Search

BackgroundIt is generally unknown to what extent organ transplant recipients can be physically challenged. During an expedition to Mount Kilimanjaro, the tolerance for strenuous physical activity and high-altitude of organ transplant recipients after various types of transplantation was compared to non-transplanted controls.MethodsTwelve organ transplant recipients were selected to participate (2 heart-, 2 lung-, 2 kidney-, 4 liver-, 1 allogeneic stem cell-and 1 small bowel-transplantation). Controls comprised the members of the medical team and accompanying family members (n = 14). During the climb, cardiopulmonary parameters and symptoms of acute mountain sickness were recorded twice daily. Capillary blood analyses were performed three times during the climb and once following return.ResultsEleven of the transplant participants and all controls began the final ascent from 4700 meters and reached over 5000 meters. Eight transplant participants (73%) and thirteen controls (93%) reached the summit (5895m). Cardiopulmonary parameters and altitude sickness scores demonstrated no differences between transplant participants and controls. Signs of hyperventilation were more pronounced in transplant participants and adaptation to high-altitude was less effective, which was related to a decreased renal function. This resulted in reduced metabolic compensation.ConclusionOverall, tolerance to strenuous physical activity and feasibility of a high-altitude expedition in carefully selected organ transplant recipients is comparable to non-transplanted controls.

For the semi-detailed characterization of inland valleys systems in the Ivory Coast, transect sampling was used to describe valley morphology, soils, and land use characteristics. Initially, for each valley one transect with a width of 200 to 400 m was proposed. More recently, use of a larger number of transects has been suggested. However, there is no statistical basis for either the number of transects to be described or their optimal width. Two sets of aerial photographs (1979, scale 1:50 000, and 1996, scale 1:20 000) of the Boundiali key area were processed and the results digitized. Using GIS, sets of transects with different width were made, and used for the determination of the sample size for estimating the land use ratio and the valley bottom ratio at valley system level with given confidence intervals. These results were validated with data from the field and with sets of pre-selected transects. The calculated sample size is based on simple random sampling and depends on both transect width and variability in the study area. For the characterization of inland valleys with reasonable confidence intervals, the sample size for random sampling is too large for the semi-detailed characterization method. Smaller samples of transects selected on the basis of sub-recent aerial photographs gave comparable results for land cover characteristics estimation as the larger samples for random sampling. There is scope for reducing sample size by formalizing criteria for transect placement on the basis of the earlier aerial photographs.

In dit project zullen met MIPS nieuwe procedures ontwikkeld worden voor het conditioneren en acclimatiseren van enten van groentengewassen. Met MIPS kunnen de effecten van conditionering en acclimatisering op groei, stress en stressgevoeligheid van de enten in de kas nauwkeurig en snel gemeten worden. Op deze wijze wordt een flink aantal conditionering/acclimatisering combinaties in relatief korte tijd geanalyseerd. Uiteindelijk zal uit deze combinaties een aantal geselecteerd worden voor evaluatie en validatie onder praktijkcondities.

In dit project zullen met MIPS nieuwe procedures ontwikkeld worden voor het conditioneren en acclimatiseren van enten van groentengewassen. Met MIPS kunnen de effecten van conditionering en acclimatisering op groei, stress en stressgevoeligheid van de enten in de kas nauwkeurig en snel gemeten worden. Op deze wijze wordt een flink aantal conditionering/acclimatisering combinaties in relatief korte tijd geanalyseerd. Uiteindelijk zal uit deze combinaties een aantal geselecteerd worden voor evaluatie en validatie onder praktijkcondities.

Building on past classifications, this article proposes a comprehensive characterization of rice-growing environments in West Africa on the basis of ecological and agronomic parameters. Using climate, soils, toposequence, land types and rice cropping system as classificatory principles, 18 different environments are distinguished and their characteristics are summarized in three sets of tables. Current constraints to rice production in each of the environments and the implications for rice research are briefly highlighted, as well as the need for field-level verification of the characterization.

From 1995 until July 1st, 2005, the CAMASE Register of Agro-ecosystems Models was available as a searchable database on the Internet, hosted by Wageningen UR Library. This electronic-only edition of the Register contains the data present in the Register after the final update in June 1996.

