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Op proefcomplex de Veenkampen in het Wageningse Binnenveld wordt door verschraling, vernatting en afplaggen geprobeerd de groeicondities en botanische rijkdom terug te krijgen van de vroegere blauwgraslanden (Cirso-Molinietum). De tot nu toe bereikte resultaten van het herstelbeheer worden vergeleken met gegevens uit oud graslandonderzoek m.b.t. botanische samenstelling, bodemvruchtbaarheid, graslandproductie en nutrientengehaltes. Is met dit beheer herstel wel mogelijk?

Een sinds 1899 als uitgestorven beschouwde inheemse plant van natte graslanden werd opnieuw ontdekt op een kleidam langs de Maas bij Stevensweert (Limburg). Beschrijving, historisch voorkomen in Nederland, groeiplaats, en plantensociologische positie

In 1998 is deze watervaren, bekend als aquariumplant, aangetroffen in een uiterwaard van de Waal in de Bommelerwaard. Dit is 190 km noordelijker dan de tot dusver noordelijkste vindplaats. Verspreiding, achteruitgang, ecologie en plantensociologische aspecten van deze soort van Europese Rode Lijsten

The behaviour of evaporation, sensible heat and canopy conductance of fallow savannah and patterned woodland in the Sahel is studied for the HAPEX-Sahel Intensive Observation Period. Both fallow savannah and patterned woodland reach evaporation rates of 4–5 mm day−1 during the rainy part of the IOP and show a decline, after the rains have ceased, to 2 mm day−1. Sensible heat fluxes are different for the two vegetation types. This is also reflected in the behaviour of the evaporative fraction. Analysis of the vegetation surface conductance of the vegetation part shows that maximum values for fallow savannah are around 10 mm s−1, and for patterned woodland up to 40 mm s−1. The response of the conductance to vapour pressure deficit is different for the two vegetation types. This is attributed to differences in C3 and C4 species composition. The consequences of these differences for modelling vegetation-atmosphere interaction in the semi-arid tropics are discussed.

Verslag van onderzoek in het kader van obn

The variability between surface flux measurements at the fallow sites of the three HAPEX-Sahel supersites is examined over periods of three or four consecutive days. A roving eddy correlation instrument provided a common base for comparison at each supersite. The inhomogeneity of the surface and the instrumental layout did not provide the conditions to allow the separation of the effects of instrument error from those due to the spatial variability of vegetation cover and soil moisture. Surface fluxes of sensible and latent heat and energy balance terms were intercompared at each supersite over summation timescales of 1 hour and 3 days. It is shown that, generally, HAPEX-Sahel hourly sensible heat flux and latent heat values have confidence limits of 15% and 20% respectively. The three-day period energy balance shows the combined sensible and latent heat fluxes to have a confidence limit of 3%. It is concluded that, due to the averaging effect of longer time periods and larger flux footprints on spatial inhomogeneity, confidence in the surface flux measurements increases with longer summation periods and with neutral atmospheric surface layers which characterise the rainy period of the Intensive Observation Period.

An airborne laser profiling altimeter was used to measure surface features and properties of the landscape during the HAPEX-Sahel Experiment in Niger, Africa in September 1992. The laser altimeter makes 4000 measurements per second with a vertical resolution of 5 cm. Airborne laser and detailed field measurements of vegetation heights had similar average heights and frequency distribution. Laser transects were used to estimate land surface topography, gully and channel morphology, and vegetation properties ( height, cover and distribution). Land surface changes related to soil erosion and channel development were measured. For 1 km laser transects over tiger bush communities, the maximum vegetation height was between 4-5 and 6-5 m, with an average height of 21 m. Distances between the centre of rows of tiger bush vegetation averaged 100 m. For two laser transects, ground cover for tiger bush was estimated to be 225 and 301 per cent for vegetation greater than 0-5m tall and 190 and 25-8 per cent f...

