Staff Publications

Staff Publications

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

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

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

    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 blooming business : Identifying limits to Lake Taihu's nutrient input
Janssen, Annette B.G. - \ 2017
University. Promotor(en): Wolf Mooij, co-promotor(en): J.H. Janse; A.A. van Dam. - Wageningen : Wageningen University - ISBN 9789463431897 - 268
lakes - freshwater ecology - aquatic ecosystems - nutrients - cycling - nutrient flows - biodiversity - algae - models - critical loads - limnology - spatial variation - ecological restoration - china - meren - zoetwaterecologie - aquatische ecosystemen - voedingsstoffen - kringlopen - nutriëntenstromen - biodiversiteit - algen - modellen - limnologie - ruimtelijke variatie - ecologisch herstel

Last century, Lake Taihu (China) became serious eutrophic due to excessive nutrient input. During the 1980s, the first algal blooms emerged in the lake, reaching disastrous proportions in 2007. During that year, the intake of drinking water had to be shut down and millions of people had to look for an alternative source of drinking water. This raises the question whether such problems can be avoided. Of crucial importance in avoiding and reducing toxic algal blooms is the identification of the maximum nutrient load ecosystems can absorb, while remaining in a good ecological state. In this thesis, I aim to determine the critical nutrient load for Lake Taihu. I approach the search for critical nutrient loads of Lake Taihu in five steps with diversity as an overarching topic throughout this thesis: diversity in lakes, diversity in models, diversity in spatial distribution of nutrient and water sources, diversity in the development of lakes around the earth and finally diversity within specific lakes. From the long list of available models I chose the model PCLake to use in my analysis because it is the most extensively used food web model applied for bifurcation analysis of shallow aquatic ecosystems. The approach has resulted in a range of critical nutrient loads for different parts of Lake Taihu. Furthermore, critical nutrient loads depend on management goals, i.e. the maximum allowable chlorophyll-a concentration. According to the model results, total nutrient loads need to be more than halved to reach chlorophyll-a concentrations of 30-40 μg.L-1 in most sections of the lake. To prevent phytoplankton blooms with 20 μg.L-1 chlorophyll-a throughout Lake Taihu, both phosphorus and nitrogen loads need a nearly 90% reduction. This range contrasts to the single point of recovery that is often found for small shallow lakes. The range in critical nutrient loads found for Lake Taihu can be interpreted as providing a path of recovery for which each step leads to water quality improvement in certain parts of the lake. To reach total recovery, nutrient reduction seems to be the most promising management option.

Super-performance in a palm species
Jansen, Merel - \ 2016
University. Promotor(en): Niels Anten; Pieter Zuidema, co-promotor(en): Frans Bongers; M. Martínez-Ramos. - Wageningen : Wageningen University - ISBN 9789462579996 - 193
chamaedorea elegans - understorey - tropical forests - spatial variation - leaves - growth - population ecology - defoliation - genetic variation - onderlaag - tropische bossen - ruimtelijke variatie - bladeren - groei - populatie-ecologie - ontbladering - genetische variatie

The world is changing rapidly due to anthropogenic disturbance. Effects include: global warming, massive pollution, a changed global nitrogen cycle, high rates of land-use change, and exotic species spread. This has a tremendous impact on both natural and agricultural systems. To understand these impacts, good understanding of ecological systems and underlying drivers is necessary. Ecological systems can be studied at different levels of aggregation. Different levels of aggregation influence each other and are also influenced by external drivers like the environment. The population level is of particular interest, because many important ecological processes occur at the population level, like evolution, extinction, and invasion. Ecologists are increasingly recognizing that population processes are strongly influenced by one level of aggregation lower, the individual level. Individual heterogeneity (i.e. differences between individuals in performance), determines many population processes including population growth rate. However, the exact relations between individual heterogeneity, the external drivers of it, and the population level are not always well understood. Furthermore, methods to analyze these relations are not always available.

Individual heterogeneity occurs at different temporal scales, ranging from short- to long-term performance differences between individuals, where short- and long-term refer to the expected lifespan of the species in question. Short-term differences between individuals are relatively easily identifiable and are common in almost all species. But long-term differences are much harder to determine especially for long-lived organisms. Long-term differences between individuals in reproduction have been identified for several animal species, and in growth for several tree species, but less is known about the existence of such differences in other life forms (e.g. palms, lianas or clonal plants). Quantifying the extent to which individuals differ is essential for understanding the influence of individual heterogeneity on population processes. Super-performing individuals (i.e. individuals that persistently grow faster and reproduce more than others), probably contribute more to the growth of the population and therefore to future generations. Future populations will, therefore, have the genetic characteristics of the super-performers. Which characteristics this will be, depends on the genetic and environmental drivers of super-performance. Full understanding of the influence of individual heterogeneity on population processes, therefore, requires knowledge of the underlying causes of individual heterogeneity.

