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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.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    A process for effective desertification mitigation
    Schwilch, G. - \ 2012
    Wageningen University. Promotor(en): Leo Stroosnijder; H. Hurni, co-promotor(en): Jan de Graaff. - S.l. : s.n. - ISBN 9789461732880 - 178
    woestijnvorming - grondbeheer - duurzaamheid (sustainability) - besluitvorming - participatie - stakeholders - bodembescherming - milieueffect - mitigatie - desertification - land management - sustainability - decision making - participation - stakeholders - soil conservation - environmental impact - mitigation

    in these ecosystems can easily result in widespread and severe land degradation and thus desertification.
    Combined with global issues such as climate change, economic disparities, migration, and competing claims
    on land, this often leads to a vicious cycle of aridity, land degradation, and productivity loss. In addition to
    the harsh environmental conditions limiting land productivity, the socio-economic situation in drylands can
    pose challenges as well, given that these regions are often characterised by remoteness, marginality, lowproductivity
    farming, weak institutions, and even conflict. Managing land sustainably under such conditions
    is a challenge which concerns land users and other stakeholders, policymakers, and researchers alike.
    Desertification research has traditionally focused on degradation assessments, whereas prevention and
    mitigation strategies have not sufficiently been emphasised, although the concept of sustainable land
    management (SLM) is increasingly being acknowledged (Chapter 1).
    The present research was embedded in the EU FP6 research project DESIRE (Desertification
    Mitigation and Remediation of Land – a Global Approach for Local Solutions; 2007–2012). DESIRE aimed to
    establish promising alternative land use and management strategies in 17 areas affected by land
    degradation and desertification around the world. Project work was based on close collaboration of
    scientists with local stakeholder groups. The study sites served as a global laboratory for developing and
    applying new methods of science – stakeholder collaboration and trialling traditional and innovative
    approaches to combating desertification.
    Chapter 2 offers a compilation and review of a number of methodological approaches to monitoring
    and assessing SLM which to date have been little reported in the literature. Lessons are drawn from these
    experiences, and common elements and future pathways are identified as a basis for a global approach.
    The local-level methods of the World Overview of Conservation Approaches and Technologies (WOCAT)
    framework serve to catalogue SLM technologies and approaches as case studies. This tool was included in
    the local-level Land Degradation Assessment in Drylands (LADA) as well as in the DESIRE project.
    Complementary site-based approaches can enhance an ecological process-based understanding of SLM
    variation. At national and sub-national levels, a joint WOCAT/LADA/DESIRE spatial assessment based on
    land use systems can be used to identify the status and trends of degradation and SLM, including causes,
    drivers, and impacts on ecosystem services. Expert consultation is combined with scientific evidence and,
    where necessary, enhanced with secondary data and indicator databases. Key lessons learnt include the
    need for a multi-scale approach, for using common indicators, and for drawing on a variety of information
    sources, including scientific data and local knowledge, by means of participatory methods. Methodological
    consistency allows for cross-scale analyses, and findings can be analysed and documented for use by
    decision-makers at various levels. Effective monitoring and assessment of SLM (e.g. for the United Nations
    Convention to Combat Desertification, UNCCD) requires a comprehensive methodological framework
    agreed upon and adopted by the major players.
    Although a variety of conservation measures are already applied at the local level, they are not
    adequately recognised, evaluated, and shared by land users, technicians, researchers, and policymakers.
    Likewise, collaboration between researchers and implementers is often insufficient. Chapter 3 presents a
    new methodological framework for a participatory process of appraising and selecting desertification
    mitigation strategies, and outlines first experiences from its application in the DESIRE project. The
    methodology – a key product developed within this PhD study – combines a collective learning and
    decision-making approach with the use of evaluated global best practices. It moves through a concise
    process in three parts, starting out with the identification of land degradation and locally applied solutions
    in a stakeholder workshop, followed by an assessment of local solutions using a standardised evaluation
    tool, and ending with the joint selection of promising strategies for implementation with the help of a
    decision support tool. A preliminary analysis of the application of the first part of the methodology showed
    that the initial stakeholder workshop resulted in a good basis for stakeholder cooperation and yielded
    promising land conservation practices for further assessment. Study site research teams appreciated the
    results, which they considered particularly valuable because urgent issues and promising options had
    emerged from joint reflection. The methodology was found to be suitable for initiating mutual learning
    among different stakeholder groups, as well as for integrating local and scientific knowledge.
    The thus identified SLM practices were then documented and evaluated by local researchers in
    collaboration with land users and using the internationally recognised and standardised WOCAT
    questionnaires. These in-depth assessments of 30 technologies and 8 approaches are analysed and
    compared across the DESIRE study sites in Chapter 4, highlighting key issues of SLM in drylands. Careful
    attention is paid to features which specifically characterise SLM in drylands and make SLM practices
    especially useful regarding the identified threats. Among the achievements attributed to the documented
    technologies, those mentioned most were diversified and enhanced production, as well as better
    management of water and soil degradation, whether by means of water harvesting, by improving soil
    moisture, or by reducing runoff. Demonstrating a favourable local-scale cost–benefit relationship was
