWAC) catchers were determined with different sand particle sizes (<50, <75, 50–75, 200–400, and 400– 500 μm) at a fixed wind speed (13.3 m s–1) and with different soil textures at different wind velocities (10.3, 12.3, and 14.3 m s–1). The study showed that whereas the VS trap is better for catching fine particles, the MWAC trap is better for trapping coarse particles. In the experiments with different soil textures, the efficiency of each catcher considerably changed with the with wind speed. This also varies importantly between catchers: for instance, for sand the MWAC efficiency was relatively high, whereas the efficiency of VS catcher was relatively low. Results concluded that the efficiency of each catcher varies critically with particle size, soil texture and wind speed. Equipment or measurement techniques for the observation of saltation at the regional scale does not exist although these are essential for improving the understanding of wind erosion problem at that scale. In Chapter 3, the portable plot method for measuring regional scale wind erosion with a specific focus on the saltation process was developed. With this strategy the number of measurement locations is increased with limited budget and time. The portable plot method was applied at agricultural stability zones 4 and 5 in the Khanasser Valley in Syria in 2009 and 2010. During the measurement period, a meteorological station was installed at each plot together with MWAC sediment catchers. Results showed that, with this method, information on the effect of wind regime on the aeolian mass transport for different land uses in the region can be obtained. Also, insights into the interrelation between neighboring land units can be gained and the data for scaling-up a field scale model to the regional scale are obtainable. We concluded that this method provides insight into the wind erosion at regional scale and data collected through it are important for progressing the modeling of wind erosion at a regional scale. The new measurement method enabled the calibration and validation of the field scale model of RWEQ (Revised Wind Erosion Equation) at several land use areas in the Khanasser valley in Syria (Chapter 4). In this chapter, the RWEQ model was modified to estimate mass flux and soil loss at a field scale for different types of land use. We implemented this modified version of RWEQ that represents wind erosion as a transient process, using time steps of 6 hours. Beside this, a number of adaptations including the estimation of mass flux over the field boundaries and the routing of sediment have been added. The results showed that this modified version of RWEQ provided acceptable predictions for the average mass flux from our measurement plots compared with the results of previous tests of the model. While the portable plot method provided insights on the effect of land use and climate on the quantity and intensity of wind erosion in a region, more knowledge was required on the border effect between different land uses as the portable plot method provided only limited knowledge on the effect of vegetation pattern and border effect. To get sufficient knowledge on this subject a simulation of sediment transport in a regional scale environment was designed and tested in wind-tunnel experiments (Chapter 5). This simulation showed the effect of vegetation pattern on sediment transport within a land unit and at the border between land units. Wind tunnel experiments were conducted with artificial shrubs representing Atriplex halimus, a native shrub in Khanassar valley. In the experiments, a wind speed of 11 m s-1 was applied and after each 200-230 second wind run the sediment redistribution was measured using a graph paper. Results showed that: 1) the transport within a land unit is affected by the vegetation density and pattern for the land unit itself and for the neighboring units; 2) plans for re-vegetation of degraded land need to take into account the ‘streets’ effect; 3) the effect of neighboring land units includes a sheltering effect and the regulation of sediment passing from one land unit to the neighboring land units and 4) revegetation projects in regions vulnerable to wind erosion not only need to investigate the effect of vegetation pattern on erosion and deposition within the region in general, but also should consider the redistribution of sediment at smaller scales. In Chapter 6, The Regional Scale Wind Erosion Equation (RS-WEQ) was developed. This model takes the different land uses in a region into account, considers the interrelation between neighboring land units and considers saltation as the main transport mode. Although the RWEQ was the starting point for the development of RS-WEQ, the new model is not restricted in its application to a single field. RS-WEQ predicts mass flux, soil loss and deposition for all land uses in a region. The model considers the erodibility parameters for each land use independently and takes the effect of the borders into account. Its output provides a clear insight on wind erosion processes at the regional scale. RS-WEQ was run using scenarios that represent main land uses in dry regions in general and in Khanasser valley specifically. The model outputs showed that the wind speed, field length and land use patterns affect the quantity and severity of mass flux, soil loss and deposition in a region. Specifically, the results showed that the mean mass flux and its related abrasion risk increased with the increase in wind speed and field length. The model provides further details on the effect of field length and land use patterns on the severity of soil loss and deposition at the regional scale. Therefore the developed model can be considered as a useful tool for land managers and policy makers in regions that are vulnerable to wind erosion. This thesis showed that for comprehensive understanding of the aeolian sediment transport at regional scale a combination of measuring and modeling of wind-blown sediment transport is required. And the intensively calibrated and validated wind erosion models can be used in the framework of wind erosion mitigation.

