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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    On selection for flowering time plasticity in response to density
    Vermeulen, P.J. - \ 2015
    New Phytologist 205 (2015)1. - ISSN 0028-646X - p. 429 - 439.
    arabidopsis-thaliana - phenotypic plasticity - shade-avoidance - adaptive plasticity - impatiens-capensis - dependent selection - plant-populations - genetic-variation - local adaptation - life-history
    Different genotypes often exhibit opposite plastic responses in the timing of the onset of flowering with increasing plant density. In experimental studies, selection for accelerated flowering is generally found. By contrast, game theoretical studies predict that there should be selection for delayed flowering when competition increases. Combining different optimality criteria, the conditions under which accelerated or delayed flowering in response to density would be selected for are analysed with a logistic growth simulation model. To maximize seed production at the whole-stand level (simple optimization), selection should lead to accelerated flowering at high plant density, unless very short growing seasons select for similar onset of flowering at all densities. By contrast, selection of relative individual fitness will lead to delayed flowering when season length is long and/or growth rates are high. These different results give a potential explanation for the observed differences in direction of the plastic responses within and between species, including homeostasis, as a result of the effect of the variation in season length on the benefits of delayed flowering. This suggests that limited plasticity can evolve without the costs and limits that are currently thought to constrain the evolution of plasticity.
    Bayesian QTL analyses using pedigreed families of an outcrossing specis, with application to fruit firmness in apple
    Bink, M.C.A.M. ; Jansen, J. ; Madduri, M. ; Voorrips, R.E. ; Durel, C.E. ; Kouassi, A.B. ; Laurens, F. ; Mathis, F. ; Gessler, C. ; Gobbin, D. ; Rezzonico, F. ; Patocchi, A. ; Kellerhals, M. ; Boudichevskaia, A. ; Dunemann, F. ; Peil, A. ; Nowicka, A. ; Lata, B. ; Stankiewicz-Kosyl, M. ; Jeziorek, K. ; Pitera, E. ; Soska, A. ; Tomala, K. ; Evans, K.M. ; Fernández-Fernández, F. ; Guerra, W. ; Korbin, M. ; Keller, S. ; Lewandowski, M. ; Plocharski, W. ; Rutkowski, K. ; Zurawicz, E. ; Costa, F. ; Sansavini, S. ; Tartarini, S. ; Komjanc, M. ; Mott, D. ; Antofie, A. ; Lateur, M. ; Rondia, A. ; Gianfranceschi, L. ; Weg, W.E. van de - \ 2014
    Theoretical and Applied Genetics 127 (2014)5. - ISSN 0040-5752 - p. 1073 - 1090.
    quantitative trait loci - x domestica borkh. - quality traits - plant-populations - phenotypic data - genome - relatedness - prediction - cultivars - selection
    Key message - Proof of concept of Bayesian integrated QTL analyses across pedigree-related families from breeding programs of an outbreeding species. Results include QTL confidence intervals, individuals’ genotype probabilities and genomic breeding values. Abstract - Bayesian QTL linkage mapping approaches offer the flexibility to study multiple full sib families with known pedigrees simultaneously. Such a joint analysis increases the probability of detecting these quantitative trait loci (QTL) and provide insight of the magnitude of QTL across different genetic backgrounds. Here, we present an improved Bayesian multi-QTL pedigree-based approach on an outcrossing species using progenies with different (complex) genetic relationships. Different modeling assumptions were studied in the QTL analyses, i.e., the a priori expected number of QTL varied and polygenic effects were considered. The inferences include number of QTL, additive QTL effect sizes and supporting credible intervals, posterior probabilities of QTL genotypes for all individuals in the dataset, and QTL-based as well as genome-wide breeding values. All these features have been implemented in the FlexQTL™ software. We analyzed fruit firmness in a large apple dataset that comprised 1,347 individuals forming 27 full sib families and their known ancestral pedigrees, with genotypes for 87 SSR markers on 17 chromosomes. We report strong or positive evidence for 14 QTL for fruit firmness on eight chromosomes, validating our approach as several of these QTL were reported previously, though dispersed over a series of studies based on single mapping populations. Interpretation of linked QTL was possible via individuals’ QTL genotypes. The correlation between the genomic breeding values and phenotypes was on average 90 %, but varied with the number of detected QTL in a family. The detailed posterior knowledge on QTL of potential parents is critical for the efficiency of marker-assisted breeding.