    found to be crucial to improving people’s livelihoods and preventing further outmigration. However, it was
    also found that more research is needed to support the case study authors’ assessments of SLM impacts as
    well as to provide a solid rationale for investments in SLM.
    There are many and often competing options for SLM, and each must be assessed – and sometimes
    negotiated – prior to implementation. This makes SLM a classic multi-stakeholder issue which concerns
    individual and community land users, agricultural advisors, natural resource managers, government
    authorities, civil society, and researchers alike. Selecting appropriate SLM technologies for implementation
    thus requires an approach that is capable of integrating the diverse knowledge, perceptions, and
    judgements of the different stakeholders involved. Time and resource constraints often impede the
    development of contextualised, targeted, and sophisticated decision support systems. The DESIRE research
    project provided an excellent opportunity to develop and test a generic decision support methodology,
    using it to assist the study site teams in selecting, together with stakeholders in a stakeholder workshop,
    the most promising SLM option(s) for subsequent test implementation in the field (Chapter 5). Special
    attention was paid to the screening of local innovations, the selection and adaptation of potential SLM
    technologies, and the decision-making process determining which options are to be implemented. Chapter
    5 reviews the application of the DESIRE decision support methodology in a variety of biophysical and socioeconomic
    contexts, finding it to be well-structured, comprehensive, and relatively easy to apply. The builtin
    global database of SLM options provided knowledge from various environments, while the use of simple
    software allowed for easy calculation and visualisation of results. The scoring and negotiation of each
    option’s sustainability forced stakeholders to consider and acknowledge each other’s positions and
    opinions, ensuring that the final choice was well-accepted. The methodology included seeking
    commitments from stakeholders to implement the selected option(s). Challenges included the complexity
    of the issues at hand and the need for skilled moderators. Nonetheless, positive outcomes and user
    feedback confirmed that the DESIRE decision support methodology is an easy-to-use stepwise methodology
    for facilitating decision-focused participatory processes.
    Participatory and multi-stakeholder approaches are increasingly motivated by social learning and
    empowerment goals. Yet there remains a lack of practical tools for facilitating such processes. The research
    presented here aimed to close the gap between the theory and the practice of stakeholder participation
    and learning in decision-making processes concerned with SLM. Chapter 6 analyses and describes how the
    3-part participatory methodology for selecting SLM options contributed to multi-stakeholder learning.
    Cross-site analysis and in-depth evaluation of the Moroccan and Portuguese sites were used to evaluate
    how well the proposed process facilitated stakeholder learning and the selection of appropriate SLM
    options for local implementation. The structured nature of the process – starting with the joint setting of
    SLM goals – was found to facilitate mutual understanding and collaboration between stakeholders. The
    deliberation process led to a high degree of consensus over the outcome and, although this had not been
    an initial aim, in many cases also fostered social learning. This solution-oriented methodology is applicable
    in a wide range of contexts and can be implemented with limited time and resources.
    Chapter 7 presents insights into the field implementation of one of the selected SLM measures in
    Sehoul, Morocco. The Moroccan DESIRE study site was located near the city of Rabat, in an area where
    desertification poses a threat to marginal and often stony and degraded slopes. The use of marginal and
    stony land by the local population had become necessary due to increased poverty and the occupation of
    the best stretches of land by new owners. The land use change from grazing to cropping caused a
    deterioration of the field water balance, characterised by increased water loss through runoff, drainage,
    and evaporation, and resulting in less primary production. 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. The field trial results showed
    that covering the soil with crop residues neither improved yields nor increased rainwater use efficiency,
    although soil water was generally enhanced. Soil moisture measurements revealed that no-tillage was
    favourable mainly at soil depths of 5 cm and in connection with low-rainfall events (< 20 mm); under these
    circumstances, moisture content was generally higher under no-tillage than under conventional tillage.
    Moreover, farmers in Sehoul were found to be primarily interested in animal husbandry, and both crop
    residues and grains were used as feed. Chapter 7 concludes with lessons learnt from the on-farm trials in
    Sehoul.
    The synthesis (Chapter 8) offers more detailed reflection on certain key aspects of the research
    findings, such as the 3-part methodology, monitoring and assessment, stakeholder collaboration and
    learning, decision support, and desertification mitigation by means of SLM technologies and approaches.
    This is followed by a review of challenges and limitations of the proposed methodological framework and
    an assessment of its overall impact. The chapter concludes with an outlook and recommendations. One
    major conclusion is that research needs to move beyond simply idealising and promoting participatory
    approaches and learning processes: in addition, researchers must also advocate the provision of time and
    resources and the establishment of long-term partnerships by both scientific and policymaking bodies. Indepth
    and long-term field-based research remains important, but it requires sufficient resources and longterm
    commitment in order to provide adequate evidence. The methodology developed within this thesis is
    not limited to desertification; it is appropriate and useful for tackling land degradation anywhere in the
    world and for advancing towards more sustainable decisions on SLM strategies with a higher acceptance
    among stakeholders. Negotiation of, and deliberation over, ecosystem services might be the key to
    boosting SLM beyond the local scale, while at the same time compensating land users for their crucial
    efforts to combat desertification.