From 1995 until July 1st, 2005, the CAMASE Register of Agro-ecosystems Models was available as a searchable database on the Internet, hosted by Wageningen UR Library. This electronic-only edition of the Register contains the data present in the Register after the final update in June 1996.

LUSA (Land Use Systems Analysis), a new methodology to develop sustainable agro-ecosystems as part of land-use planning, combines high-tech assessment methodologies, such as multicriteria computer models, with participatory methodologies. LUSA has been tested in Sub-Saharan West Africa

In vitro techniques have been introduced in potato seed production systems in recent years. This research project aimed at studying the morphological and physiological changes in plants and crops in the last three phases of a seed production system that included an in vitro multiplication, an in vitro normalisation (growing cuttings to rooted plantlets), a transplant production, and a tuber production (field) phase.Leaf area was identified as an important plant parameter for plant growth in the normalisation and transplant production phases. Explants and plantlets with larger initial leaf area performed better than those with smaller initial leaf area. In vitro treatments mainly affected leaf area of transplants through their effects on early above-ground leaf area. Leaf area increase was better described by logistic than by exponential or expolinear curves in all phases of growth, suggesting restriction of leaf area increase in all phases.Low temperature decreased leaf and stem dry weights in all phases, and increased tuber fresh and dry yields, average tuber weight, leaf/stem ratio, specific leaf area and harvest index in the tuber production phase. Growing in vitro plants at low normalisation temperatures increased leaf and total plant dry weights early in the transplant production and tuber production phases. It resulted in higher tuber yields, heavier individual tubers and higher harvest index.Fertilising plants with higher nitrogen (40 versus 10 mg N per plant) during transplant production resulted in plants with higher groundcover in the field. This led to higher interception of solar radiation and higher tuber yield in one of the two experiments. Growing plants at higher temperature (26/20 versus 12/18 °C) during transplant production increased leaf area at the end of the transplant production phase. After transplanting to the field, it resulted in crops with higher groundcover, which intercepted more incoming solar radiation. Yield tended to be higher, but differences could not be assessed as statistically significant. A glasshouse experiment showed that high temperature during transplant production increased leaf and stem dry weights in the tuber production phase, but reduced tuber dry weights and harvest index when temperatures during tuber production were high. Thus, high temperature during transplant production may favour haulm growth and light interception in the field, but may also reduce dry matter partitioning to tubers.Conditions in the tuber production phase were found to be of greater importance for final yield than conditions and treatments in earlier phases.Strategies to optimise the production and use of propagules and transplants should focus on achieving leafy starting material, reducing stress during changes in environment and optimising conditions during tuber production. Production of transplants should be adjusted to the expected growth conditions in the tuber production phase.Key words:Solanum tuberosum L., in vitro plantlet, seed production, normalisation, transplant production, tuber production, acclimatisation, leaf area, groundcover, logistic growth, temperature, nitrogen, dry matter production, specific leaf area, harvest index, radiation interception, radiation use efficiency.

