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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    Prof. Liesje Mommer over groei en overlevingskansen bij planten
    Mommer, L. - \ 2016
    Wageningen UR
    biodiversiteit - plantenecologie - landbouwkundig onderzoek - plantenontwikkeling - openbare redes - microbiële interacties - grondvegetatie - wortels - planteninteractie - biodiversity - plant ecology - agricultural research - plant development - public speeches - microbial interactions - ground vegetation - roots - plant interaction
    Planten jutten elkaar op. Verschillende gewassen die samen een vegetatie vormen, groeien beter dan wanneer er maar één soort groeit. Maar hoe werkt dat? Welke processen onder de grond zorgen ervoor dat deze gewassen samen beter groeien? Prof. Liesje Mommer licht een tip van de sluier op tijdens haar inaugurele rede als persoonlijk hoogleraar bij de leerstoelgroep Plantenecologie en natuurbeheer aan Wageningen
    Liesje Mommer schijnt licht op de wortelwereld
    Kleis, R. ; Mommer, L. - \ 2015
    Resource: weekblad voor Wageningen UR 10 (2015)4. - ISSN 1874-3625 - p. 9 - 9.
    plantenecologie - wortelsystemen - biodiversiteit - soortendiversiteit - stofwisselingsstoornissen - gewasbescherming - plantenziekteverwekkende schimmels - plant ecology - root systems - biodiversity - species diversity - metabolic disorders - plant protection - plant pathogenic fungi
    Nieuwe persoonlijk hoogleraar Plantenecologie. Hoe meer soorten, hoe minder schimmels.
    Ecology of lianas
    Schnitzer, S.A. ; Bongers, F. ; Burnham, R.J. ; Putz, F.E. - \ 2015
    Oxford : Wiley-Blackwell - ISBN 9781118392492 - 504
    klimplanten - plantenecologie - plantenanatomie - plantenfysiologie - evolutie - tropische bossen - bossen - climbing plants - plant ecology - plant anatomy - plant physiology - evolution - tropical forests - forests
    A liana is a long-stemmed, woody vine that is rooted in the soil at ground level and uses trees to climb up to the canopy to get access to well-lit areas of the forest. The main goal of this book is to present the current status of liana ecology in tropical and temperate forests. In essence, it is a forum to summarize and synthesize the most recent research in liana ecology and to address how this research fits into the broader field of ecology.
    Surviving and growing amidst others : the effect of environmental factors on germination and establishment of savanna trees
    Moribe Barbosa, E.R. - \ 2013
    Wageningen University. Promotor(en): Herbert Prins; Steven Bie, co-promotor(en): Frank van Langevelde. - S.l. : s.n. - ISBN 9789461734655 - 125
    bomen - savannen - kieming - milieufactoren - vestiging - concurrentie tussen planten - zaailingen - plantenontwikkeling - plantenecologie - trees - savannas - germination - environmental factors - establishment - plant competition - seedlings - plant development - plant ecology

    Savanna ecosystems are characterized by a continuous grass layer intermixed with a discontinuous layer of trees and shrubs. A complex set of environmental drivers, such as water, soil nutrients, solar radiance, fire and herbivory, determines vegetation structure and composition in savannas.Such environmental drivers are expected to be strongly affected by future global climatic and land-use changes, potentially modifying savanna vegetation, and consequently savanna fauna. The ability to predict changes in plant community composition is therefore importantfor management and conservation of savannas. However, the mechanisms controlling plant establishment and growth in savannas are still unclear. Germination and seedling establishment are critical recruitment stages in the life cycle of plants and can influence plant community composition. A better understand of the factors influencing plant species recruitment and their ecology is needed. This thesis focuses on seedling recruitment of several savanna tree species.

    Water stress is probably the single greatest constraint to tree seedling survival in savanna systems: tree seedling recruitment and survival are hypothesized to be limited by soil moisture availability. Shade by established adult trees may facilitate tree seedling recruitment by maintaining high soil moisture availability. Chapter 2 deals with germination and early seedling establishment of several tree species. I expected that tree species would germinate and establish best under high moisture conditions (high water and shade), while under stress conditions (i.e. low soil moisture due to low water supply and full sun, and in the presence of grasses) plants would suffer. The observed variability of seedling performance among the tree species under stress conditions may be explained by differences in functional traits. Higher soil moisture mostly benefited germination of species with seeds with high calcium concentration and low water content. On the other hand, low soil moisture conditions benefited germination of tree species with seeds with higher magnesium and phosphorus concentration and water content. Furthermore, under low soil moisture availability, grass presence facilitated germination of most tree species but its effect on early survival (positive or negative) differed among species. The findings of this chapter confirm a large difference in the tree species responses to environmental variation during early recruitment, which potentially affect theplant community composition and dynamics under different environmental conditions in savannas.Seed trait differences among the species partly contribute to explain such variability. Therefore, considering inter-specific variation among tree species and information on seed traits can improve the ability to predict and manage the impacts of environment changes.