Een nieuwe, eenvoudige bepaling van de (botanische) kwaliteit van de natuur in Nederland. De resultaten worden weergegeven in de vorm van verspreidingskaarten van 28 ecologische groepen (ecotoopgroepkaarten)

Het jaar 2001 was het twaalfde jaar waarin de Platensoiologische Kring Nederland een aantal botanische excursies organiseerde naar natuurterreinen in Nederland en de ons omringende landen. In dit boekje wordt daar (nu) verslag van gedaan

Het jaar 2001 was het twaalfde jaar waarin de Platensoiologische Kring Nederland een aantal botanische excursies organiseerde naar natuurterreinen in Nederland en de ons omringende landen. In dit boekje wordt daar (nu) verslag van gedaan

Overal ter wereld hebben de verschillende vegetatiestructuren geleid tot aangepaste gebruikers van die vegetatie. De invloed van de gebruikers, met name de grote grazers (herbivoren) op de vegetatie en het landschap wordt in dit artikel belicht

Within the framework of the Dutch `Network Ecological Monitoring¿, a large set of new permanent plots has been established to monitor selected plant communities throughout The Netherlands for studying the effects of environmental changes on species composition of semi-natural communities. This national programme will also make use of pre-existing permanent plots. These plots reflect the long and comprehensive history of research using permanent plots in The Netherlands, where the first permanent plots were established in the early 1930s. To enhance the usefulness of pre-existing permanent plots, a comprehensive permanent plot database was compiled. This database was derived from the Dutch National Vegetation Database, that was established for the recent vegetation classification of The Netherlands. This was supplemented with information from various organizations and a number of individual researchers. Currently, the permanent plot database contains ca. 6000 permanent plots. More than 2500 of these plots have been sampled at least 5 ×, and ca. 1500 plots at least 10 ×. Most of the plots are from grasslands, followed by forests and dune systems. This database not only provides insight into vegetation succession, fluctuations within plant communities over time, and the effects of changes of the environment on the vegetation but, indirectly, it also offers the possibility of studying the long-term behaviour of individual plant species (e.g. establishment, competition, longevity). For the Network Ecological Monitoring a selection of these (historical) plots will be added to the new network of permanent plots in The Netherlands, thus supplying information of past vegetation conditions

Op proefcomplex de Veenkampen in het Wageningse Binnenveld wordt door verschraling, vernatting en afplaggen geprobeerd de groeicondities en botanische rijkdom terug te krijgen van de vroegere blauwgraslanden (Cirso-Molinietum). De tot nu toe bereikte resultaten van het herstelbeheer worden vergeleken met gegevens uit oud graslandonderzoek m.b.t. botanische samenstelling, bodemvruchtbaarheid, graslandproductie en nutrientengehaltes. Is met dit beheer herstel wel mogelijk?

Op proefcomplex de Veenkampen in het Wageningse Binnenveld wordt door verschraling, vernatting en afplaggen geprobeerd de groeicondities en botanische rijkdom terug te krijgen van de vroegere blauwgraslanden (Cirso-Molinietum). De tot nu toe bereikte resultaten van het herstelbeheer worden vergeleken met gegevens uit oud graslandonderzoek m.b.t. botanische samenstelling, bodemvruchtbaarheid, graslandproductie en nutrientengehaltes. Is met dit beheer herstel wel mogelijk?

In 1998 is deze watervaren, bekend als aquariumplant, aangetroffen in een uiterwaard van de Waal in de Bommelerwaard. Dit is 190 km noordelijker dan de tot dusver noordelijkste vindplaats. Verspreiding, achteruitgang, ecologie en plantensociologische aspecten van deze soort van Europese Rode Lijsten

In 1998 is deze watervaren, bekend als aquariumplant, aangetroffen in een uiterwaard van de Waal in de Bommelerwaard. Dit is 190 km noordelijker dan de tot dusver noordelijkste vindplaats. Verspreiding, achteruitgang, ecologie en plantensociologische aspecten van deze soort van Europese Rode Lijsten

Een sinds 1899 als uitgestorven beschouwde inheemse plant van natte graslanden werd opnieuw ontdekt op een kleidam langs de Maas bij Stevensweert (Limburg). Beschrijving, historisch voorkomen in Nederland, groeiplaats, en plantensociologische positie