    Desire for greener land : options for sustainable land management in drylands
    Schwilch, G. ; Hessel, R. ; Verzandvoort, S.J.E. - \ 2012
    Bern [etc.] : University of Bern [etc.] - ISBN 9789461733290 - 282
    droge gebieden - grondbeheer - duurzaamheid (sustainability) - duurzaam bodemgebruik - woestijnvorming - bodembescherming - waterbeheer - teeltsystemen - begrazingsbeheer - bosbedrijfsvoering - arid lands - land management - sustainability - sustainable land use - desertification - soil conservation - water management - cropping systems - grazing management - forest management
    Desire for Greener Land compiles options for Sustainable Land Management (SLM) in drylands. It is a result of the integrated research project DESIRE (Desertification Mitigation and Remediation of Land - A Global Approach for Local Solutions). Lasting five years (2007–2012) and funded within the EU’s Sixth Framework Programme, DESIRE brought together the expertise of 26 international research institutes and non-governmental organisations. The DESIRE project aimed to establish promising alternative land use and management strategies in 17 degradation and desertification sites around the world, relying on close collaboration between scientists and local stakeholder groups. The study sites provided a global laboratory in which researchers could apply, test, and identify new and innovative approaches to combatting desertification. The resulting SLM strategies are local- to regional-scale interventions designed to increase productivity, preserve natural resource bases, and improve people’s livelihoods. These were documented and mapped using the internationally recognised WOCAT (World Overview of Conservation Approaches and Technologies) methodological framework, which formed an integral part of the DESIRE project. The DESIRE approach offers an integrated multidisciplinary way of working together from the beginning to the end of a project; it enables scientists, local stakeholders and policy makers to jointly find solutions to desertification. This book describes the DESIRE approach and WOCAT methodology for a range of audiences, from local agricultural advisors to scientists and policymakers. Links are provided to manuals and online materials, enabling application of the various tools and methods in similar projects. The book also includes an analysis of the current context of degradation and SLM in the study sites, in addition to analysis of the SLM technologies and approaches trialled in the DESIRE project. Thirty SLM technologies, eight SLM approaches, and several degradation and SLM maps from all the DESIRE study sites are compiled in a concise and well-illustrated format, following the style of this volume’s forerunner where the land is greener (WOCAT 2007). Finally, conclusions and policy points are presented on behalf of decision makers, the private sector, civil society, donors, and the research community. These are intended to support people’s efforts to invest wisely in the sustainable management of land – enabling greener drylands to become a reality, not just a desire.
    Exploring farmers' perceptions of drought in Tanzania and Ethiopia
    Slegers, M.F.W. - \ 2008
    Wageningen University. Promotor(en): Leo Stroosnijder, co-promotor(en): Jan de Graaff. - S.l. : S.n. - ISBN 9789085852407 - 217
    droogte - boeren - perceptie - ethiopië - tanzania - klimaatverandering - woestijnvorming - drought - farmers - perception - ethiopia - tanzania - climatic change - desertification
    Development actions focusing on land degradation in Sub-Saharan Africa have not been particularly successful in changing farmers’ agricultural practices towards a more sustainable use of natural resources. Over time, programs have become more localized and participative, which is a positive step forward. However, these programs still depart from the productivity-reducing problems that are identified and perceived by scientists. Subsistence farmers in this region believe that other problems, such as drought are bigger constraints to them. Very little is known about how subsistence farmers in semi-arid East Africa perceive drought. The aim of this research is to bridge this gap between farmers and scientists to improve the impact of interventions aimed at improving agricultural productivity. The research focuses on two study areas within Tanzania and Ethiopia, where during the period between 2004 and 2006, sociological and biophysical studies were conducted.