    For later stages of seedling development (up to 9 months), the effect of environmental variation (water, nutrient and light supply, as well as grass presence or absence) on survival and establishment of semi-arid savanna tree seedlings differed between species (Chapter 3). All species were expected to respond positively to higher resource availability, and negatively to the presence of grass. Indeed, the results of this chapterclearly show that grass presence strongly suppressed seedling establishment. However, recruitment strategies varied among species, particularly under high stress conditions (water stress or low light). In some of the studied tree species, light shortage (i.e., shade) reduced the negative effects of the presence of grass on growth. Furthermore, nutrient availability also reduced the negative effect of grasses, although for certain species (broad-leaf species) this effect occurred only under natural rainfall, while for others (fine-leaf species) it occurred only under regular water provision.

    Increased atmospheric nitrogen deposition, intensification of agricultural fertilizer use and large herbivore management interventions are on-going processes that increase soil nutrient levels in many savannas. As nutrient concentration in the leaves (i.e., plant quality for herbivores) also depends on soil nutrient availability, I expected in Chapter 4 that both biomass production and leaf nutrient concentration would increase with increasing soil nutrient availability. Contrary to my expectations, differences in soil nutrient levels (low vs. high) did not affect biomass production of any of the tree species, independently of water availability (uneven vs. even water supply). However, leaf nutrient content of the seedlings did differ significantly with different water and nutrient levels. Soil nutrient input increased leaf nutrient content, but only when water was applied regularly, indicating that plant nutrient uptake strongly depends on water availability. Under irregular rainfall patterns, nutrient input significantly reduced leaf quality. Given that large herbivore populations depend on plant nutrient content for their nutritional requirements, increases in nutrient deposition and rainfall levels will likely impact herbivore populations and their browsing patterns, altering the functional structure of ecosystems even if overall plant biomass remains unaffected.

    In Chapter 5, the effect of fluctuations of environmental conditions on above and belowground growth of juveniles of three savannas tree species (Acacia karroo, A. nigrescens and Colophospermum mopane) during the first 18 months was tested. While it was expected that low soil resource availability would result in high biomass allocation towards roots, experimental simulation of dry eventswithin the wet season or pulses of nutrient availability did not have a clear effect on the seedlings’ aboveground and belowground growth. Furthermore, the results of this chapter demonstrated that browsing stimulated stem regrowth and root elongation of savanna tree seedlings, suggesting that the three studied species have compensatory growth in response to frequent herbivory, quickly recovering the loss of biomass. This result puts in question the usefulness of herbivory or human land-cleaning in controlling invasive woody species in tropical grasslands and savannas.

    In conclusion, the results of this thesis demonstrated that savanna tree species are generally able to cope with differences in resource availability during seedling establishment, being mostly limited by grass competition for resource. Furthermore, this study shows that during early stages of the life-cycle, when exposed to the same environmental conditions, tree species within a plant community differ in their responses, only having advantages over other species under specific conditions.This inter-specific variation may allow tree species coexistence, explaining the diversity of plant species in savannas.

    A combination of functionally different plant traits provides a means to quantitatively predict a broad range of species assemblages in NW Europe
    Douma, J.C. ; Aerts, R. ; Witte, J.P.M. ; Bekker, R.M. ; Kunzmann, D. ; Metselaar, K. ; Bodegom, P.M. van - \ 2012
    Ecography 35 (2012)4. - ISSN 0906-7590 - p. 364 - 373.
    vegetatietypen - plantenecologie - vegetation types - plant ecology - relative growth-rate - community ecology - strategies - diversity - convergence - divergence - patterns - model - components - nitrogen
    Assembly theory predicts that filtering processes will select species by their attributes to build a community. Some filters increase functional similarity among species, while others lead to dissimilarity. Assuming converging processes to be dominant within habitats, we tested in this study whether species assemblages across a wide range of habitats can be distinguished quantitatively by their mean trait compositions. In addition, we investigated how many and which traits are needed to describe the differences between species assemblages best. The approach has been applied on a dataset that included 12 plant traits and 7644 vegetation releves covering a wide range of habitats in the Netherlands. We demonstrate that due to the dominant role of converging processes 1) the functional composition can explain up to 80% of the floristic differences between species assemblages using seven plant traits, showing that plant trait combinations provide a powerful tool for predicting the occurrence of species assemblages across different habitats; 2) to achieve a high performance, traits should be taken from different strategy components, i.e. traits that are functionally orthogonal, which does not necessarily coincide with low trait-trait correlations; 3) the different strategy components identified in this study correspond to the strategy components of some conventional plant ecological strategy schemes (PESS) schemes to describe the variation between individual species. However, some PESS merge traits into one strategy component that are shown to be functionally different when predicting species assemblages. If such PESS is used to predict assemblages, this leads to a loss in predictive capacity. Potentially, our new approach is globally applicable to quantify community assembly patterns. However this needs to be tested.
    Kroonjuwelen van de Kaap
    Sluiter, L. ; Schaminee, J.H.J. - \ 2012
    Zeist : KNVV - ISBN 9789050114301 - 191
    plantenecologie - vegetatie - natuurbescherming - biodiversiteit - plantengeografie - fijnbos (zuid afrika) - lokale geschiedenis - inheemse volkeren - flora - westkaap - zuid-afrika - plant ecology - vegetation - nature conservation - biodiversity - phytogeography - fynbos - local history - indigenous people - western cape - south africa
    'Kroonjuwelen van de Kaap' neemt de fascinerende wereld van de Kaap onder de loep. Niet alleen de biologische rijkdom van het fynbos, maar ook de geschiedenis van het gebied en zijn bewoners. Na eeuwenlang op zichzelf te hebben geleefd, in nauw samenspel met de natuur, kregen de oorspronkelijke bewoners, de Khoikhoi en de San, vanaf de zeventiende eeuw te maken met kolonialisme, en de daaruit voortgekomen apartheid. Recente ontwikkelingen, waaronder de grootschalige teelt van rooibosthee, zetten het kwetsbare gebied en haar oeroude bevolking sterk onder druk. Maar dankzij lokale initiatieven doen duurzaamheid en eerlijke handel geleidelijk hun intrede. 'Kroonjuwelen van de Kaap' is een beeldende reportage van een bijzonder gebied en de mensen die er wonen en werken. Natuurbeschermers, wetenschappers en de lokale bevolking komen aan het woord. Het eerste deel van het boek stelt de natuur centraal, het tweede deel gaat over het menselijk gebruik van het fynbos en de vragen die dit oproept.
    An ecogeographic analysis of Oryza series Sativae in Asia and the Pacific
    Banaticla-Hilario, M.C.N. - \ 2012
    Wageningen University. Promotor(en): Marc Sosef, co-promotor(en): Ronald van den Berg; K.L. McNally. - S.l. : s.n. - ISBN 9789461733788 - 237
    oryza - oryza sativa - oryza nivara - genetische bronnen van plantensoorten - plantengeografie - plantenecologie - diversiteit - in-situ conservering - plantenmorfologie - taxonomie - genetica - genenbanken - azië - oryza - oryza sativa - oryza nivara - plant genetic resources - phytogeography - plant ecology - diversity - in situ conservation - plant morphology - taxonomy - genetics - gene banks - asia