In this thesis the work of the author on the modelling of radiative transfer in vegetation canopies and the terrestrial atmosphere is summarized. The activities span a period of more than fifteen years of research in this field carried out at the National Aerospace Laboratory NLR.For the interpretation of optical remote sensing observations of vegetation canopies from satellites or aircraft the use of simulation models can be an important tool, as these models give insight in the relations between vegetation properties and observed remote sensing data.The models discussed here are first presented from a theoretical point of view. An attempt has been made to construct a framework in which all the discussed models, for vegetation as well as for the atmosphere, can be represented. After an introduction on basic radiometric quantities and relations (chapter 2), and a classification of radiative transfer models and solution methods (chapter 3), examples of existing models are discussed in chapter 4.In chapter 5 a new generalized theory of radiative transfer models for azimuthally isotropic media is presented, namely the (N+2)-stream theory. This theory describes radiative transfer in vegetation canopies or atmospheres to any desired numerical accuracy. In the formulation of the analytical solution of this model, which is based on eigenvector decomposition, much attention has been paid to possible numerical problems. Symmetry relations are exploited in order to reduce memory requirements and computation time, and expressions have been found for which the so-called reciprocity relations are automatically fulfilled. The numerical capabilities of this model for simulation of atmospheric radiative transfer are demonstrated in chapter 6.The theory of the vegetation canopy bidirectional reflectance models SAIL and SAILH are discussed in chapters 7 and 8. Both are four-stream models. In SAILH the so-called hot spot effect, which is related with the finite leaf size, is incorporated. After these more theoretic chapters, practical aspects of the radiative transfer models are discussed in the following chapters.In chapter 9 the application of a four-stream atmosphere model to the correction and calibration of Landsat Thematic Mapper images is demonstrated. This atmosphere model has been coupled with the SAILH model into an overall four-stream model of optical remote sensing observations from any altitude. This model is called OSCAR (optical soil-canopyatmosphere radiance) and is presented in chapter 10.Applications of radiative transfer modelling to optical remote sensing problems are illustrated in chapter 11, and chapter 12, summarizes the conclusions of this thesis.

In this thesis the work of the author on the modelling of radiative transfer in vegetation canopies and the terrestrial atmosphere is summarized. The activities span a period of more than fifteen years of research in this field carried out at the National Aerospace Laboratory NLR.For the interpretation of optical remote sensing observations of vegetation canopies from satellites or aircraft the use of simulation models can be an important tool, as these models give insight in the relations between vegetation properties and observed remote sensing data.The models discussed here are first presented from a theoretical point of view. An attempt has been made to construct a framework in which all the discussed models, for vegetation as well as for the atmosphere, can be represented. After an introduction on basic radiometric quantities and relations (chapter 2), and a classification of radiative transfer models and solution methods (chapter 3), examples of existing models are discussed in chapter 4.In chapter 5 a new generalized theory of radiative transfer models for azimuthally isotropic media is presented, namely the (N+2)-stream theory. This theory describes radiative transfer in vegetation canopies or atmospheres to any desired numerical accuracy. In the formulation of the analytical solution of this model, which is based on eigenvector decomposition, much attention has been paid to possible numerical problems. Symmetry relations are exploited in order to reduce memory requirements and computation time, and expressions have been found for which the so-called reciprocity relations are automatically fulfilled. The numerical capabilities of this model for simulation of atmospheric radiative transfer are demonstrated in chapter 6.The theory of the vegetation canopy bidirectional reflectance models SAIL and SAILH are discussed in chapters 7 and 8. Both are four-stream models. In SAILH the so-called hot spot effect, which is related with the finite leaf size, is incorporated. After these more theoretic chapters, practical aspects of the radiative transfer models are discussed in the following chapters.In chapter 9 the application of a four-stream atmosphere model to the correction and calibration of Landsat Thematic Mapper images is demonstrated. This atmosphere model has been coupled with the SAILH model into an overall four-stream model of optical remote sensing observations from any altitude. This model is called OSCAR (optical soil-canopyatmosphere radiance) and is presented in chapter 10.Applications of radiative transfer modelling to optical remote sensing problems are illustrated in chapter 11, and chapter 12, summarizes the conclusions of this thesis.

Het Geontegreerd Ruimtelijk Evaluatie-instrumentarium voor Natuurontwikkelingsscenario's is gebaseerd op een samenhangende structuur van modellen die met elkaar communiceren via een database die is gekoppeld aan een geografisch informatiesysteem. De structuur, de methodiek en de werking van het datamodel worden beschreven. De modellen simuleren de regionale waterhuishouding, de zuur- en nutriëntenhuishouding en de vegetatieontwikkeling. Rekenresultaten worden weggeschreven naar het datamodel. Via hetdatamodel worden scenario's gegenereerd voor atmosferische depositie, regionale waterhuishouding en natuurontwikkeling. De scenario's worden geëvalueerd op kansrijkdom met een natuurtechnisch model dat natuurwaarden berekent.

Het Geontegreerd Ruimtelijk Evaluatie-instrumentarium voor Natuurontwikkelingsscenario's is gebaseerd op een samenhangende structuur van modellen die met elkaar communiceren via een database die is gekoppeld aan een geografisch informatiesysteem. De structuur, de methodiek en de werking van het datamodel worden beschreven. De modellen simuleren de regionale waterhuishouding, de zuur- en nutriëntenhuishouding en de vegetatieontwikkeling. Rekenresultaten worden weggeschreven naar het datamodel. Via hetdatamodel worden scenario's gegenereerd voor atmosferische depositie, regionale waterhuishouding en natuurontwikkeling. De scenario's worden geëvalueerd op kansrijkdom met een natuurtechnisch model dat natuurwaarden berekent.