    Both case studies demonstrate the inter-relationship of human and natural systems. This is also part of farmers’ knowledge. Farmers’ perceptions of drought relate to the scientific concept of agricultural drought. Rainfall patterns are perceived to be negatively affected by deforestation, while soil erosion and continuous cultivation diminish soil fertility and a soil’s capacity to retain water. Farmers recognize that one has to be an active farmer to be productive and to withstand drought conditions. No one-size-fits-all solution exists for which SWC strategies to use, or for strategies to deal with climate variability and drought. Actions have to be area-specific and focused on local practices and the constraints that farmers have to deal with. Farmers’ strategies for dealing with the insecurity of the rains are multifocal. Interventions should target these multiple sectors and spheres in which people are engaged. The seemingly different problems of land degradation and drought are linked. Rather than “bridging a gap”, the issue is to find where both paths are connected. To achieve this, emphasis should lie on integrated studies and on improving the interaction between farmers and scientists.
    Geomorphology and human palaeoecology of the Méma, Mali
    Vries, E. de; Makaske, B. ; Tainter, J.A. ; McIntosh, R.J. - \ 2005
    Wageningen : Alterra (Alterra-rapport 1244) - 119
    archeologie - paleo-ecologie - mali - geomorfologie - woestijnvorming - paleoklimatologie - archaeology - palaeoecology - mali - geomorphology - desertification - palaeoclimatology
    The Méma is a semi-arid region in central-Mali with a rich archaeological heritage indicating the former existence of large urban settlements. Previous investigations suggest that the Méma is an important area in which to study the origins of Sahelian agriculture, metallurgy, and urbanism, the continuing effects of long-term desiccation, the fluvial history of the Niger River basin, human responses to desertification, and regional abandonment. As a basis for such future studies, a geomorphological map of the Méma was made based on remote sensing and field data. In this report the geomorphological map is presented with a discussion of the origin and chronology of the landforms. Following upon this discussion, the archaeology of the Méma is described, with theoretical considerations about the origin of urbanism and the abandoment of the urban settlements
    Science, technology and agency in the development of droughtprone areas: a cognitive history of drought and scarcity
    Vincent, L.F. - \ 2004
    The Open University. Promotor(en): D.V. Wield. - - 396
    droogte - aride klimaatzones - droog klimaat - woestijnvorming - waterbeheer - watervoorraden - sociaal milieu - sociale instellingen - politiek - schaarste - sociale factoren - agentschappen - bureaucratie - drought - arid zones - arid climate - desertification - water management - water resources - social environment - social institutions - politics - scarcity - social factors - agencies - bureaucracy
    Land-surface and boundary layer processes in a semi-arid heterogeneous landscape
    Jochum, A.M. - \ 2003
    Wageningen University. Promotor(en): Bert Holtslag, co-promotor(en): H.A.R. de Bruin. - Wageningen : S.n. - ISBN 9789058088246 - 155
    atmosfeer - droge gebieden - droog klimaat - woestijnvorming - wiskundige modellen - spanje - aardoppervlak - grenslaag - atmosphere - arid lands - arid climate - desertification - mathematical models - spain - land surface - boundary layer