    The non-cultivated speciesof the genus Oryza can provide a genetic arsenal of useful traits for improving the widely cultivated and consumed Asian rice (O. sativa). The diversity of these valuable plant resources must be well understood to ensure their effective in- and ex-situ conservation. In this thesis, we examined the ecogeographic variations within and between the three species of Oryza series Sativae in Asia and the Pacific. We looked at species differentiation from different spatial scales by analysing sympatric accession pairs of O. meridionalis and O. rufipogon and of O. nivara and O. rufipogon.

    We conducted phenotypic analyses in Chapter 2. The strong influence of ecology on species morphology was demonstrated in the ordination and cluster analyses results where O. meridionalis and O. nivara grouped together and were separated from O. rufipogon. We detected greater differentiation of O. nivara and O. rufipogon in South Asia and positive correlations between spatial and intraspecific (interpopulation) morphological distances in continental Asia. We found significant correlations between geoclimatic factors and certain character measurements within species and observed that seedling height, culm number and diameter, leaf size, and anther length exhibit contrasting responses for O. nivara and O. rufipogon. We confirmed significant morphological differences between the three species, between the South and Southeast Asian populations of O. nivara, and between the Australasian and the non-Australasian populations of O. rufipogon and provided botanical descriptions to delineate O. meridionalis, O. nivara and O. rufipogon morphologically.

    In Chapter 3, we genotyped the same set of accessions with 29 SSR markers and applied a variety of methods for genetic diversity analysis. Based on ordination and phylogenetic results, we verified that O. meridionalis is a genetically distinct species and that O. nivara and O. rufipogon overlap genetically across their geographic distribution. However, Bayesian clustering analysis recognized local-scale species separation of O. nivara and O. rufipogon implying stronger interspecific gene flow barriers in smaller spatial units. Concurrently, AMOVA indicated that the bulk (64%) of genetic variation in Asia Pacific series Sativae can be found among accessions and the lesser portions within accessions (26%) and among species (10%). We captured contrasting intraspecific variation patterns for O. nivara and O. rufipogon where the former exhibited low diversity, high population differentiation and isolation by distance mainly in South Asia while the latter displayed high diversity, low population differentiation and isolation by distance primarily in continental Southeast Asia. We established that altitude is correlated negatively to accession diversity and positively to local-scale species differentiation. Using Bayesian inference, we identified eight genetically distinct population groups: C1) Indian and Bangladeshi O. nivara; C2) Cambodian O. nivara; C3) Southeast Asian O. rufipogon; C4) O. meridionalis; C5) Nepalese O. nivara; C6) non-Cambodian Southeast Asian O. nivara; C7) Australasian O. rufipogon; and C8) South Asian O. rufipogon. Cluster analysis grouped the aromatic and japonica cultivar groups of O. sativa with O. rufipogon in South Asia and the indica and aus groups with O. nivara from Thailand and Cambodia, respectively. O. nivara from Nepal seemed genetically isolated from the other population groups. We also detected variation patterns that agreed with the results in Chapter 1 such as the South and Southeast Asian divisions of O. nivara, the divergence of Australasian populations from the rest of O. rufipogon and the greater differentiation of O. nivara and O. rufipogon in South Asia.