For many species, it is known that spatial variation in environmental conditions can cause short-term performance differences between individuals, but it is often not clear if the same environmental factors that cause short-term performance differences are also the environmental factors that cause long-term performance differences. Furthermore, genetic variation is known to cause performance differences, but to what extent is not well studied in natural long-lived plant populations. Within-population genetic variation can be maintained in habitats that are characterized by strong temporal or spatial heterogeneity in environmental conditions if the performance of a genotype relative to others depends on the environment it experiences.

Super-performing individuals possibly play an important role in the resistance and resilience of populations to disturbance (i.e. maintaining and recovering population growth rate under stress), because super-performers potentially contribute more to the recovery of the population. However, this depends on the relative tolerance to disturbance of super-performers compared to under-performers. A positive relation between performance and tolerance would make super-performers more important, while a negative relation would make them less important. Many types of disturbances entail leaf loss and tolerance to leaf loss is associated with performance being larger than what one would assume based on the amount of leaf area loss. Tolerance can be achieved by compensating for leaf loss in terms of growth rate, which entails either allocating more new assimilates to leaves, allocating new assimilates more efficiently to leaf area (i.e. by increasing specific leaf area), or growing faster with existing leaf area (i.e. by increasing net assimilation rate). Genetic variation in tolerance and compensatory responses would allow populations to adapt to changes in disturbance events that entail leaf loss.

Individual heterogeneity could also have implications for management. Plant and animal populations are managed at many different levels ranging from harvest from natural populations to modern agricultural practices. When harvesting from natural populations, it might be beneficial to spare the individuals that are most important for future production. Individuals could be spared, either because they contribute most to population growth, because they are tolerant to harvesting (which is relevant when only part of a plant is harvested), or when they start producing less or lower quality product. The productivity of natural populations could also be increased by actively promoting those environmental conditions and genotypes that allow for high productivity, which is the basis of agriculture and common practice in forest management. To determine how this can best be done, knowledge of the causes of individual heterogeneity is necessary.

The general aim of this thesis is to identify and quantify the mechanisms that determine individual heterogeneity and to determine how this heterogeneity, in turn, affects population level processes. This aim was divided into four main questions that I addressed: (1) To what extent do individuals differ in performance? (2) What causes individual heterogeneity in performance? (3) What are the demographic consequences of individual heterogeneity? (4) Can individual differences be used to improve the management of populations? To answer these questions, we used the tropical forest understorey palm Chamaedorea elegans as a study system, of which the leaves are an important non-timber forest product that is being used in the floral industry worldwide. We collected demographic data, measured spatial variation in environmental conditions, and applied a defoliation treatment to simulate leaf harvesting, in a natural population in Chiapas, Mexico. Furthermore, we grew seedlings from different mothers from our study population in the greenhouses of Wageningen University, where we also applied a defoliation treatment.

In Chapter 2 we quantified the extent to which individuals differ in long-term growth rate, and analyzed the importance of fast growers for population growth. We reconstructed growth histories from internodes and showed that growth differences between individuals are very large and persistent in our study population. This led to large variation in life growth trajectories, with individuals of the same age varying strongly in size. This shows that not only in canopy trees but also in species in the light limited understorey growth differences can be very large. Past growth rate was found to be a very good predictor of current performance (i.e. growth and reproduction). Using an Integral Projection Model (i.e. a type of demographic model) that was based on size and past growth rate, we showed that fast-growing individuals are much more important for population growth than others: the 50% fastest growing individuals contributed almost two times as much to population growth as the 50% slowest growing individuals.

In Chapter 3 we analyzed the extent to which observed long-term growth differences can be caused by environmental heterogeneity. Short-term variation in performance was mainly driven by light availability, while soil variables and leaf damage had smaller effects, and spatial heterogeneity in light availability and soil pH were autocorrelated over time. Using individual-based simulation models, we analyzed the extent to which spatial environmental heterogeneity could explain observed long-term variation in growth, and showed that this could largely be explained if the temporal persistence of light availability and soil pH was taken into account. We also estimated long-term inter-individual variation in reproduction to be very large. We further analyzed the importance of temporal persistence in environmental variation for long-term performance differences, by analyzing the whole range of values of environmental persistence, and the strength of the effect of the environmental heterogeneity on short-term performance. We showed that long-term performance differences become large when either the strength of the effect of the environmental factor on short-term performance is large, or when the spatial variation in the environmental factor is persistent over time. This shows that an environmental factor that in a short-term study might have been dismissed as unimportant for long-term performance variation, might, in reality, contribute strongly.