    The European Field Experiment in a Desertification-threatened Area (EFEDA) provides a comprehensive land-surface dataset for a semiarid Mediterranean environment. It is used here to study heat and moisture transport processes in the atmospheric boundary layer (ABL), to derive grid-scale surface fluxes for numerical weather prediction models, and to evaluate the performance of the High-Resolution Limited-Area Model (HIRLAM).

    Boundary layer budgets were derived for two sub-regions of the EFEDA area with different moisture characteristics. The budget analysis is based on the synergistic combination of the observational dataset and a simple coupled canopy-mixed layer model. The mixed layer (ML) warming is balanced by a combination of the heat flux divergence and the radiative divergence (directly measured by aircraft). The large radiative warming is consistent with the high aerosol load and low visibility observed in the area. The moisture budgets reflect the influence on non-ABL scales on the entrainment moisture flux, which changes sign over time as the ABL grows into the observed heterogeneous moisture structure of the residual layer (RL). Accurate high-resolution vertical humidity profiles are needed to properly estimate the moisture flux divergence, which varies in space and time. The coupled canopy-ML slab model proves to be a valuable tool in this complex environment, if it is regularly provided with updated RL gradients. The potential for moisture flux divergence and associated ML moistening is higher at Barrax, where irrigation enhances the surface evapotranspiration.

    The area-aggregated fluxes (in particular of moisture) depend strongly on the location of the area boundaries, whenever a significant fraction of irrigated land is present. This confirms the importance to adequately account for tiles of irrigated land in surface schemes and the corresponding physiographic databases of large scale models. A simple way to accommodate a minimum information on canopy water status is proposed in terms of the distinction of at least two seasonal classes of irrigated crops, one of spring and one of summer growing cycles.

    The HIRLAM performance evaluation reveals model shortcomings essentially in four areas. The moisture assimilation makes the model surface and ABL too moist. The ABL entrainment description cannot resolve the observed temporal and spatial variations of entrainment moisture fluxes. The landuse and soil classification with its associated physiographic database attribute too much green vegetation to the EFEDA grid cells, thus causing a wet bias in the surface energy balance. The aerosol parameterization in the radiation code does not account for the typically higher aerosol load of semiarid environments, which introduces a high bias in solar and net radiation. Practical steps for model improvement are proposed. They focus on the landuse classification and the aerosol parameters, both adapted to dry Mediterranean landscapes.

    Land cover and the climate system
    Hutjes, R.W.A. ; Kabat, P. ; Dolman, A.J. - \ 2003
    In: Global environmental change and land use / Dolman, A.J., Verhagen, A., Rovers, C.A., Dordrecht : Kluwer - ISBN 9781402013461 - p. 73 - 110.
    landgebruik - vegetatie - landbouwklimatologie - klimaatverandering - bodemwater - ontbossing - woestijnvorming - land use - vegetation - agroclimatology - soil water - deforestation - desertification - climatic change
    Catastrophic vegetation dynamics and soil degradation in semi-arid grazing systems
    Rietkerk, M. - \ 1998
    Agricultural University. Promotor(en): L. Stroosnijder; H.H.T. Prins. - S.l. : s.n. - ISBN 9789054859413 - 155
    beweidingssystemen - aride klimaatzones - bodemdegradatie - woestijnvorming - vegetatie - bodemwater - sahel - tanzania - burkina faso - grazing systems - arid zones - soil degradation - desertification - vegetation - soil water - sahel - tanzania - burkina faso - cum laude