    In Chapter 4, we conducted artificial crossing experiments to 15 selected parental accessions of O. meridionalis, O. nivara, and O. rufipogon and assessed the extent of several post-pollination isolating mechanisms in Oryza series Sativae. We observed reproductive incompatibility within and between the inbreeding species O. meridionalis and O. nivara and high intraspecific crossability of the outcrossing O. rufipogon where viable and non-sterile F1 hybrids were produced only by combinations with a parental distance that ranged from 1062 to 3813 kilometers. Insular Southeast Asian and/or Australasian accessions of O. rufipogon were the most reproductively successful parents. O. rufipogon exhibited significant pre-zygotic species isolation (in terms of seed set) and reduced post-zygotic isolation, and seemed symmetrically compatible with O. nivara and asymmetrically compatible with O. meridionalis. We obtained few annual hybrids with relatively high fertilities from crosses between O. rufipogon and O. nivara and numerous perennial hybrids with low fertilities from crosses between O. rufipogon and O. meridionalis. Crossability estimates did not show significant correlations with geographic distance between parents. However, we discerned reduced seed set and F1 fertility in interspecific combinations with sympatric parents compared to crosses with non-sympatric parents, indicative of reinforced species isolation in sympatry. We evaluated the F1 offspring of different cross combinations and found a mixture of intermediate and parental character traits in interspecific hybrids.

    We discussed the taxonomic implications of the research results in Chapter 5 where we specifically dealt with the opposing views of lumping or splitting of O. nivara and O. rufipogon. We concluded that these two taxadeserve to be treated as separate species based on the following biosystematic evidence obtained from the thesis: 1) ecological distinction; 2) considerable prezygotic barriers; 3) opposing patterns of gene flow and genetic variation; 4) local-scale genetic divergence and 5) enhanced reproductive barriers under sympatric conditions. We identified ecogeography as a major driving force in the diversification of Oryza series Sativae in Asia and the Pacific and suggested that ecological speciation gave rise to O. nivara and O. rufipogon. We also presented recognizable geographic races within species.

    Ultimately in Chapter 6, we emphasized the importance of our study in several aspects of rice science and identified results that agreed with prior Oryza diversity studies. At the same time, we presented previously unreported morphological and genetic variation patterns that were established in this thesis. We discussed the possible applications of the research results to wild rice conservation, covering in situ strategies as well as gene bank practices. We also highlighted the potential role of O. nivara in Asian rice domestication where it could have either directly given rise to the indica cultivar group or hybridized/introgressed with migrated japonica cultivars in India, eventually leading to the development of indica.

    Models to relate species to environment: a hierarchical statistical approac
    Jamil, T. - \ 2012
    Wageningen University. Promotor(en): Cajo ter Braak. - S.l. : s.n. - ISBN 9789461731395 - 146
    statistiek - lineaire modellen - interacties - kenmerken - bayesiaanse theorie - plantenecologie - biostatistiek - statistics - linear models - interactions - traits - bayesian theory - plant ecology - biostatistics

    In the last two decades, the interest of community ecologists in trait-based approaches has grown dramatically and these approaches have been increasingly applied to explain and predict response of species to environmental conditions. A variety of modelling techniques are available. The dominant technique is tocluster the species based on their functional traits and then summarize the response of the clusters to environmental change. In general, fitting explicit models to data is always more informative and powerful than more informal approaches. The central theme of the thesis is how to quantify the relation of traits with the environment using three data tables, data on species occurrence and abundance in sites, data on traits of species and data on the environmental characteristics of sites. In this thesis, we place the challenge of quantifying trait-environment relationships in the context of species distribution modelling, so in the context of species-environment relationships. We present a hierarchal statistical approach to species distribution modelling that efficiently utilize the trait information and that is able to automatically select the relevant traits and environmental characteristics. This model-based approach, coupled with recent statistical developments and increased computing power, opens up possibilities that were unimaginable before.

    In the present study a hierarchical statistical approach is introduced for modeling and explaining species response along environmental gradients by species traits. The model is an extension of the generalized linear model with random terms that express the between-species variation in response to the environment. This so-called generalized linear mixed model (GLMM)is derived byintegrating a two-step procedure into one. As the basic GLMM we take the random intercept and random slope model. To introduce traits, the regression parameters (intercept and slope) are made linearly dependent on the species traits. As a consequence the trait-environment relationship is represented as an interaction term in the model. The method is illustrated using the famous Dune Meadow Data using Ellenberg indicator values as species traits.

    Niche theory proclaims that species response to environmental gradients is nonlinear. Each species has preferred an environmental condition in which it can survive and reproduce optimally. Thus each species tends to be most abundant around a specific environmental optimum and the distribution of species along any environmental gradient is usually unimodal, with the maximum at some ecological optimum.For presence-absence data, the simplest unimodal (non-negative) species response curve is the Gaussian logistic response curve with three parameters that characterize the niche: optimum (niche centre), tolerance (niche width) and maximum (expected occurrence at the centre). Niches of species differ between species and species are assumed to be evolutionary adapted. It is difficult to fit the Gaussian logistic model with linear trait submodels for the parameters with the available (generalized) nonlinear mixed model software.

    We develop the trait-modulated Gaussian logistic model in which the niche parameters are made linearly dependent on species traits. The model is fitted to data in the Bayesian frameworkusing OpenBUGS (Bayesian inference Using Gibbs Sampling).A Bayesian variable selection method is used to identify which species traits and environmental variables best explain the species data through this model. We extended the approach to find the best linear combination of environmental variables.