In vitro techniques have been introduced in potato seed production systems in recent years. This research project aimed at studying the morphological and physiological changes in plants and crops in the last three phases of a seed production system that included an in vitro multiplication, an in vitro normalisation (growing cuttings to rooted plantlets), a transplant production, and a tuber production (field) phase.Leaf area was identified as an important plant parameter for plant growth in the normalisation and transplant production phases. Explants and plantlets with larger initial leaf area performed better than those with smaller initial leaf area. In vitro treatments mainly affected leaf area of transplants through their effects on early above-ground leaf area. Leaf area increase was better described by logistic than by exponential or expolinear curves in all phases of growth, suggesting restriction of leaf area increase in all phases.Low temperature decreased leaf and stem dry weights in all phases, and increased tuber fresh and dry yields, average tuber weight, leaf/stem ratio, specific leaf area and harvest index in the tuber production phase. Growing in vitro plants at low normalisation temperatures increased leaf and total plant dry weights early in the transplant production and tuber production phases. It resulted in higher tuber yields, heavier individual tubers and higher harvest index.Fertilising plants with higher nitrogen (40 versus 10 mg N per plant) during transplant production resulted in plants with higher groundcover in the field. This led to higher interception of solar radiation and higher tuber yield in one of the two experiments. Growing plants at higher temperature (26/20 versus 12/18 °C) during transplant production increased leaf area at the end of the transplant production phase. After transplanting to the field, it resulted in crops with higher groundcover, which intercepted more incoming solar radiation. Yield tended to be higher, but differences could not be assessed as statistically significant. A glasshouse experiment showed that high temperature during transplant production increased leaf and stem dry weights in the tuber production phase, but reduced tuber dry weights and harvest index when temperatures during tuber production were high. Thus, high temperature during transplant production may favour haulm growth and light interception in the field, but may also reduce dry matter partitioning to tubers.Conditions in the tuber production phase were found to be of greater importance for final yield than conditions and treatments in earlier phases.Strategies to optimise the production and use of propagules and transplants should focus on achieving leafy starting material, reducing stress during changes in environment and optimising conditions during tuber production. Production of transplants should be adjusted to the expected growth conditions in the tuber production phase.Key words:Solanum tuberosum L., in vitro plantlet, seed production, normalisation, transplant production, tuber production, acclimatisation, leaf area, groundcover, logistic growth, temperature, nitrogen, dry matter production, specific leaf area, harvest index, radiation interception, radiation use efficiency.

As the result of a recent BBSRC-funded workshop between soil scientists, modellers, statisticians and others to discuss issues relating to the derivation of complex environmental models, a set of modelling guidelines is presented and the required associated research areas are discussed.

In this report, methods are developed to estimate yield potentials of biomass crops in various regions within the European Union (EU-12). Different production levels are considered; firstly, the potential production level that can be realized when the crop is optimally supplied with water and nutrients and free from pests, diseases and weeds. Secondly, the so-called water-limited production level is recognized. In the water-limited situation, nutrients are in optimal supply and the crop is free of pests, diseases and weeds, but yield is limited by the availability of water

In this report, methods are developed to estimate yield potentials of biomass crops in various regions within the European Union (EU-12). Different production levels are considered; firstly, the potential production level that can be realized when the crop is optimally supplied with water and nutrients and free from pests, diseases and weeds. Secondly, the so-called water-limited production level is recognized. In the water-limited situation, nutrients are in optimal supply and the crop is free of pests, diseases and weeds, but yield is limited by the availability of water

This article contributes to the development of a general applicable method to characterise landscapes by presenting a technique to obtain data on actual land use by means of transect surveys and farmer interviews. This technique is developed as an alternative to existing ones which generate data on land use mainly as a by-product. As part of a multiscale agro-ecological characterisation methodology, the Integrated Transect Method (ITM) generates data at the semi-detailed level, and bridges gaps between disciplines, scales, and agro-ecological zones. The method is illustrated using bio-physical results from inland valley agro-ecosystems in two agro-ecological zones in Cote d'Ivoire, West Africa. So-called ‘agro-ecosystem diagrams’ offered scope for easy presentation of collected information. Additionally, various quantified land and land use characteristics were used to scale up data from the level of the transect, via inland valleys and valley systems to the level of the agro-ecological subunit. Application of ITM showed that this technique can be used effectively as a tool to analyse bio-physical differences in land use within landscapes and compare differences between them under different agro-ecological conditions. The required integration of bio-physical and socio-economic parameters, however, is the subject of further study.

This thesis describes mutation breeding and tissue culture techniques developed for accelerated domestication of winged bean ( Psophocarpustetragonolobus (L.) DC.). The tissue culture techniques, which are the first steps towards genetic transformation of the crop, include: (1) direct adventitious shoot formation from the axes of cotyledon explants; (2) direct simultaneous regeneration of adventitious shoots and somatic embryos; and (3) direct somatic embryogenesis on the wounds of cotyledon explants. An optimised mutation breeding technique for economic significance, based on the early selection of chlorophyll mutations generated from gamma-radiated seeds, has been developed. The use of this scheme has resulted in the recovery of seed coat colour mutants which have succesfully served as an indirect method for selecting changes in tannin content and nodulation. A desired mutant with reduced tannin content and improved nodulation was selected.