    When vegetation is drastically reduced as a result of drought or an increase in herbivore numbers, it does not simply recover if periods with normal rainfall follow or if herbivores are removed. These are commonly recognized catastrophic phenomena of semi-arid grazing systems in general and of the African Sahel in particular. The main aims of this thesis are to provide an effective explanation of the catastrophic properties of vegetation dynamics in these systems and to predict under which conditions they might be expected.

    We start with a description of Sahelian rangeland vegetation dynamics, to reveal its catastrophic properties. This exercise appeared a very useful first step in the growth of our ideas about catastrophic vegetation dynamics because: 1) it translated rather vague concepts into a verifiable format by deducing hypotheses about the conditions under which catastrophic vegetation dynamics might be expected, and 2) it generated the notion that soil degradation could somehow be an important factor attributing to catastrophic vegetation dynamics in semi-arid grazing systems. This is in contrast with models that emphasize herbivore feeding characteristics or plant competition as possible mechanisms underlying catastrophic vegetation dynamics. We tested the hypothesis that soil degradation, i.e. soil erosion by run-off and wind and the consequent loss of water and nutrients, is sufficient to explain catastrophic vegetation dynamics by mathematical modelling.

    Our model studies indeed show that soil degradation can effectively explain the catastrophic properties of semi-arid grazing systems. Soil degradation can cause a positive feedback between reduced resource (soil water and nutrients) availability and reduced vegetation biomass which may lead to collapse of the system. This positive feedback loop can be triggered by grazing. We argue on the basis of a large body of literature that this is an important mechanism causing catastrophic vegetation dynamics in semi-arid grazing systems. Furthermore, our model studies predict for which site-specific properties catastrophic vegetation dynamics may be expected, that is on loamy or clayey soils in case of water-limited vegetation biomass production, and on sandy soils in case of nutrient-limited biomass production. This is because sandy soils have higher water infiltration rates but are more vulnerable to nutrient loss through erosion than loamy or clayey soils.

    Based on our models, we hypothesized that the removal of aboveground herbaceous biomass would lead to a reduced soil water content and biomass production because of reduced water infiltration and increased run-off. We tested this hypothesis in a semi-arid savanna in Tanzania (East Africa). Indeed, as a consequence of biomass removal, a reduction in soil water content and biomass production occurred. But it appeared that increased loss of soil water through increased soil evaporation as a consequence of litter removal ultimately outbalanced all other effects on soil water content. Several factors might have contributed to the importance of increased soil evaporation, overriding that of reduced water infiltration and increased run-off. The soil in the research area was a sandy loam, with higher water infiltration rates than soils with a lower percentage sand and higher perentage clay, while rainfall primarily occurred in light showers. Thus, under these conditions, when the positive feedback between reduced water infiltration and reduced biomass does not operate, another positive feedback that is between increased soil evaporation and reduced biomass may become prominent.

    We further hypothesized that at a certain range of herbivore impact small initial differences in plant cover and amount of soil resources can magnify to alternative states which persist in time due to positive plant-soil feedbacks. We tested this hypothesis in a semi-arid grazing system in Burkina Faso (West Africa), where we studied vegetation patchiness along a gradient of herbivore impact. Indeed, the occurrence and likely persistence of a spatial pattern of vegetated patches alternating with bare soil at a certain range of herbivore impact could be explained by the positive plant-soil feedback between vegetation biomass and water infiltration.

    We stress the general applicability of our models by comparing catastrophic vegetation dynamics of the semi-arid grasslands of the African Sahel with the arctic salt marshes along the Hudson Bay in Canada. We argue that in both systems, an increase of herbivory triggered a catastrophic vegetation shift, which was ultimately caused by a positive plant-soil feedback, leading to desertification.

