Landschapsecologie en ruimtelijke organisatie in riviersystemen : een onderzoek naar de landschapsecologie van riviersystemen en de overheidszorg daarvoor in planning en beleid

anglais. Landscape ecological research in the Netherlands has been fruitful because of the mutual exchange of ideas and results of fundamental and applied research. This research project has been focused on methodologies for application of fundamental landscape ecological research in planning for land use and water use with emphasis on nature conservation aspects. The object of research has been the river system, because the river system is both a fundamental landscape ecological unit and an administration unit. The theoretical concept of planning is based on the model of spatial organisation; this model has been worked out by differentiating the rather simple physical aspects into a 'spatial ecological structure'.This model is based on the idea that all species have an ecological web and that these webs together make the - natural - landscape. The main patterns and processes in the spatial ecological structure of river systems are climate and water discharge. Within this context organisms create their ecological webs and these webs together constitute the spatial ecological structure. This spatial ecological structure can be modified by man. Man-through his social organization has an important impact by ecological changes that modify the spatial ecological structure into a manmade physical organisation. It is a model of the interference between sustainability and dynamics. The spatial ecological structure has been used as the guiding principle for the landscape ecological analysis and the interference of landscape ecological processes with changes in society. Within this context the research questions have been formulated as: * the definition of the main processes in river systems that determine ecological development in time and space and its translation into guiding principles and constraints for nature conservation; * evaluation of planning and management of rivers and its related nature in the context of its objectives. To answer these questions several research projects have been carried out, that have all been published in the period 1990-1992. They concerned both questions and emphasised different aspects of the spatial ecological structure. The research projects are: Ecological classification of the climate of the Rhine catchment ( Int. J Biometeorology 1990, 34:194-203 ). In this research an ordination and classification has been carried out on the climate of the Rhine catchment based on data from meteorological stations. The objective of the classification is to provide an ecological interpretation of climate data. The climate of northern France, Belgium, Luxembourg, The Netherlands, The Federal Republic of Germany and northern Switzerland is divided into 5 classes, of which two, the atlantic and the subcontinental are subdivided further into subclasses. The climate classes can be interpreted ecologically and are correlated with floristic and vegetation data. The Rhine valley has a distinctive and characteristic climate. Interpolation of the classification has not been carried out, because of the uneven geographical spread of the sites in the dataset. The position of the Rhine valley as a separate subclass is striking. For the use of climatic data for modelling changes in climate in relation to hydrological effects, this will have minor implications, because the valley is just a section of the total drainage basin. For ecological interpretation of the Rhine catchment however, it will be of major importance, because also climatically the Rhine valley seems to function as a major ecological stream corridor in western Europe. Land use changes or climatic changes in this corridor might improve or hamper its functioning as such. Other rivers do not seem to be characterised by climatic differences in the same way and may not function as climate related stream corridors. They possibly do not have such pronounced effect on the surrounding landscape or insufficient climatic data are lacking to conclude on this. Vegetation, river management and land use in the Dutch Rhine floodplains (Regulated Rivers 1992 7(3):279-289. In this project the relation between vegetation and historical changes in ecological processes has been investigated. The floodplains of the Lower Rhine are situated in a densely populated area of The Netherlands. Although they are intensively used, the floodplains still fulfil important ecological functions. The lower Rhine is the downstream sedimentation zone of the River Rhine and its floodplains are characterised by river transported vascular flora originating from southern and eastern Europe. Using multivariate methods data from literature and field data on grasslands and former river beds have been analyzed to find trends in ecological changes. The consequence of continued sedimentation and diminished erosion is an increased drying out of the floodplains. Excavation and recultivation of former excavated land does not reverse the losses in flora and vegetation. Statistically there is a negative relationship between the characteristic dry fluvial flora and recultivated land. Also the natural transversal river gradient disappears together with its characteristic ecological diversity. Aquatic environments in the floodplains have been changed completely since the regulation works started in the 19th century. Most former river beds have disappeared by silting up. Data on short term vegetation succession confirm the long term analysis of map data. Dutch floodplain policy, regulation of landscape ecological processes ( Landschap 1992 9(l):17-29 ). In this project the relation between floodplain vegetation and the management of ecological processes has been investigated. Rivers are landscape ecological systems, characterised by dynamic processes. Floodplains are very important in the ecological functioning of the river system. The Rhine is a regulated river situated in a densely populated area. The Dutch Lower Rhine is the downstream sedimentation area of the river. Here the floodplains are strongly influenced by man during the last decades. In general there is a process of drying out going on in both the Upper Rhine and the Lower Rhine. River dynamics in the floodplains can be analyzed on basic processes as period and time of discharge, stream velocity, relative