In Chapter 4 we tested for genetic variation in growth potential, tolerance to leaf loss, compensatory growth responses, and if growth potential and tolerance were genetically correlated in our study population. We quantified compensatory responses with an iterative growth model that takes into account the timing of leaf loss. Genetic variation in growth potential was large, and plants compensated strongly for leaf loss, but genetic variation in tolerance and compensatory growth responses was very limited. Growth performances in defoliated and undefoliated conditions were positively genetically correlated (i.e. the same genotypes perform relatively well compared to others, both with and without the stress of leaf loss). The high genetic variation in growth potential and the positive correlation between treatments suggests that the existence of super-performing individuals in our study population likely has (at least in part) a genetic basis. These super-performing individuals, that grow fast even under the stress of leaf loss, possibly contribute disproportionately to population resistance and resilience to disturbance. The low genetic variation in tolerance and compensatory responses, however, suggests that populations might have limited ability to adapt to changes in disturbance regimes that entail increases in leaf loss. Furthermore, the high genetic variation in growth potential could potentially be used in management practices like enrichment planting.

In Chapter 5 we explore the potential of using individual heterogeneity to design smarter harvest schemes, by sparing individuals that contribute most to future productivity. We tested if fast and slow growers, and small and large individuals, responded differently to leaf loss in terms of vital rates, but found only very limited evidence for this. Using Integral Projection Models that were based on stem length and past growth rate, we simulated leaf harvest over a period of 20 years, in several scenarios of sparing individuals, which we compared to “Business as usual” (i.e. no individuals being spared, BAU). Sparing individuals that are most important for population growth, was beneficial for population size (and could, therefore, reduce extinction risk), increased annual leaf harvest at the end of the simulation period, but cumulated leaf harvest over 20 years was much lower compared to BAU. Sparing individuals that produced leaves of non-commercial size (i.e. <25cm), therefore allowing them to recover, also resulted in a lower total leaf harvest over 20 years. However, a much higher harvest (a three-fold increase) was found when only leaves of commercial size were considered. These results show that it is possible to increase yield quality and sustainability (in terms of population size) of harvesting practices, by making use of individual heterogeneity. The analytical and modeling methods that we present are applicable to any natural system from which either whole individuals, or parts of individuals, are harvested, and provide an extra tool that could be considered by managers and harvest practitioners to optimize harvest practices.

In conclusion, in this thesis, I showed that in a long-lived understorey palm growth differences are very large and persistent (Chapter 2) and that it is likely that long-term differences in reproduction are also very large (Chapter 3). I also showed that spatial heterogeneity in environmental conditions can to a large extent explain these differences and that when evaluating the environmental drivers of individual heterogeneity, it is important to take the persistence of spatial variation into account (Chapter 3). Individual heterogeneity also is partly genetically determined. I showed that genetic variation in growth potential to be large (Chapter 4), and that fast growers keep on growing fast under the stress of leaf loss (Chapters 4,5). Therefore it is likely that genetic variation contributes to long-term differences between individuals. Genetic variation for tolerance and compensatory responses was estimated to be low (Chapter 4), suggesting that the adaptive potential of our study population to changes in disturbance events that entail leaf loss might be low. I also showed that super-performing individuals are much more important for the growth of the population (Chapter 2) and that individuals that are important for future production could be used to improve the management of natural populations (Chapter 5).

This study provides improved insight into the extent of individual heterogeneity in a long-lived plant species and its environmental and genetic drivers, and clearly shows the importance of individual heterogeneity and its drivers for population processes and management practices. It also presents methods on how persistent performance differences between individuals can be incorporated into demographic tools, how these can be used to analyze individual contributions to population dynamics, to extrapolate short-term to long–term environmental effects, and to analyze smart harvesting scenarios that take differences between individuals into account. These results indicate that individual heterogeneity, underlying environmental and genetic drivers, and population processes are all related. Therefore, when evaluating the effect of environmental change on population processes, and in the design of management schemes, it is important to keep these relations in mind. The methodological tools that we presented provide a means of doing this.