This thesis describes mutation breeding and tissue culture techniques developed for accelerated domestication of winged bean ( Psophocarpustetragonolobus (L.) DC.). The tissue culture techniques, which are the first steps towards genetic transformation of the crop, include: (1) direct adventitious shoot formation from the axes of cotyledon explants; (2) direct simultaneous regeneration of adventitious shoots and somatic embryos; and (3) direct somatic embryogenesis on the wounds of cotyledon explants. An optimised mutation breeding technique for economic significance, based on the early selection of chlorophyll mutations generated from gamma-radiated seeds, has been developed. The use of this scheme has resulted in the recovery of seed coat colour mutants which have succesfully served as an indirect method for selecting changes in tannin content and nodulation. A desired mutant with reduced tannin content and improved nodulation was selected.

This second progress report focuses on designing a theoretical prototype by linking parameters to methods and designing the methods in this context until they are ready for initial testing. The report focuses also on testing and improving the prototype in general and the methods in particular until the objectives as quantified in the set of parameters have been achieved by pilot groups, regional networks and national networks

This research was inspired by the inability of agricultural research to deal adequately with phenomena of variation, diversity and heterogeneity in agriculture. Although these phenomena were observed as long ago as the beginning of this century, they are still causing concern. Until recently, analysis of variance was applied to any form of undesired variation in the experimental results. The statistical elimination of variation from the research coincided with attempts to uniformise agriculture in order to optimise production. For a long time, deviations from the standardised average were regarded as undesirable random effects.Recent research has shown that variations in yield are very common in agroecosystems. They may be large, especially under difficult climatic conditions, and may even be considered as an asset to farmers. There is evidence that variations are not random, but are the result of systematic interaction between environment, crop genotype and management. This agrodiversity has important relations with the higher-level heterogeneity of the environment and diversity of farm households. At present, no comprehensive approach to its analysis is available, largely because agrodiversity is basically multidimensional in nature and may comprise several levels of aggregation.The objective of this study was to contribute to the understanding of diversity in agroecosystems by focusing explicitly on variations of yield and their explanation at field and household level. Between 1991 and 1993, field work was done in one village in northern Cameroon. Yield variations of three crops, field properties, crop and management characteristics and household characteristics were assessed systematically. Various techniques for statistical analysis were employed to determine the magnitude of variation and to define the agrodiversity of Within the agroecosystern of the selected village, variations in yield were observed for rainfed sorghum, cotton and dry season sorghum. The magnitude of variation was more or less constant over the years of observation, but varied between the crops. Two rainfed sorghum cropping systems were distinguished and within one cropping system, three field types were defined according to their distance from the homestead. Thus stratified it was possible to reduce overall yield variation and to explain it within each stratum by a reduced number of variables. It was concluded that the composition of agrodiversity was not uniform over the strata. Yield levels, limitations and constraints of rainfed sorghum production were specific to each cropping system and field type.Of the three crops, yield variation was greatest in cotton, despite many efforts of the cotton agency to standardise its cultivation. This variation was explained by distinguishing between types of variables, each explaining cotton yield variation to a different degree and in a particular way. Dry season sorghum showed least variation in yield, although it is subject to great environmental stress. Crop genotype and management proved to be adapted to one dominant field property, i.e. the water holding capacity of the soil. All farmers, irrespective of ethnic or socio-economic origin, agreed about the need to adjust mouskouari sorghum cultivation to field characteristics that define the water availability. Processes at field level leading to agrodiversity could be summarised by (1) spatial differentiation of the fields, (2) mechanisation of labour and (3) adaptation of cultivation to the environment.Ethnic diversity explained the absolute difference in cotton production, and the distinction between rainfed sorghum cropping systems within the agroecosystem. Socio-economic diversity explained the relative differences in cotton yield, and the distinction between rainfed sorghum field types.Finally, gender differences highlighted variations in rainfed sorghum yields and in non-agricultural income. Gender differences and ethnic and socioeconomic diversity proved to be interrelated, resulting in at least three classes of women farmers.It must be concluded that within one agroecosystem, crop yields may vary considerably. The agrodiversity explaining these variations proves to be cropspecific, One agroecosystern may comprise several cropping systems and field types of the same crop. Agrodiversity is also spatially specific and is largely determined by ethnic and socio-economic diversity and gender differences at household level. The potentials and problems of crops and fields also prove to be specific to the farmer. Within the context of rural development, it is essential to distinguish between well defined target groups in order to prevent interventions from uneffective generalisation. To do so, variation, heterogeneity and diversity must be accepted as realistic phenomena in agroecosystems and considered as an important source of information.