    We explained why and when (generalized) linear mixed models can effectively analyse unimodal data and presented a graphical tool and statistical test to test for unimodality while fitting just a generalized linear mixed model without any squared or other polynomial term. A GLMM is, of course, a linear model. Despite this fact, it can be used to detect unimodality and to fit unimodal data, with the provision that the differences in niche widthsamongspecies are not too large. As graphical tool we suggested to plot the random site effects against the environmental variable. There is an indication for unimodality, when this graph shows a quadratic relationship. The efficacy of GLMM to analyse unimodal data is illustrated by comparing the GLMM approach with an explicit unimodal model approach on simulated data and real data that show unimodality.

    When a system is described by a statistical model, model complexity leads to a very large computing time and poor estimation, especially if the number of predictors is large relative to the data size. As an alternative to and improvement over stepwise methods, shrinkage methods have been proposed. One of these is the Relevance vector machine (RVM). RVM assigns individual precisions to weights of predictors which are then estimated by maximizing the marginal likelihood (Type-II ML or empirical Bayes). We also investigated the selection properties of RVM both analytically and by experiments. We found that RVM is rather tolerant for predictors to stay in the model and concluded that RVM is not a real solution in high-dimensional data problems.

    By further study the multi-trait and multi-environmental variablemodel selection method developed that used our previous study in a linear mixed model context. The method is called tiered forward selection. In the first tier, the random factors are selected, in the second, the fixed effects are selected and in the final tier non-significant terms are removed based on a modified Akaike information criterion. The linear mixed model with the tiered forward selection is compared with Type-II ML and existing methods for detecting trait-environment relationships that are not based on mixed models, namely the fourth corner method and the linear trait-environment method (LTE).

    Winterweer kan effectiviteit van KRW-maatregelen beinvloeden
    Netten, J.J.C. ; Peeters, E.T.H.M. - \ 2011
    H2O : tijdschrift voor watervoorziening en afvalwaterbehandeling 44 (2011)16. - ISSN 0166-8439 - p. 34 - 35.
    waterbeheer - klimaatverandering - seizoenen - winter - ecosystemen - kaderrichtlijn water - plantenecologie - water management - climatic change - seasons - winter - ecosystems - water framework directive - plant ecology
    Experimentele studies tonen aan dat drijvende planten meer profiteren van klimaatverandering dan submerse planten. Een analyse van langjarige (1981-2006) meetgegevens afkomstig uit sloten onderschrijft deze bevindingen: milde winters leiden tot hogere kroosbedekking in de zomer, terwijl koude winters leiden tot meer submerse planten. Daarnaast toont onze analyse aan dat overwinterings- en groeistrategie van planten, bodemsoort en de weersomstandigheden in de winter de plantenbedekking in het groeiseizoen kunnen verklaren. Analyses van langjarige meetreeksen kunnen een belangrijke bijdrage leveren aan het begrijpen van het functioneren van ecosystemen, nu en in de toekomst. Dit kan bijvoorbeeld gebruikt worden voor de planning van het uitvoeren van voorgenomen (KRW-)maatregelen.
    Recovery of rangelands : the functioning of soil seed banks in a semi-arid African savanna
    Tessema, Z.K. - \ 2011
    Wageningen University. Promotor(en): Herbert Prins, co-promotor(en): Fred de Boer; R.M.T. Baars. - [S.l.] : S.n. - ISBN 9789085859987 - 198
    zaadbanken - zaden - bodem - savannen - vegetatie - begrazing - kieming - graszaden - semi-aride klimaat - semi-aride klimaatzones - plantenecologie - ecologie - afrika - seed banks - seeds - soil - savannas - vegetation - grazing - germination - grass seeds - semiarid climate - semiarid zones - plant ecology - ecology - africa

    Rangelands in Africa provide important forage resources for herbivores; particularly perennial grasses provide grazing for domestic and wild herbivores. However, semi-arid African rangelands experience severe vegetation and soil degradation due to heavy grazing, causing negative impacts on the ecosystems, livestock production and livelihoods of the people. Semi-arid African rangelands can be described by a state-and-transition models, often with three stable states, the first one being a state with ample herbaceous cover, perennial grasses and scattered trees, the second one as a state with a poor cover of annual grasses, absence of perennial grasses, and the third state with a high proportion of bare soil and/or often bush encroached. This thesis aims to fill important information gaps concerning soil seed banks that play in the recovery and possible restoration of degraded semi-arid African rangelands with particular emphasis on Ethiopia. This was done through investigating the mechanisms of how heavy grazing affects the soil seeds bank dynamics so as to understand stable states and transition processes of aboveground vegetation. In this thesis, aboveground vegetation and soil seed bank dynamics were studied under heavy and light grazing pressures in a field and experimental conditions. Results show that heavy grazing resulted in the disappearance of perennial grasses, a reduction in herbaceous species diversity and their plant abundance, standing biomass and basal cover, as well as a decrease in the soil nutrient conditions. The soil seed banks was correlated to differences in grazing pressure, with a greater seedling density under light grazing compared with heavy grazing. Immediately after seed dispersal, the seedling density increased over the first first three months until the eight months of soil sampling, and decreased thereafter. Under light grazing, perennial grass species dominated, whereas annual species were abundant at the heavily grazed sites, indicating that perennial grasses, with good fodder value, are replaced by annual species in the soil seed banks due to heavy grazing. With increasing soil depth, the seedling density and its species richness declined. Moreover, the seeds of perennial grasses were less abundant in the soil seed banks under heavy grazing. The similarity in species composition between the soil seed banks and aboveground vegetation was low under heavy grazing. Results also show that annual grasses had a lower germination and mortality, and higher viability, leading to a longevity of 62% over the 120 days burial in the soil, which was high compared to the 28% for perennials. Moreover, most perennial grasses germinate rapidly after initial seed dispersal at the first rains early in the year, whereas annual grasses show a linear germination pattern over time, indicating that perennial grasses have different survival strategy in semi-arid Africa. As a result, annual species are expected to dominate the soil seed banks, whereas most perennial grass species do not form persistent soil seed banks.The mean mortality from the seedling stage to adult plants in grass species was 65%, and the seed–to–seedling stage was found the most critical transitional stage for grass survival on these rangelands, suggesting that exclusion from grazing and trampling in the early germination stage is important to facilitate the transition from seedling to established plants. Depletion of perennial grass seeds in the soil due to heavy grazing coupled with high seedling mortality leads to a strong decrease in perennial grasses both in the soil seed banks, as well as in the aboveground vegetation. I found that the positive relationship between plant cover and differences in soil seed bank dynamics, i.e., seed density, seed germination rate and longevity, trigger the transition from perennial grasses to annuals and from annual plant cover to bare soil under heavy grazing. I hypothesize that the restoration of perennial grasses from the soil seed banks in heavily grazed areas in semi-arid African rangelands cannot be successful without an extraneous source of perennial grass seeds and without protecting the young plant’s regrowth from trampling and grazing. Therefore, the persistence of species and maintenance of biodiversity in semi-arid rangelands depends mainly on the recruitment of seedlings from annual species, and on vegetative reproduction of perennial grasses and woody species. These findings have important implications for the management, conservation and restoration of semi-arid African rangelands.