Sleutels tot herstel van hoogveen
Limpens, J. ; Duinen, G.A. van; Schouten, M.G.C. ; Tomassen, H. - \ 2016
Landschap : tijdschrift voor Landschapsecologie en Milieukunde 33 (2016)2. - ISSN 0169-6300 - p. 82 - 91.
natuurbeheer - hoogveengronden - hoogveengebieden - ecologisch herstel - biodiversiteit - toegepast onderzoek - hydrologische factoren - ruimtelijke variatie - sphagnum - bodems van waterrijke gebieden - waterstand - nature management - bog soils - moorlands - ecological restoration - biodiversity - applied research - hydrological factors - spatial variation - wetland soils - water level
Hoogvenen herbergen een unieke biodiversiteit, variërend van insectenetende zonnedauw, kleurrijke veenmossen tot broedende kraanvogels. Genoeg reden dus om hoogvenen te beschermen en te herstellen. Dankzij de nauwe samenwerking tussen beheerders en onderzoekers en de daaruit resulterende kennisontwikkeling is herstel van levend hoogveen in Nederland niet langer een droom. In dit artikel geven we een overzicht van de hoogtepunten van 18 jaar OBN-onderzoek en sluiten af met een kijkje naar de toekomst.
Temporal and spatial variability of urban heat island and thermal comfort within the Rotterdam agglomeration
Hove, B. van; Jacobs, C.M.J. ; Heusinkveld, B.G. ; Elbers, J.A. ; Driel, B.L. van; Holtslag, A.A.M. - \ 2015
Building and Environment 83 (2015). - ISSN 0360-1323 - p. 91 - 103.
klimaatverandering - temperatuur - perceptie - stedelijke gebieden - ruimtelijke variatie - variatie in de tijd - rotterdam - climatic change - temperature - perception - urban areas - spatial variation - temporal variation - air-temperature - street geometry - canyon geometry - climate zones - land-use - environment - areas - radiation - impact - fluxes
This paper reports on temporal and spatial variability of local climate and outdoor human thermal comfort within the Rotterdam agglomeration. We analyse three years of meteorological observations (2010–2012) from a monitoring network. Focus is on the atmospheric urban heat island (UHI); the difference in air temperature between urban areas and rural surroundings. In addition, we calculate the Physiologically Equivalent Temperature (PET) which is a measure of thermal comfort. Subsequently, we determine the dependency of intra-urban variability in local climate and PET on urban land-use and geometric characteristics. During a large part of the year, UHI-intensities in densely built areas can be considerable, under calm and clear (cloudless) weather conditions. The highest maximum UHI-values are found in summer, with 95-percentile values ranging from 4.3 K to more than 8 K, depending on the location. In winter, UHI-intensities are generally lower. Intra-urban variability in maximum UHI-intensity is considerable, indicating that local features have an important influence. It is found to be significantly related to building, impervious and green surface fractions, respectively, as well as to mean building height. In summer, urban areas show a larger number of discomfort hours (PET > 23 °C) compared to the reference rural area. Our results indicate that this is mainly related to the much lower wind velocities in urban areas. Also intra-urban variability in thermal comfort during daytime appears to be mainly related to differences in wind velocity. After sunset, the UHI effect plays a more prominent role and hence thermal comfort is more related with urban characteristics.
The influence of spatiotemporal variability and adaptations to hypoxia on empirical relationships between soil acidity and vegetation
Cirkel, D.G. ; Witte, J.P.M. ; Bodegom, P.M. van; Nijp, J.J. ; Zee, S.E.A.T.M. van der - \ 2014
Ecohydrology 7 (2014)1. - ISSN 1936-0584 - p. 21 - 32.
bodemchemie - bodemaciditeit - vegetatietypen - bodem-plant relaties - soortensamenstelling - plantenfysiologie - rizosfeer - wetlands - heterogeniteit - ecohydrologie - ruimtelijke variatie - soil chemistry - soil acidity - vegetation types - soil plant relationships - species composition - plant physiology - rhizosphere - heterogeneity - ecohydrology - spatial variation - ellenberg indicator values - field-measurements - plant ecology - ph changes - iron - regression - diversity - diffusion - oxidation
Soil acidity is well known to affect the species composition of natural vegetation. The physiological adaptations of plants to soil acidity and related toxicity effects and nutrient deficiencies are, however, complex, manifold and hard to measure. Therefore, generally applicable quantifications of mechanistic plant responses to soil acidity are still not available. An alternative is the semi-quantitative and integrated response variable ‘indicator value for soil acidity’ (Rm). Although relationships between measured soil pH and Rm from various studies are usually strong, they often show systematic bias and still contain high residual variances. On the basis of a well-documented national dataset consisting of 91 vegetation plots and a dataset with detailed, within-plot, pH measurements taken at three periods during the growing season, it is shown that strong spatiotemporal variation of soil pH can be a critical source of systematic errors and statistical noise. The larger part of variation, however, could be explained by the moisture status of plots. For instance, Spearman's rho decreased from 93% for dry plots and 87% for moist plots to 59% for wet plots. The loss of relation between soil pH and Rm in the moderately acid to alkaline range at increasingly wetter plots is probably due to the establishment of aerenchyma-containing species, which are able to control their rhizosphere acidity. Adaptation to one site factor (oxygen deficit) apparently may induce indifference for other environmental factors (Fe2+, soil pH). For predictions of vegetation response to soil acidity, it is thus important to take the wetness of plots into account
Functional classification of spatially heterogeneous environments: the Land Cover Mosaic approach in remote sensing
Obbink, M.H. - \ 2011
University. Promotor(en): M. Molenaar, co-promotor(en): Jan Clevers. - [S.l.] : S.n. - ISBN 9789085859956 - 304
remote sensing - heterogeniteit - tropische regenbossen - ruimtelijke variatie - classificatie - landschapsecologie - besluitvorming - heterogeneity - tropical rain forests - spatial variation - classification - landscape ecology - decision making