LUSA (Land Use Systems Analysis), a new methodology to develop sustainable agro-ecosystems as part of land-use planning, combines high-tech assessment methodologies, such as multicriteria computer models, with participatory methodologies. LUSA has been tested in Sub-Saharan West Africa

Variation within agro-ecosystems is a universal but complex phenomenon which is present in each of the factors that determine the agro-ecosystem, i.e. the environment, genetic resources and management. Agrodiversity is defined as the variation resulting from the interaction between these factors. This variation manifests itself in many different forms, at different scales and levels of aggregation. Examples show that poor management of agrodiversity in high and low external input agriculture reduces output, output stability, resource-use efficiency and the production potential of the natural resource base. A better understanding of agrodiversity is required to improve its management. Also, analysis of variation in agro-ecosystems requires other approaches in research to be further developed in order to characterize, measure and understand relevant variation.

This second progress report focuses on designing a theoretical prototype by linking parameters to methods and designing the methods in this context until they are ready for initial testing. The report focuses also on testing and improving the prototype in general and the methods in particular until the objectives as quantified in the set of parameters have been achieved by pilot groups, regional networks and national networks

Sources of yield variations within one agroecosystem in a village in northern Gabon were investigated combining biophysical, crop genotype and management characteristics of the fields with ethnic and socio-economic characteristics of the households and the farmers. The study shows that diversity and variation should be regarded as important sources of information instead of eliminating them from research

The various multidisciplinary projects presented in this thesis, in hindsight, all contributed to a new approach to land use planning. Hence, their results are placed in a holistic perspective via this approach. Part A presents a method for characterizing land use on the basis of transect surveys (Côte d'Ivoire; Chapter 2). In Chapter 3, an interactive multiple goal linear programming model is described as a method to quantify natural and human resources, and to analyse the relations between various crop and animal husbandry systems. In Part B, nutrient relations are examined with the aim of arriving at fertilizer recommendations for cereals through field experimentation (Senegal; Chapter 4), and literature review and simulation modelling (Chapter 5). Additionally, the effects of grazing on subshrubs in Egypt are examined by field experiments and simulation to quantify the availability of this feed resource (Chapter 6). Part C shows possible land use options, on the basis of a simulation model for managing integrated small ruminant - barley - subshrub systems (Egypt; Chapter 7), and a multiple goal linear programming model to examine the importance of fertilizer availability for self-sufficiency in food (Mali; Chapter 8). A synthesis (Chapter 9) presents 'Land Use Systems Analysis' after evaluating the current methods of land use planning. The importance of goals, scales, tools, and the time-path for attaining goals are discussed, and recommendations are made for the future application of land use systems analysis.

In this volume of the SARP research proceedings two 'Application Programs' are introduced. Five papers are presented on agro-ecological zonation and characterization, dealing with rainfall mapping, GIS and soil data base investigation. Nine papers are presented on crop rotation optimization, having crop rotation of rice-peanut and barley-rice as subjects