Verslag van onderzoek in het kader van obn

Overal ter wereld hebben de verschillende vegetatiestructuren geleid tot aangepaste gebruikers van die vegetatie. De invloed van de gebruikers, met name de grote grazers (herbivoren) op de vegetatie en het landschap wordt in dit artikel belicht

Overal ter wereld hebben de verschillende vegetatiestructuren geleid tot aangepaste gebruikers van die vegetatie. De invloed van de gebruikers, met name de grote grazers (herbivoren) op de vegetatie en het landschap wordt in dit artikel belicht

This paper argues that not only should environmental and ecological benefits and economic costs be considered in developing nature conservation policies at the farm level but that farmers' perceptions should also be taken into account. Statistical analysis of survey data demonstrates the relevance of these behavioural aspects. Arable farmers with experience of unsprayed crop edges indicated that they preferred unsprayed edges in cereals or grass strips for agronomical, farming equipment related and socio-psychological reasons. The study also focused on the “ideal” unsprayed crop edge from the farmers' perspective. It appeared that a flexible width is most important for acceptance in farming practice, because it is, above all, the width that determines compatibility with existing farming organisation and parcel lay-out. In this respect, there was significant differences between regions. With regard to the payment system, farmers prefer a guaranteed reward instead of a “payment for nature” result, irrespective of the region considered.

Changes in vegetation are often caused by changes in abiotic site factors, such as pH, nitrogen availability and soil moisture. It has been recognized that abiotic site factors are affected by atmospheric deposition and groundwater-table changes. In order to evaluate the effects of eutrophication, acidification and desiccation on site factors, the model SMART2 has been developed. For the Netherlands combinations of two acidification and two seepage scenarios (1990–2050) were evaluated with SMART2. The results are focused on pH, nitrogen availability and base saturation. Calculations were made for combinations of five vegetation structures on seven soil types and the five groundwater-table classes, using a 1 km2 grid. Results showed that deposition reductions lead to a relatively fast improvement of the site factors, increase in pH and base saturation and decrease in N availability. Whereas a reduction in groundwater abstractions of 25% has little or no effect on the pH and N availability.

The Terrestrial Vegetation Model (TVM) of the Integrated Model to Assess the Greenhouse Effect ( image 2.0) determines potential land cover for natural ecosystems and potential productivity for agrosystems. A model analysis of this TVM using Monte Carlo simulations is described for the eighteen Costa Rican (0.5° × 0.5° latitude-longitude) image 2.0 grid cells. It is demonstrated that the TVM is not overly sensitive to climate input variability. Much observed output variability is related to model parameters. These model parameter related effects can strongly determine the intra/inter grid variability for Costa Rican potential yields. The model analysis indicates that more model refinement is required to make any effort to improve data quality effective. It is therefore proposed to remove as many model criteria as possible or to replace them by more gradual criteria based on crop ecophysiological characteristics. A first tentative comparison of maize, rice and pulses yield potentials and their distribution in Costa Rica during 1973 and 1984, suggests that the assumption that the two are related, as assumed in the Land Cover Model (LCM) in image 2.0, has some validity.

This paper is concerned with subpixel modelling of land cover estimation. A new method is presented to estimate the abundance of different cover types within individual pixels. Several linear and non-linear multivariate calibration techniques are compared with respect to their ability to establish a relation between pixel values and fractions of ground cover. The method is demonstrated using Landsat-TM imagery and data from Dutch heathlands. By using an optimization procedure for matching field data to image data, a solution was found for the problem of positioning errors in the training set formation.

Changes in vegetation are often caused by changes in abiotic site factors. The SMART2 model has been developed to evaluate the effects of changes in ion inputs by atmospheric deposition and seepage on these site factors. Linkage with the Multiple Stress Model for Vegetation (MOVE) enables evaluation of the effects on the occurrence probability of vegetation species in response to deposition and seepage scenarios. Combinations of two deposition and two seepage scenarios were evaluated with SMART2. Results focused on pH, nitrogen availability and base saturation. Effects of changes in pH on the occurrence probability of forest understorey in a nutrient-poor deciduous forest were evaluated with MOVE.