Tropical rainforest areas are difficult to classify in the digital analysis of remote sensing data because of spatial heterogeneity. Often many technical solutions are adopted to reduce the ‘problem’ of spatial heterogeneity. This thesis describes theory and methods that now use this heterogeneity during the digital image classification. With spatial heterogeneity, spatial aggregation levels such as patches,patch-mosaics and landscapes can be distinguished. Consequently, vegetation patterns can be related to functional management units at different decision-levels. The developed theory and methods thus save two birds with one stone: (a) the classification is completely digitally, and (b) the classification provides information on deforestation that meets the needs of decision-makers. This thesis further recommends approaching all land cover classifications from a heterogeneous perspective for understanding and controlling environmental processes on a global level. This can enhance a sustainable development of tropical rainforest areas for the benefit of future generations.

Spatiotemporal variability in soil acidity, the role of micro topography and plant-soil interactions in wet meadow habitats
Cirkel, D.G. ; Witte, J.P.M. ; Zee, S.E.A.T.M. van der - \ 2010
bodemaciditeit - bodem-plant relaties - ruimtelijke variatie - veenweiden - ecohydrologie - soil acidity - soil plant relationships - spatial variation - peat grasslands - ecohydrology
Poster presentation for the Latsis 2010 International Symposium on Ecohydrology, Lausanne, Switserland.
Observing temporal and spatial variability of forage quality
Knox, N. - \ 2010
University of Twente. Promotor(en): Andrew Skidmore; Herbert Prins. - Enschede : ITC - ISBN 9789061642947 - 187
ruwvoer (forage) - voederplanten - natuurlijke graslanden - savannen - variatie in de tijd - ruimtelijke variatie - zuid-afrika - voederkwaliteit - forage - fodder plants - natural grasslands - savannas - temporal variation - spatial variation - south africa - forage quality
Tick tactics : interactions between habitat characteristics, hosts and microorganisms in relation to the biology of the sheep tick Ixodes ricinus
Gassner, F. - \ 2010
University. Promotor(en): Willem Takken; Marcel Dicke, co-promotor(en): Leo van Overbeek. - [S.l.] : S.n. - ISBN 9789085858058 - 162
ixodes ricinus - ziekten overgebracht door teken - metastigmata - borrelia burgdorferi - gastheer parasiet relaties - habitats - distributie - ruimtelijke variatie - variatie in de tijd - nederland - tickborne diseases - host parasite relationships - distribution - spatial variation - temporal variation - netherlands
Latitudinal patterns of magnitude and interannual variability in net ecosystem exchange regulated by biological and environmental variables
Yuan, W.P. ; Luo, Y.Q. ; Richardson, A.D. ; Oren, R. ; Luyssaert, S. ; Janssens, I.A. ; Ceulemans, R. ; Zhou, X.H. ; Grunwald, T. ; Aubinet, M. ; Berhofer, C. ; Baldocchi, D.D. ; Chen, J.Q. ; Dunn, A.L. ; Deforest, J.L. ; Dragoni, D. ; Goldstein, A.H. ; Moors, E.J. ; Munger, J.W. ; Monson, R.K. ; Suyker, A.E. ; Star, G. ; Scott, R.L. ; Tenhunen, J. ; Verma, S.B. ; Vesala, T. ; Wofsy, S. - \ 2009
Global Change Biology 15 (2009)12. - ISSN 1354-1013 - p. 2905 - 2920.
netto ecosysteem uitwisseling - kooldioxide - eddy-covariantie - patronen - ruimtelijke variatie - variatie in de tijd - net ecosystem exchange - carbon dioxide - eddy covariance - patterns - spatial variation - temporal variation - water-vapor exchange - northern temperate grassland - native tallgrass prairie - carbon-dioxide exchange - long-term measurements - plant functional-type - eddy covariance data - deciduous forest - european forests - co2 exchange
Over the last two and half decades, strong evidence showed that the terrestrial ecosystems are acting as a net sink for atmospheric carbon. However the spatial and temporal patterns of variation in the sink are not well known. In this study, we examined latitudinal patterns of interannual variability (IAV) in net ecosystem exchange (NEE) of CO2 based on 163 site-years of eddy covariance data, from 39 northern-hemisphere research sites located at latitudes ranging from ~29°N to ~64°N. We computed the standard deviation of annual NEE integrals at individual sites to represent absolute interannual variability (AIAV), and the corresponding coefficient of variation as a measure of relative interannual variability (RIAV). Our results showed decreased trends of annual NEE with increasing latitude for both deciduous broadleaf forests and evergreen needleleaf forests. Gross primary production (GPP) explained a significant proportion of the spatial variation of NEE across evergreen needleleaf forests, whereas, across deciduous broadleaf forests, it is ecosystem respiration (Re). In addition, AIAV in GPP and Re increased significantly with latitude in deciduous broadleaf forests, but AIAV in GPP decreased significantly with latitude in evergreen needleleaf forests. Furthermore, RIAV in NEE, GPP, and Re appeared to increase significantly with latitude in deciduous broadleaf forests, but not in evergreen needleleaf forests. Correlation analyses showed air temperature was the primary environmental factor that determined RIAV of NEE in deciduous broadleaf forest across the North American sites, and none of the chosen climatic factors could explain RIAV of NEE in evergreen needleleaf forests. Mean annual NEE significantly increased with latitude in grasslands. Precipitation was dominant environmental factor for the spatial variation of magnitude and IAV in GPP and Re in grasslands.