Analysis of vegetation-activity trends in a global land degradation framework
Jong, R. de - \ 2012
University. Promotor(en): Michael Schaepman, co-promotor(en): Sytze de Bruin. - S.l. : s.n. - ISBN 9789461733122 - 147
vegetatie - vegetatie-indexen - landdegradatie - cartografie - monitoring - observatie - exploratie - klimaat - seizoenvariatie - satellietbeelden - remote sensing - vegetation - vegetation indices - land degradation - mapping - observation - exploration - climate - seasonal variation - satellite imagery

Land degradation is a global issue on a par with climate change and loss of biodiversity, but its extent and severity are only roughly known and there is little detail on the immediate processes – let alone the drivers. Earth-observation methods enable monitoring of land resources in a consistent, physical way and on global scale by making use of vegetation activity and/or cover as proxies. A well-known spectral proxy is the normalized difference vegetation index (NDVI), which is available in high temporal resolution time series since the early 1980s. In this work, harmonic analyses and non-parametric trend tests were applied to the GIMMS NDVI dataset (1981–2008) in order to quantify positive changes (or greening) and negative changes (browning). Phenological shifts and variations in length of growing season were accounted for using analysis by vegetation development stage rather than by calendar day. This approach does not rely on temporal aggregation for elimination of seasonal variation. The latter might introduce artificial trends as demonstrated in the chapter on the modifiable temporal unit problem. Still, a major assumption underlying the analysis is that trends were invariant, i.e. linear or monotonic, over time. However, these monotonic trends in vegetation activity may consist of an alternating sequence of greening and/or browning periods. This effect and the contribution of short-term trends to longer-term change was analysed using a procedure for detection of trend breaks. Both abrupt and gradual changes were found in large parts of the world, especially in (semi-arid) shrubland and grassland. Many abrupt changes were found around large-scale natural influences like the Mt Pinatubo eruption in 1991 and the strong 1997/98 El Niño event. This marks the importance of accounting for trend changes in the analysis of long-term NDVI time series. These new change-detection techniques advance our understanding of vegetation variability at a multi-decadal scale, but do not provide links to driving processes. It is very complex to disentangle all natural and human drivers and their interactions. As a first step, the spatial relation between changes in climate parameters and changes in vegetation activity was addressed in this work. It appeared that a substantial proportion (54%) of the spatial variation in NDVI changes could be associated to climatic changes in temperature, precipitation and incident radiation, especially in forest biomes. In other regions, the lack of such associations might be interpreted as human-induced land degradation. With these steps we demonstrated the value of global satellite records for monitoring land resources, although many steps are still to be taken.

Myths in Land Degeradation and Development
Stroosnijder, L. - \ 2012
Wageningen : S.n. - 20
landdegradatie - meting - landverbetering - land degradation - measurement - land improvement
Water erosion is the most important degradation process of the 10 degradation processes distinguished by the European Union. The impact of rain drops on the soil surface causes splash of soil particles
Competing claims and food security in Ghana and Mali
Berkum, S. van; Dijk, M. van; Bodegom, A.J. van; Jongschaap, R.E.E. ; Arets, E.J.M.M. ; Bindraban, P.S. - \ 2012
The Hague : LEI, part of Wageningen UR (Report / LEI Wageningen UR : Research area International policy ) - ISBN 9789086155606 - 77
voedselzekerheid - voedselproductie - landbouw en milieu - productiviteit - ecosystemen - bosgebieden - wetlands - savannen - landdegradatie - food security - food production - agriculture and environment - productivity - ecosystems - woodlands - savannas - land degradation
Linear trends in seasonal vegetation time series and the modifiable temporal unit problem
Jong, R. de; Bruin, S. de - \ 2012
Biogeosciences 9 (2012). - ISSN 1726-4170 - p. 71 - 77.
proxy global assessment - land degradation - sahel - environment - america - modis - ndvi
Time series of vegetation indices (VI) derived from satellite imagery provide a consistent monitoring system for terrestrial plant productivity. They enable detection and quantification of gradual changes within the time frame covered, which are of crucial importance in global change studies, for example. However, VI time series typically contain a strong seasonal signal which complicates change detection. Commonly, trends are quantified using linear regression methods, while the effect of serial autocorrelation is remediated by temporal aggregation over bins having a fixed width. Aggregating the data in this way produces temporal units which are modifiable. Analogous to the well-known Modifiable Area Unit Problem (MAUP), the way in which these temporal units are defined may influence the fitted model parameters and therefore the amount of change detected. This paper illustrates the effect of this Modifiable Temporal Unit Problem (MTUP) on a synthetic data set and a real VI data set. Large variation in detected changes was found for aggregation over bins that mismatched full lengths of vegetative cycles, which demonstrates that aperiodicity in the data may influence model results. Using 26 yr of VI data and aggregation over full-length periods, deviations in VI gains of less than 1% were found for annual periods (with respect to seasonally adjusted data), while deviations increased up to 24% for aggregation windows of 5 yr. This demonstrates that temporal aggregation needs to be carried out with care in order to avoid spurious model results.
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