RESEARCH FRAMEWORK:SUSTAINABILITY AS A PLANNING PROBLEMThe quality of soil, water and air, and the number and diversity of plant and animal species in the Netherlands, show a sharp decline. This decline in the quality of the natural substratum poses a major problem for environmental policy and planning. Government policy and planning aim at sustainable land use. However, the concept of sustainability is subject to various interpretations. This study concentrates on the ecological aspects of sustainability. The problem of the current decline in the quality of the natural substratum can be solved only on the basis of knowledge of ecological limits to human management. To this end it is assumed that planning needs an ecological approach, an angle from which ecological aspects of human management can be analysed, and adequate solutions to the problem of the declining quality of the natural substratum can be found. In order to devise sustainable trajectories for the environment, indicators of ecological sustainability are needed together with their limiting values. In addition, an ecological approach should provide planning with insight into the underlying factors. These factors are called the building blocks of sustainability. Finally, knowledge of the implications of respecting ecological limits is prerequisite to planning.In this study, an ecological approach is constructed on the basis of theoretical notions as to the persistence of natural ecosystems.The study focuses on the ecological limits to agricultural management in the pleistocene areas in the Netherlands, as it is here that the decline in the quality of the natural substratum is most dramatic. A distinction is made between agro-ecosystems and nature-ecosystems. Agro-ecosystems are defined as ecosystems whose functioning is regulated with a view to agricultural production. Natureecosystems are defined as ecosystems which are controlled with a view to nature conservation and/or nature expansion.LIMITS TO SUSTAINABILITYThe theoretical concept of persistence of ecosystems with a plural hierarchical organisation is chosen as the basis of the search for ecological limits. The hierarchical organisation of ecosystems results from differences in the speed and spatial scale of processes, relevant to the system as a whole. Within this hierarchical organisation, three dimensions are distinguished. The biotic dimension refers to the hierarchically structured network of species. The functional dimension refers to the hierarchy of processes and functions within the ecosystem. The spatial dimension refers to the hierarchical spatial arrangement of ecosystems and their interrelationships. Each ecosystem is characterized by a specific coherence between the biotic, functional and spatial dimensions. The hierarchical organisation of ecosystems and the coherence between the three dimensions play an important role in the self-regulation of natural ecosystems, notably when they are faced with disturbances. These disturbances are defined as significant changes in the characteristics of an ecosystem, which result, for instance, from changes in environmental factors. In contrast to the concept of stability, the concept of persistence implies the self-regulation of ecosystems that can exist in more than one - equilibrium state or attraction domain and even in a non-equilibrium state. Persistence of hierarchically organised ecosystems is defined as the ability to maintain the characteristic coherence of species, functional aspects and spatial components. When confronted with disturbances, these ecosystems are able to persist by shifting from one attraction domain to another. The possibility of alternative equilibrium states is, however, limited to a specific range of disturbances.Ecological theory focuses mostly on population density or population size, elements of the biotic dimension, as indicators of persistence. Limits to the persistence of natural ecosystems are then defined as limits to fluctuations in these indicators, acceptable with a view to the long-term survival of the population in question. Owing to the coherence between the dimensions of hierarchically organised ecosystems, changes in population density or size are the result of underlying functional, biotic or spatial processes. These processes are therefore regarded as the building blocks of persistence. The extent to which the persistence of ecosystems is threatened is related to the extent to which the limits to changes in these building blocks are exceeded.PERSISTENCE OF AGRO-ECOSYSTEMS AND NATURE-ECOSYSTEMSThe processes in both agro-ecosystems and nature-ecosystems are the same as in natural ecosystems. However, they are regulated by a specific form of human management. Agro and nature-ecosystems differ in the extent to which their selfregulation is replaced by human regulation. It is assumed that these types of ecosystems are also characterized by a three-dimensional hierarchical organisation.In agro-ecosystems, the coherence between the dimensions is regulated with a view to animal and plant production. The yield per ha and/or per animal is regarded as the indicator of the persistence of agro-ecosystems. Important building blocks of the persistence of agro-ecosystems are the quality of the soil in the functional dimension, the health of livestock and crops in the biotic dimension, and the possibility of multiple land use in the spatial dimension.In nature-ecosystems, the coherence between the dimensions is regulated with a view to a specific species composition. The focus is