Effects of spatial variation in land cover on N2O emission of Dutch fen meadow systems
Nol, L. ; Verburg, P.H. ; Heuvelink, G.B.M. - \ 2008
ruimtelijke variatie - grondbeheer - emissie - stikstof - grondbedekking - aardoppervlak - spatial variation - land management - emission - nitrogen - ground cover - land surface
Poster on effects of spatial variation in land cover on N2O emission of Dutch fen meadow systems
Drainage induced variability of N2O emission from grassland on peat soil
Beek, C.L. ; Groenigen, J.W. van; Pleijter, M. ; Kuikman, P.J. - \ 2008
emissie - distikstofmonoxide - veengronden - toevloei naar drains - ruimtelijke variatie - graslanden - emission - nitrous oxide - peat soils - flow to drains - spatial variation - grasslands
Approximately 42% of the Dutch agricultural land is drained using tile drains. Of all Dutch soil types peat soils are responsible for the highest emission of nitrous oxide per unit of surface for agricultural land. The emission of nitrous oxide is characterized by its high spatial variability, to which the presence of tile drains may contribute. The objective of this study was to quantify the spatial variability due to drainage of peat soil on grassland
Temporal and spatial changes in land use patterns and biodiversity in relation to farm productivity at multiple scales in Tigray, Ethiopia
Hadgu Meles, K. - \ 2008
University. Promotor(en): Ariena van Bruggen, co-promotor(en): Walter Rossing; Lammert Kooistra. - [S.l.] : S.n. - ISBN 9789085852124 - 174
landgebruik - biodiversiteit - duurzaamheid (sustainability) - ruimtelijke variatie - faidherbia albida - hordeum vulgare - gerst - gewasopbrengst - landbouwproductie - grondproductiviteit - ethiopië - agrobiodiversiteit - landgebruiksmonitoring - duurzame landbouw - land use - biodiversity - sustainability - spatial variation - barley - crop yield - agricultural production - land productivity - ethiopia - agro-biodiversity - land use monitoring - sustainable agriculture
Loss of biodiversity, including agro-biodiversity affects smallholders in dry-land regions by decreasing the buffering capacity of the agro-ecosystem and increasing proneness to yield variability including crop failure due to weather extremes. Loss of biodiversity is associated with land use/land cover (LULC) changes that are related to a range of biophysical and socio-economic drivers. This thesis is focused on the Tigray region in northern Ethiopia which has experienced severe loss of biodiversity over the last decades at the regional scale, while loss of genetic variation of crops at the farm and field scale are ongoing as a result of agricultural technology adoption processes. The overall goal of this thesis research was to identify and analyse factors affecting loss of agro-biodiversity in Tigray, Ethiopia, and relate agro-biodiversity loss to LULC changes, soil erosion, farming practices and agricultural productivity. A multi-scale approach was adopted. At the regional scale, LULC changes over the last decades were investigated using a time-series of remotely sensed data to assess changes in biodiversity. At the farm scale, changes in farming practices and land use between 2000 and 2005 were described along with their effects on agro-biodiversity. These changes were related to biophysical and socio-economic drivers. Finally, at the field scale, the consequences of the presence of Acacia albida trees for productivity were assessed. A survey among 151 farms in Tigray indicated that higher numbers of species of trees and shrubs, along with cultivation of land races was associated with traditional farming practices of smallholders in 2000 and 2005. Classified maps from remotely sensed data indicated that significant changes in LULC were accompanied by loss of biodiversity and intensification of agricultural production. At the same time, overall caloric yields were highest and soil erosion lowest in sparsely cultivated areas with high biodiversity, where traditional farming practices still dominate. At the farm scale, it was shown that A. albida trees contribute significantly to soil fertility and barley yield. Results of this project may assist policy development on agro-biodiversity restoration by providing information on long-term historical trends, insight into their drivers, and consequences for food security among resource poor smallholders in the region.
Variation in space and time of water flow and solute transport in heterogeneous soils and aquifers : a new multi-compartment percolation sampler and a new parameterization of the spatio-temporal solute distribution