    Keywords:Africa; Aboveground vegetation; Ethiopia; Pastoral system; Rangeland; Restoration; Soil seed bank; Savanna; Semi-arid ecosystem; Vegetation and soil degradation

    Shrubs in the cold : interactions between vegetation, permafrost and climate in Siberian tundra
    Blok, D. - \ 2011
    Wageningen University. Promotor(en): Frank Berendse, co-promotor(en): Monique Heijmans; Gabriela Schaepman. - [S.l.] : S.n. - ISBN 9789461730251 - 152
    struiken - vegetatie - permafrost - kou - klimaat - interacties - toendra - arctische ecologie - plantenecologie - siberië - shrubs - vegetation - permafrost - cold - climate - interactions - tundra - arctic ecology - plant ecology - siberia

    The Arctic is experiencing strong increases in air temperature during the last decades. High-latitude tundra regions are very responsive to changes in temperature and may cause a shift in tundra vegetation composition towards greater dominance of deciduous shrubs. With increasing deciduous shrub cover, the surface albedo (proportion of sunlight that is reflected to the atmosphere) may be reduced and lead to air warming by trapping more solar radiation into the Arctic ecosystem. As a result of this warming, thawing of carbon-rich permafrost soils may increase and cause a large greenhouse gas flux to the atmosphere, thus contributing to global warming.

    In my thesis I studied how climate influences shrub growth in the Siberian tundra and how climate-induced changes in shrub cover affect summer permafrost thaw and surface albedo. I investigated these interactions between climate, permafrost and Arctic shrub growth using a combination of shrub ring width analysis, field experiments and remote sensing techniques. I measured and compared growth ring widths with meteorological station data and observed that shrub growth is stimulated by higher summer air temperatures. By performing a shrub removal experiment, I demonstrated that a temperature-induced increase in shrub cover may reduce summer permafrost thaw. Shading by the shrub canopy reduced the transfer of energy to the soil. A denser shrub cover thus effectively reduces summer permafrost thaw, despite leading at the same time to a lower surface albedo. These results indicate it is important to incorporate feedbacks between shrub growth, climate and permafrost thaw in model predictions on the Arctic climate and stability of permafrost in a future warmer world.