    One of our model assumptions was that herbivore density is not regulated by vegetation biomass. In the general discussion, I investigated the influence of a positive feedback between vegetation biomass and water infiltration on the dynamics of a plant-herbivore system, where herbivore density depends on vegetation biomass. As a consequence of the positive feedback and if herbivore reproduction is efficient, I predict that the plant-herbivore system could destabilize and collapse. In this chapter I also stress the practical relevance of our studies as our approach may finally lead to objective ecological criteria on which pastoral managers can base their decision how to evade the hazard of degradation of their rangelands.

    I highlight three topics which deserve more priority on the reseach agenda concerning semi-arid grazing systems in the near future. Hereby, I want to stress that it is important to put experimental and empirical studies into a clear theoretical framework, whereby mathematical modelling should play an important role. The three topics are:

    1. spatial heterogeneity and vegetation pattern formation,

    2. facilitation and competition between functional plant groups within the herbaceous layer and

    3. the effects of positive plant-soil feedbacks on herbivore dynamics.
    Catastrophic vegetation shifts and soil degradation in terrestrial grazing systems.
    Koppel, J. van de; Rietkerk, M. ; Weissing, F.J. - \ 1997
    Trends in Ecology and Evolution 12 (1997)8. - ISSN 0169-5347 - p. 352 - 356.
    natuurlijke graslanden - extensieve weiden - plantensuccessie - vegetatie - milieuafbraak - woestijnvorming - overexploitatie - natural grasslands - rangelands - plant succession - vegetation - environmental degradation - desertification - overexploitation
    It has long been recognized that alternative vegetation states may occur in terrestrial grazing systems. This phenomenon may be of great importance as small environmental fluctuations may lead to relatively sudden and irreversible jumps between vegetation states. Early theoretical studies emphasized saturation of herbivore feeding to explain multiple stable states and catastrophic behaviour. Recent studies on semi-arid grasslands and arctic salt marshes, however, relate catastrophic events in these systems to plant-soil interactions.
    Irrigation and the environment of the Aral Sea basin : an annotated bibliography
    Trouw, L.A. - \ 1994
    Wageningen : ILRI - 78
    irrigatie - watervoorziening - waterbeheer - watervoorraden - milieu - verontreinigende stoffen - verontreiniging - nadelige gevolgen - vegetatie - milieuafbraak - woestijnvorming - ruimtelijke ordening - landgebruik - zonering - kazachstan - hydrologie - overexploitatie - irrigation - water supply - water management - water resources - environment - pollutants - pollution - adverse effects - vegetation - environmental degradation - desertification - physical planning - land use - zoning - kazakhstan - hydrology - overexploitation
    Participatie in milieuprojecten in West Afrika.
    Dijk, H. van; Bruijn, M. de - \ 1989
    Leiden : Leiden University (Memoranda "Environment and development" 3) - 118
    woestijnvorming - ontwikkelingsprojecten - milieuafbraak - mali - natuurlijke hulpbronnen - niger - planning - bescherming - herstel - hulpbronnengebruik - plattelandsontwikkeling - plattelandsplanning - sociale economie - duurzaamheid (sustainability) - vegetatie - economische planning - overexploitatie - desertification - development projects - environmental degradation - mali - natural resources - niger - planning - protection - rehabilitation - resource utilization - rural development - rural planning - socioeconomics - sustainability - vegetation - economic planning - overexploitation
    The struggle of the green against the yellow dragon : the Chinese approach to desertification control and its usefulness for the Sahel
    Breman, H. - \ 1987
    Wageningen : CABO - 62
    china - woestijnvorming - milieuafbraak - erosiebestrijding - bedrijfssystemen - flora - landgebruik - natuurlijke hulpbronnen - ruimtelijke ordening - planten - bescherming - herstel - hulpbronnengebruik - sahel - bodembescherming - duurzaamheid (sustainability) - vegetatie - oogsttoename - oogstverliezen - opbrengsten - zonering - overexploitatie - china - desertification - environmental degradation - erosion control - farming systems - flora - land use - natural resources - physical planning - plants - protection - rehabilitation - resource utilization - sahel - soil conservation - sustainability - vegetation - yield increases - yield losses - yields - zoning - overexploitation
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