Bloem, E. - \ 2008
University. Promotor(en): Reinder Feddes, co-promotor(en): G.H. de Rooij. - S.l. : S.n. - ISBN 9789085049227 - 153
grondwaterstroming - opgeloste stof - transportprocessen - watervoerende lagen - variatie in de tijd - bemonsteren - distributie - grondwaterverontreiniging - ruimtelijke variatie - groundwater flow - solutes - transport processes - aquifers - temporal variation - sampling - distribution - groundwater pollution - spatial variation
Het experimentele en theoretische onderzoek gepresenteerd in dit proefschrift heeft geleid tot een verbetering van de mogelijkheden om stoffentransport in de ondergrond beneden een onverzadigde bodem te observeren. De lange termijn prestaties van de nieuwe multi-compartement samplers onder de ruwe omstandigheden van het open veld waren overtuigend. De samplers bleken geschikt voor een grotere verscheidenheid aan toepassingen
Risicogebieden voor verspreiding van Klassieke Varkenspest bij verschillende interventiestrategieën
Gies, T.J.A. ; Boender, G.J. ; Baveco, J.M. ; Nodelijk, G. - \ 2008
varkenspest - varkensziekten - risicoschatting - diergezondheid - ziektedistributie - ruimtelijke variatie - klassieke varkenspest - risicobeheersing - swine fever - swine diseases - risk assessment - animal health - disease distribution - spatial variation - classical swine fever - risk management
Binnen het onderzoeksprogramma 428 "Risicomanagement diergezondheid en voedselveiligheid" van het Ministerie van Landbouw, Natuur en Voedselkwaliteit is onderzoek gedaan naar de verspreidingsrisico's na uitbraak van varkenspest en het effect van verschillende interventiestrategieën op dit risico. In deze poster wordt aandacht besteed aan methodiek, risicogebieden en toepassingsmogelijkheden
Spatial model reduction for transport phenomena in environmental and agricultural engineering
Dirkse, M.H. - \ 2008
University. Promotor(en): Gerard Bot, co-promotor(en): Wilko van Loon; Hans Stigter. - [S.l.] : S.n. - ISBN 9789085048633 - 143
transportprocessen - warmteoverdracht - massaoverdracht - simulatiemodellen - convectie - tweedimensionale stroming - warmtewisselaars - ruimtelijke verdeling - ruimtelijke variatie - systemen - systeemanalyse - elektrodialyse - computationele vloeistofdynamica - modelleren - procesbewaking - transport processes - heat transfer - mass transfer - simulation models - convection - two dimensional flow - heat exchangers - spatial distribution - spatial variation - systems - systems analysis - electrodialysis - computational fluid dynamics - modeling - process control
Tijdens het ontwerpen van landbouwkundige en industriële installaties is het belangrijk om het energieverbruik van tevoren in te schatten. Simpele berekeningen volstaan om het energieverbruik globaal te schatten, maar vaak kan het energieverbruik significant worden verminderd door de vorm van het systeem slim te kiezen. De invloed van deze verbeteringen kan niet met simpele berekeningen worden voorspeld. Deze promotie gaat over een nieuwe methode om de invloed van de geometrie te analyseren. De methode is gebaseerd op toepassing van complexe functietheorie op stromingsproblemen; de zognaamde potentiaaltheorie. Als voorbeelden worden een warmtewisselaar en een omgekeerde elektrodialyse installatie onderzocht. Als de methode verder wordt uitontwikkeld, dan kan dit in de toekomst leiden tot besparingen van tijd en geld tijdens de ontwerpfase van technische installaties.
De voedselsituatie voor gruttokuikens bij agrarisch mozaïekbeheer
Kleijn, D. ; Dimmers, W.J. ; Kats, R.J.M. van; Melman, T.C.P. ; Schekkerman, H. - \ 2007
Wageningen : Alterra (Alterra-rapport 1487) - 50
limosa limosa - voedering - natuurbescherming - agrarische bedrijfsvoering - graslandbeheer - overleving - ruimtelijke variatie - nederland - voedingsecologie - weidevogels - agrarisch natuurbeheer - feeding - nature conservation - farm management - grassland management - survival - spatial variation - netherlands - feeding ecology - grassland birds - agri-environment schemes
Mozaiekbeheer blijkt niet te leiden tot de gewenste verhoging van overleving bij grutto's. In dit rapport is onderzocht wat de vegetatiesamenstelling van de graslanden is en wat het aanbod aan ongewervelden voor weidevogels in die percelen is. Het blijkt dat kruidenrijke, schrale percelen een goede vegetatiestructuur gedurende de gehele kuikenperiode hebben; terwijl de ongewervelden in mei hoger is dan in juni
Spatial analysis of weed patterns
Heijting, S. - \ 2007
University. Promotor(en): Martin Kropff; A. Stein, co-promotor(en): Wopke van der Werf. - [S.l.] : S.n. - ISBN 9789085047919 - 146
onkruiden - onkruidbestrijding - onkruidbiologie - ruimtelijke variatie - statistische analyse - ruimtelijke verdeling - geostatistiek - ruimtelijke statistiek - weeds - weed control - weed biology - spatial variation - statistical analysis - spatial distribution - geostatistics - spatial statistics