    MOVE : MOdel for terrestrial VEgetation version 4.0
    Adrichem, M.H.C. van; Wortelboer, F.G. ; Wamelink, G.W.W. - \ 2010
    Wageningen : Wettelijke Onderzoekstaken Natuur & Milieu (WOt-werkdocument 153) - 182
    vegetatie - milieufactoren - indicatoren - plantenecologie - gebeurtenis - modellen - vegetation - environmental factors - indicators - plant ecology - occurrence - models
    The model MOVE4 predicts the probability of occurrence for over 900 plant species based on the Ellenberg indicator values for acidity, moisture, nutrient availability and salinity, the geophysical region and the vegetation type. The model was developed as a follow up of MOVE3.2. Although extensively tested and applied, the principles and the tests of the model were never laid down. This report fills this gap and contains the principles of MOVE4 and the internal tests that were carried out. The tests show that the model gives reasonable results predicting the probability of occurrence of plant species, but that there is room for improvement.
    Veldgids Plantengemeenschappen
    Schaminee, J.H.J. ; Sykora, K.V. ; Smits, N.A.C. ; Horsthuis, M. - \ 2010
    Zeist : KNNV uitgeverij - ISBN 9789050113090 - 440
    plantengemeenschappen - flora - plantengeografie - plantenecologie - soorten - determinatietabellen - vegetatiekunde - ecologie - nederland - plant communities - flora - phytogeography - plant ecology - species - keys - vegetation science - ecology - netherlands
    Deze gids geeft een compacte beschrijving van alle plantengemeenschappen in Nederland: van open water en moerassen, graslanden en heiden, kust en binnenlandse pioniermilieus, tot ruigten, bossen en struwelen. De gids biedt ook een toegankelijke inleiding over termen en begrippen in de vegetatiekunde. Per plantengemeenschap zijn verspreidingskaartjes, samenvattende tabellen met de belangrijkste soorten en grafieken over standplaats en levensvormen opgenomen. Bovendien bevat het boek determinatiesleutels waarmee de Nederlandse plantengemeenschappen op naam zijn te brengen. De sleutels leiden tot de juiste klasse, waarna aan de hand van standplaatskenmerken en soortensamenstelling op eenvoudige wijze de plantengemeenschap kan worden bepaald.
    Infoblad herstel van akkerflora
    Kloen, H. ; Haveman, R. - \ 2010
    bouwland - vegetatietypen - vegetatiebeheer - plantenecologie - akkerranden - natuurbeheer - arable land - vegetation types - vegetation management - plant ecology - field margins - nature management
    Akkers met een goed ontwikkelde begroeiing van akkerkruiden hebben een grote nostalgische waarde. Het beeld van wuivende korenhalmen, met daartussen het rood van klaprozen, het wit van kamilles en het blauw van korenbloemen appelleert sterk aan ons gevoel van oorspronkelijkheid. Het is mede daardoor dat veel natuurbeheerders proberen om op delen van hun terreinen dit soort akkerflora weer te herstellen. De kleurrijke akkers hebben bovendien niet alleen een grote natuurwaarde, maar ook een belangrijke cultuurhistorische waarde. Tot voor honderd jaar geleden namelijk domineerden graanvelden het Nederlandse landschap. Het beheer en het herstel van deze akkers gaat echter lang niet altijd even goed. Dit infoblad geeft in het kort aan wat de eigenschappen zijn van die typische akkerflora en welke maatregelen kunnen leiden tot het herstel ervan en bovendien wat kansrijke locaties zijn voor het nieuwe natuurakkers.
    Adaptation science for agriculture : solutions for a changing planet
    Meinke, H.B. - \ 2010
    Wageningen : Wageningen UR - ISBN 9789085852711 - 32
    gewasproductie - plantenfysiologie - plantenecologie - systeemanalyse - agro-ecologie - agro-ecosystemen - crop production - plant physiology - plant ecology - systems analysis - agroecology - agroecosystems
    De gezoneerde stekelzwam in de lift
    Dam, N.J. - \ 2009
    Nature Today 2009 (2009)09-09.
    mycologie - paddestoelen - biotopen - plantenecologie - groeiplaatsen - natuurbeheer - mycology - mushrooms - biotopes - plant ecology - sites - nature management
    Hoewel veel paddenstoelen nog steeds achteruit gaan, gaat het beter met de stekelzwammen. Na jaren van achteruitgang is de gezoneerde stekelzwam weer vaker te vinden in met eiken beplante schrale wegbermen. Wellicht verdwijnt de soort zelfs van de Rode Lijst.
    Klimop 2, Ecologische en fysieke gevolgen
    Kopinga, J. - \ 2009
    Bomen, het vakblad voor de boomverzorging 2009 (2009)7. - p. 4 - 9.
    openbare parken - stedelijke gebieden - bomen - hedera helix - plantenontwikkeling - luchtkwaliteit - plantenecologie - gezondheidsgevaren - openbaar groen - groenbeheer - fijn stof - public parks - urban areas - trees - hedera helix - plant development - air quality - plant ecology - health hazards - public green areas - management of urban green areas - particulate matter
    Dit artikel is het tweede in een serie van drie over de toepassing en het beheer van de klimop. Het is gebaseerd op het rapport Klimop in het stedelijk groen, dat schrijver dezes opstelde op verzoek van stadsdeel Amsterdam-Noord. Dit tweede deel gaat over de ecologische en fysieke gevolgen van het toepassen van de klimop in het openbaar groen.
    Darwin's wind hypothesis: does it work for plant dispersal in fragmented habitats?
    Riba, M. ; Mayol, M. ; Giles, B.E. ; Ronce, O. ; Imbert, E. ; Velde, M. van der; Chauvet, S. ; Ericson, L. ; Bijlsma, R. ; Vosman, B. ; Smulders, M.J.M. ; Olivieri, I. - \ 2009
    New Phytologist 183 (2009)3. - ISSN 0028-646X - p. 667 - 677.
    habitatfragmentatie - plantenecologie - klimaatverandering - windeffecten - habitat fragmentation - plant ecology - climatic change - wind effects - seed dispersal - centaurea-corymbosa - island populations - mycelis-muralis - crepis-sancta - gene flow - evolution - metapopulation - range - strategies