mainly on the conservation of rare species and communities, characteristic for Dutch environmental conditions. This species composition is regarded as the indicator of the persistence of nature-ecosystems. Important building blocks are the quality of soil and groundwater and the level of the groundwater table in the functional dimension, the minimum viable population size of characteristic species, defined as the population size that will ensure (at some statistical level) its persistence for a specified time, in the biotic dimension, and the surface and spatial heterogeneity together with the possibility of connection with similar nature-ecosystems in the spatial dimension.In order to implement an ecological approach for planning, a quantitative indicator of the acceptable limits to the fluctuations in both agricultural yield and species composition is needed. When such an indicator is lacking, this study focuses on limits to changes in the mentioned building blocks, as for example limits to the accumulation of heavy metals in agro-ecosystems and limits to the isolation of nature- ecosystems.AGRO-ECOSYSTEMS AND NATURE-ECOSYSTEMSIN PLEISTOCENE AREASIn order to define the current problems relating to persistence, the relationship between agriculture and nature in pleistocene areas is re-examined through the use of the theoretical framework. The extent to which disturbances in agro and nature- ecosystems threaten their respective persistence depends both on the intensity of agricultural land use, and the susceptibility to related disturbances of the natural substratum, the totality of soil, water, air, plants and animals. Initially, the pleistocene areas were characterized by many gradual transitions from oligotrophic to mesotrophic and eutrophic conditions. The development of agriculture in the pleistocene areas was structurally influenced by the pattern of plains, sand ridges and stream valleys.In the 1960s dairy farming in pleistocene areas expanded enormously. The 1970s showed a large increase in intensive husbandry, especially in the eastern and southern pleistocene areas. Later, a decrease in acreage was compensated by developments in the respective dimensions of agro-ecosystems, resulting in an annually increasing production per hectare and per animal. Factual information concerning possible threats to the persistence of agro-ecosystems is scarce, except for arable farmland in the northern pleistocene area, where agricultural yields show a decline as a result of the intensive tillage practices.Using 'yield' as an indicator of persistence proves to be difficult because of the continuous adjustment and extension of the management of agro-ecosystems. Thus, it is not yet possible to quantify the variation in yields which would be acceptable in terms of persistence. Changes in several building blocks, however, signal possible future threats to the persistence of agro-ecosystems. These changes include the accumulation of potassium and heavy metals in the soil, the speed with which weeds, soil organisms and insects become resistant to pesticides, and the possibility of limited use of land which was heavily manured in the past.Moreover, changes in agricultural land use have affected and still affect other aspects of the quality of the natural substratum through the release of nitrogenous and acidifying compounds, the lowering of the groundwater table and the decrease in spatial heterogeneity.Around 1900, the Dutch nature movement was born out of an increasing concern about the general changes in agricultural land use. In the period 1900-1960 the acreage of nature-ecosystems in the Netherlands sharply decreased. Since 1960, the quality of the remaining nature-ecosystems has been declining. The situation with respect to the number and diversity of species in these nature-ecosystems has deteriorated. Consequently, it is assumed that the persistence of nature-ecosystems in pleistocene areas has been strongly affected. To a large extent, this deterioration is caused by the above mentioned effects of agricultural land use. These disturbing effects have led to a decreasing viability of plants and animals characteristic of nature- ecosystems. As a result of the cumulative effect of disturbances, it can be assumed that nature-ecosystems in. pleistocene areas have only one attraction domain left. This limits their capacity to absorb further disturbances. In order to sustain this assumption, it is necessary to quantify the acceptable variation in species composition for specific types of nature-ecosystems,such as e.g. heaths and moorland pools. So, nature conservation schemes should state explicitly which type of ecosystem is intended. Only then, limits to changes in both the species composition and the relevant building blocks can be determined.From a planning perspective, maintaining the persistence of nature-ecosystems of in the pleistocene areas is a more pressing problem than maintaining the persistence of agro-ecosystems.POLICY PLANS FOR THE QUALITY OF THE NATURAL SUBSTRATUMThe decline in the quality of the natural substratum in the Netherlands prompted the government to revise its policy. In the last few years a number of government reports on this problem have been published: the National Report on Environmental Policy, the Report on Nature Policy, the Third Report on Watermanagement, the Fourth Report on Spatial Organisation (Extra) and the Report on Agricultural Structures. All these reports focus on sustainable development, particularly on the sustainable preservation and development of nature-ecosystems. Besides the traditional preservation of the so-called 'half-natural' ecosystems like heaths and moorlands, there is a strong interest in developing original, self-regulating ecosystems. Restoring the quality of the natural substratum is a prerequisite in both approaches. 