Keywords: Spatial analysis, weed patterns, Mead’s test, space-time correlograms, 2-D correlograms, dispersal, Generalized Linear Models, heterogeneity, soil, Taylor’s power law. Weeds in agriculture occur in patches. This thesis is a contribution to the characterization of this patchiness, to its analysis, and to its prediction, and some of its results may be useful for weed management. Spatial patterns of six weed species monitored in contiguous quadrats are characterized, using Mead’s test. Five of the six analysed weed species showed aggregation at several levels of scale. The only wind dispersing species, Taraxacum officinale was random at all scales. Next, 2-D correlograms were used to analyse spatio-temporal behaviour of weed patterns for 15 weed species groups throughout three years. Chenopodium album, C. polyspermum, E. crus-galli and S. nigrum were strongly aggregated and also exhibited the largest incidence and highest maximum weed density of the species studied. 2-D correlograms showed that patterns of C. polyspermum and S. nigrum were stable in location. Patches of one species, E. crus-galli appeared to shift from year to year. The four patchy weed species, C. album, C. polyspermum, E. crus-galli and S. nigrum, showed consistent relations of moderate strength with soil variables (pH, texture fraction or organic matter) over the three years of study using Generalized Linear Models with a Poisson log link. Models with spatially uncorrelated and spatially correlated error terms were compared, using Taylor’s power law (TPL) as a link function, resulting in modest decreases in model significance when the spatial correlation in errors was accounted for, and in a few cases, there were big differences in model significance. Spatial correlation remained in the residuals of the regression, demonstrating that factors other than the selected soil variables also contributed to the spatial correlation in the weeds. Dispersal of weed seeds in fields by harvest and rigid-tine cultivator was studied in continuous maize using a range of plant species as model weeds. The rigid-tine cultivator significantly contributed to the dispersal in the driving direction, most likely by dragging plant material with seeds through the field. Irregularities were found in the tail of the dispersal kernels, probably as a result of deposition of plant debris in the headlands by machinery. Taylor’s power law was used to predict the weed free fraction in the field using spatially implicit weed count data. The general model gave accurate predictions for most weed species, but for some, e.g. E. crus-galli, a species specific model was required to achieve adequate accuracy.
Moving to eat : animal foraging movements in a heterogeneous environment
Hengeveld, G.M. - \ 2007
University. Promotor(en): Herbert Prins, co-promotor(en): Frank van Langevelde. - [S.l.] : S.n. - ISBN 9789085047186 - 112
foerageren - heterogeniteit - voedingsgedrag - ruimtelijke variatie - voedselopname - beweging - dieren - zoekgedrag - foraging - heterogeneity - feeding behaviour - spatial variation - food intake - movement - animals - searching behaviour
Animals moving from one place to another transport seeds, parasites, genes and grazing pressure. Insight in the spatial linkage between ecological processes can be gained from understanding the driving forces behind animal movement patterns. From this understanding predictions can be made about which patterns are most likely to be encountered. This thesis addresses the role of foraging in animal movement. Central is the study of the searching efficiency and diffusion of Lévy random searches, both through computer simulations and experiments with goats and ring doves. These computer simulations show that the interactions with targets are crucial in optimising Lévy random searches. Additionally, predictions are made about which foraging decisions animals should make in order to optimise their intake of several nutrients. Finally it is shown how different movement patterns can be incorporated in mean-field approaches of ecology.
Spatial matters : how spatial patterns & processes affect savanna dynamics
Groen, T.A. - \ 2007
University. Promotor(en): Herbert Prins, co-promotor(en): Frank van Langevelde. - [S.l.] : S.n. - ISBN 9789085046905 - 151
savannebossen - savannen - ruimtelijke verdeling - ruimtelijke variatie - patronen - impact - herbivoren - bosbranden - savanna woodlands - savannas - spatial distribution - spatial variation - patterns - herbivores - forest fires
Dit proefschrift laat zien dat vuur en herbivorie in staat zijn om ruimtelijke patronen te creëren en in stand te houden. Bovendien laat het zien dat het negatieve effect van vuur op bomen minder wordt als bomen in groepen in de ruimte zijn georganiseerd. Ruimtelijk heterogene ecosystemen blijken minder gevoelig te zijn voor plotselinge verschuivingen, dan homogene gebieden. Echter, zodra een savanne eenmaal geheel verbost is, zal het niet gemakkelijk terugkeren naar zijn oorspronkelijke staat
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