altitude and morphology. The importance of the floodplains has been recognised by all administrative levels and nature conservation and nature development has become a policy objective. To develop and execute a river floodplain policy translation of river dynamics into practical planning and management is needed. Little experience is available on the effectiveness of the means for policy execution. The available knowledge shows, that at this moment neither physical planning nor water management but only protection by Nature Conservation Law can be used to handle extreme cases. Conservation of brooks in small watersheds: a case for planning (Landscape and Urban Planning 1990 19:55-68). In this research project a simple regional water balance model has been made of the two regions in the Veluwe in order to qualify the consequences of adjacent land use and urban activities for the objectives of the National Park. Nature conservation is under stress in The Netherlands because of intensive land use and related water use. One of the main problems for the brook systems is planning of water use in order to maintain a locally high water-table. From a study of the water balance it is shown, that extraction in some parts of the research area causes water shortage for brook discharge. Water extraction is inevitable because of the dense population in the fringes of the national park. This leads to the conclusion that integration of research and co-ordination of physical planning and water use planning is needed to realise a sound nature conservation policy for this area. Landscape ecological and spatial impacts of climate change in two areas in the Netherlands (Earth surface processes and Landforms 1991 16:639-652). Possible impact of climatic change on the water balance has been analyzed for the river Dommel and the Veluwe, an area drained by many very small brooks. The water balance has been calculated for the winter and the summer period. With help of four scenarios, based on GCM's, climate data from the dry year 1976 and land use scenarios the impact of climatic change and a possible superposed effect of acid precipitation is analyzed. The results show that although the yearly changes in the water balance are small in some cases, in all cases the fluctuations in the water balance between winter and summer period increase. Changes in precipitation and evapotranspiration are multiplied in water storage and runoff. This will have an important impact on water use planning and management. River systems: a leading part in a changing climate (Milieu 1992 7(3):68-75) A review has been made of research carried out on the impact of climate change in rivers. Climate change will influence the environment in Europe not only by changes in CO 2 -content and temperature, but also by changes in hydrology. Rivers might appear to be very sensitive to climatic variability and climate change. Most important impact is expected to be a change in mean discharge, extreme events and seasonality of runoff, which can cause important changes in erosion and sedimentation in various parts of Europe, quality of both ground water and surface water, functioning of the aquatic and semiterrestrial ecosystems and the availability of water resources. Consequences of climate change combined with potential synergistic effects of acidification will be dealt with sooner or later through the water system in many parts of Europe. Wise use of water, based on thorough analysis of the hydrological system and international co-operation at the level of river catchments are of utmost importance for anticipation on possible changes. From this research it can be concluded, that the natural basis for planning can be considered as a spatial ecological structure made by natural ecological processes and related patterns. Such a framework can be used as a guiding principle for landscape ecological modelling and the analysis of the impact of land use changes. The concept of Ecological Main Structure as developed in The Netherlands is a policy concept. Its scientific basis can be found in the spatial ecological structure of catchments. However, for the pleistocene pail of the Netherlands it can be concluded from the analysis that the objectives of the Dutch Ecological Main Structure can only partly be reached. Natural development can best be achieved for whole catchments because of the strong interaction between all land use. A complicating factor is that all large Dutch rivers and many lowland streams originate from headwaters in other countries. This makes international co-ordination necessary. Dry grasslands in the floodplains of the major dutch rivers are significantly related with sites flooded less than two days a year and significantly not related with excavated and recultivated soils. They are severely under threat of extinction. Former river beds tend to silt up and especially the open oxbows and the tidal oxbows have disappeared. Both tendencies have important consequences for nature conservation strategy in the river area and especially for nature redevelopment projects. The use of physical planning regulations to maintain aquatic nature and wetlands has not yet been very successful, nor in planning nor in implementation and management. Intensive co-operation between the water boards and the municipalities is needed both in planning and in management of waters. The climate of the Rhine catchment can be differentiated into several types among which that of the Rhine valley. This can be of importance for research on the impact of climate change. However, it is not yet clear if other rivers have a comparable corridor. Consequences of climate change combined with potential synergistic effects of acidification will be dealt with sooner or later through the water system in many parts of Europe. Wise use of water, based on thorough analysis of the hydrological system and international co-operation at the level of river catchments are of utmost importance for anticipation on possible changes.

néerlandais; flamand. Welke zijn de belangrijkste processen in riviersystemen die in ruimte en tijd de ecologische ontwikkeling ervan bepalen en kunnen deze processen vertaald worden in uitgangspunten en randvoorwaarden voor natuurbescherming als vorm van landgebruik. Hoe kan c.q. dient in het licht van vergelijking van concrete cases het vigerend ruimtelijk beleid ten aanzien van doelstellingen en implementatie worden beoordeeld?