'Me different policy plans seek to counteract the current decline in quality by realising both an Ecological Main Structure and a general level of quality of the environment.The above mentioned policy plans are generally lacking in an ecological approach as defined in this study. An explicit definition of sustainability, together with relevant indicators and limiting values, is commonly not given. The objectives as to the quality of the natural substratum have not been made explicit and applicable on the regional level. The reports pay too little attention to the coherence between functional, biotic and spatial conditions for the persistence of ecosystems. Furthermore, the measures proposed to attain the general level of environmental quality are insufficient.BOUNDARY CONDITIONS FOR THE QUALITY OF THE NATURAL SUBSTRATUM IN THE CATCHMENT AREAS OF BEERZE AND REUSELThe case-study evaluates regional plans concerning nature-ecosystems in the catchment areas of two lowland streams in the southern pleistocene area. The pivotal question is whether or not these schemes are adequate in terms of persistence. The case-study comprised three parts: the conservation of forests and heaths as core areas in the Ecological Main Structure, the realisation of corridor zones for forest birds, and the creation of nature expansion areas in stream valleys.The evaluation encountered a number of difficulties. Firstly, the schemes were not very specific about the desired species composition. Secondly, data on the current species composition in potential core areas and nature expansion areas were incomplete. Thirdly, quantitative knowledge as to the limits to fluctuations in the species composition of the nature- ecosystems concerned, is rather limited. Consequently, it proved to be impossible to demarcate entirely the different attraction domains in which these ecosystems can persist.Since an evaluation using the indicator 'species composition' could not be carried out satisfactorily, the study was orientated towards limits to fluctuations in the building blocks of persistence. Again, the knowledge of these limits is patchy. In the functional dimension, the values of the critical loads of acid deposition in nature-ecosystems are in part arbitrary. Knowledge concerning limits to desiccation and eutrophication is limited to estimated original values. In the biotic dimension, no general rule for the minimum viable population size can be given. In the spatial dimension, knowledge concerning the size, location and quality of corridor zones between core areas, required for the dispersal of species, was mostly qualitative.As far as possible, the level of quality of the natural substratum that can be realised on the basis of the proposed policy measures was compared with the level of quality necessary to ensure the persistence of nature-ecosystems. The latter corresponds to the limits on fluctuations in the different building blocks, and is seen as the complex of boundary conditions for persistence. Not only do the results of this comparison show a large gap between measures and conditions, they also suggest that some ecological conditions have not been taken into account at all.Respecting the boundary conditions for the quality of the natural substratum in nature- ecosystems will have far-reaching consequences for the management of the agro-ecosystems in the catchment areas of Beerze and Reusel. These consequences include, in the functional dimension, a reduction of the release of nitrogenous compounds and phosphate, and a reduction of the use of groundwater; in the spatial dimension, a reduction in acreage and in some zones a restriction on land use, due to the requirements of nature-ecosystems; in the biotic dimension, a reduction in the number of animals may be necessary. However, standards for the translation of the conditions for persistence of natureecosystems into acceptable agricultural management have yet to be developed.AN ECOLOGICAL APPROACH TO PLANNINGThe case-study in the Beerze-Reusel area leads to the conclusion that, without an ecological approach, the balance between political objectives, ecological conditions and adequate policies is seriously impeded. The regional plans do not lead to sustainable conservation of existing nature-ecosystems, and the realization of both adequate corridor zones and nature expansion areas in stream valleys seems doubtful. On the other hand, meeting the conditions for the quality of the natural substratum of nature-ecosystems would seriously affect the outlook for agriculture in the Beerze-Reusel area.In theory, combining of the concept of persistence with the hierarchical concept of ecosystems could provide planning with a promising basis for an ecological approach. From this study it is apparent that the coherence between the different ecological aspects of sustainable development necessitates coherence and integration of the different domains of physical planning. The implementation of the theoretical approach elaborated in this study will depend on whether or not the lacunae in ecological knowledge which were encountered can be remedied. In particular there is need for more extensive knowledge of the boundaries of the different attraction domains in which ecosystems can persist.