    • Using the wind-dispersed plant Mycelis muralis, we examined how landscape fragmentation affects variation in seed traits contributing to dispersal. • Inverse terminal velocity (V(t)¯¹) of field-collected achenes was used as a proxy for individual seed dispersal ability. We related this measure to different metrics of landscape connectivity, at two spatial scales: in a detailed analysis of eight landscapes in Spain and along a latitudinal gradient using 29 landscapes across three European regions. • In the highly patchy Spanish landscapes, seed V(t)¯¹ increased significantly with increasing connectivity. A common garden experiment suggested that differences in V(t)¯¹ may be in part genetically based. The V(t)¯¹ was also found to increase with landscape occupancy, a coarser measure of connectivity, on a much broader (European) scale. Finally, V(t)¯¹ was found to increase along a south–north latitudinal gradient. • Our results for M. muralis are consistent with 'Darwin's wind dispersal hypothesis' that high cost of dispersal may select for lower dispersal ability in fragmented landscapes, as well as with the 'leading edge hypothesis' that most recently colonized populations harbour more dispersive phenotypes.
    Plants on the move: plant-soil interactions in poleward shifting plant species
    Grunsven, R.H.A. van - \ 2008
    Wageningen University. Promotor(en): Frank Berendse; Wim van der Putten, co-promotor(en): Elmar Veenendaal. - [S.l.] : S.n. - ISBN 9789085852513 - 140
    planten - plantenecologie - plantensuccessie - invasies - soorten - bodem - interacties - rizosfeer - bodemflora - bodemfauna - klimaatverandering - bodem-plant relaties - plants - plant ecology - plant succession - invasions - species - soil - interactions - rhizosphere - soil flora - soil fauna - climatic change - soil plant relationships
    As a result of recent global climate change, areas that have previously been climatically unsuitable for species have now become suitable new habitats. Many plant-species are expanding their range polewards, colonizing these newly available areas. If these species are able to expand their range faster than their natural enemies they can become released from these limiting factors. A similar mechanism has been reported for invasive plant species, introduced into foreign continent, which are often found to be released from natural enemies.
    An example of an invasive plant species that is introduced into a foreing contintinent is Carpobrotus edulis. This species was found to be negatively affected by the soil community collected in the native range, while the soil communities from the invaded range did not have an effect on plant performance compared to a sterilized control. I hypothesized that a similar reduction of the negative effects of the soil community can occur when plant species shift their range. This hypothesis was tested in a greenhouse experiment. I compared plant-soil feedbacks of three plant species that have recently expanded their range into The Netherlands, with three related native species. The non-native species experienced a significantly less negative effect of plant-soil feedback than the native plant species.
    Concurrently with these range shifts local climate is changing and this might affect plant-soil feedback as well. In order to test this plant-soil feedbacks of six range expanding and six related native species were compared at two temperatures, 20°C and 25°C daytime temperature. While again native species showed a more negative plant-soil feedback than the non-native species, temperature did not affect the strength or direction of plant-soil feedback.
    Besides pair wise comparisons between native and non-native species in the invaded range, comparisons between the native and non-native range of a range expanding plant can be used to test for effects of range shifts on plant-soil interactions. Rhizosphere soil was collected from populations of Tragopogon dubius in both the native and the recently colonized range. The soil communities from the native range had a more negative effect on plant performance than the soil communities from the invaded range as compared to sterilized controls. T. pratensis, which is native to the entire studied range, did not show this pattern.
    As plant-soil interactions are the net effect of many positive and negative factors the less negative effect of plant-soil feedback can be either a result of more positive or less negative effects of the soil community. One of the mutualistic groups of organisms, the arbuscular mycorrhizal fungi (AMF) are known to be a major factor contributing to ecosystem functioning and to the maintenance of plant biodiversity and the most important soil-borne mutualists for many plants. I therefore focus on this group of soil organisms. I compared the association of T.dubius with AMF in the new part of its range with T. pratensis native to this area. Three measures for plant-fungal affinity were compared between these two plant species; the density of AMF propagules able to colonize the plant, the percentage of root length colonized by arbuscular mycorrhiza, and the composition of the resulting AMF community in the roots. This was done for four replicate soil inocula from different sites in The Netherlands. The two plant species did not differ in any of the tested factors. As there are no differences in the association with the most important mutualist the observed differences in plant-soil interaction are likely an effect of release from negative components in the soil community, e.g. soil pathogens, but further studies are needed to test this.
    Alterations in biotic interactions, through climate change and range shifts, such as a release of soil-borne natural enemies, can have significant effects on the performance of plants. Predictions of future ranges and impact of range expanding plant species on invaded ecosystems can therefore not be accurately made without a thorough understanding of its biotic interactions and the way these interactions are changed by the range shifts.

    Grenzen in beweging, de invloed van recente klimaatverandering op Nederlandse plantengemeenschappen
    Staaij, P. van der; Ozinga, W.A. ; Pierik, M. ; Schaminée, J.H.J. - \ 2008
    Natura 2008 (2008)3. - ISSN 0028-0631 - p. 76 - 78.
    klimaatverandering - plantengeografie - plantenecologie - nederland - plantengemeenschappen - climatic change - phytogeography - plant ecology - netherlands - plant communities
    Het klimaat verandert. De mogelijke effecten van klimaatverandering krijgen in toenemende mate de aandacht die ze verdienen. Slechts weinig onderzoek wordt gedaan naar de effecten in de plantenwereld. Er zijn sinds kort een aantal zeer grote gegevensbestanden beschikbaar. Wat zijn de gevolgen voor de in Nederland voorkomende planten en plantengemeenschappen? Dit artikel is een verkorte weergave van een hoofdstuk over klimaatverandering en plantengeografie in het boek Grenzen in beweging
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