    Fruit size QTL indentification and the prediction of parental QTL genotypes and breeding values in multiple pedigreed populations of sweet cherry
    Rosyara, U.R. ; Bink, M.C.A.M. ; Weg, W.E. van de; Zhang, G. ; Sebolt, A. ; Dirlewanger, E. ; Quero-Garcia, J. ; Schuster, M. ; Iezzoni, Amy - \ 2013
    Molecular Breeding 32 (2013)4. - ISSN 1380-3743 - p. 875 - 887.
    quantitative trait loci - plant-populations - bayesian-analysis - quality - cross - map - markers - genes - peach - set
    Large fruit size is a critical trait for any new sweet cherry (Prunus avium L.) cultivar, as it is directly related to grower profitability. Therefore, determining the genetic control of fruit size in relevant breeding germplasm is a high priority. The objectives of this study were (1) to determine the number and positions of quantitative trait loci (QTL) for sweet cherry fruit size utilizing data simultaneously from multiple families and their pedigreed ancestors, and (2) to estimate fruit size QTL genotype probabilities and genomic breeding values for the plant materials. The sweet cherry material used was a five-generation pedigree consisting of 23 founders and parents and 424 progeny individuals from four full-sib families, which were phenotyped for fruit size and genotyped with 78 RosCOS single nucleotide polymorphism and 86 simple sequence repeat markers. These data were analyzed by a Bayesian approach implemented in FlexQTL™ software. Six QTL were identified: three on linkage group (G) 2 with one each on groups 1, 3, and 6. Of these QTL, the second G2 QTL and the G6 QTL were previously discovered while other QTL were novel. The predicted QTL genotypes show that some QTL were segregating in all families while other QTL were segregating in a subset of the families. The progeny varied for breeding value, with some progeny having higher breeding values than their parents. The results illustrate the use of multiple pedigree-linked families for integrated QTL mapping in an outbred crop to discover novel QTL and predict QTL genotypes and breeding values.
    Within-population genetic structure in beech (Fagus sylvatica L.) stands characterized by different disturbance histories: does forest management simplify population substructure?
    Piotti, A. ; Leonardi, S. ; Heuertz, M. ; Buiteveld, J. ; Geburek, T. ; Gerber, S. ; Kramer, K. ; Vettori, C. ; Vendramin, G.G. - \ 2013
    PLoS ONE 8 (2013)9. - ISSN 1932-6203 - 9 p.
    european beech - populus-trichocarpa - natural-populations - plant-populations - pollen dispersal - estimating seed - f-statistics - null alleles - douglas-fir - white-pine
    The fine-scale assessment of both spatially and non-spatially distributed genetic variation is crucial to preserve forest genetic resources through appropriate forest management. Cryptic within-population genetic structure may be more common than previously thought in forest tree populations, which has strong implications for the potential of forests to adapt to environmental change. The present study was aimed at comparing within-population genetic structure in European beech (Fagus sylvatica L.) plots experiencing different disturbance levels. Five plot pairs made up by disturbed and undisturbed plots having the same biogeographic history were sampled throughout Europe. Overall, 1298 individuals were analyzed using four highly polymorphic nuclear microsatellite markers (SSRs). Bayesian clustering within plots identified 3 to 11 genetic clusters (within-plot hST ranged from 0.025 to 0.124). The proportion of within-population genetic variation due to genetic substructuring (FCluPlot = 0.067) was higher than the differentiation among the 10 plots (FPlotTot = 0.045). Focusing on the comparison between managed and unmanaged plots, disturbance mostly explains differences in the complexity of within-population genetic structure, determining a reduction of the number of genetic clusters present in a standardized area. Our results show that: i) genetic substructuring needs to be investigated when studying the within-population genetic structure in forest tree populations, and ii) indices describing subtle characteristics of the within-population genetic structure are good candidates for providing early signals of the consequences of forest management, and of disturbance events in general.
    An evolutionary game of leaf dynamics and its consequences for canopy structure
    Hikosaka, K. ; Anten, N.P.R. - \ 2012
    Functional Ecology 26 (2012)5. - ISSN 0269-8463 - p. 1024 - 1032.
    nitrogen-use efficiency - elevated co2 - carbon gain - photosynthetic capacity - xanthium-canadense - plant-populations - individual plants - chenopodium-album - carex-acutiformis - deciduous forest
    1. Canopy photosynthesis models combined with optimization theory have been an important tool to understand environmental responses and interspecific variations in vegetation structure and functioning, but their predictions are often quantitatively incorrect. Although evolutionary game theory and the dynamic modelling of leaf turnover have been suggested useful to solve this problem, there is no model that combines these features. 2. Here, we present such a model of leaf area dynamics that incorporates game theory. 3. Leaf area index (LAI; leaf area per unit ground area) was predicted to increase with an increasing degree of interaction between genetically distinct neighbour plants in light interception. This implies that stands of clonal plants that consist of genetically identical daughter ramets have different LAI from other plants. LAI was also sensitive to the assumed vertical pattern of leaf shedding: LAI was predicted to increase with the degree to which leaves were assumed to be shed from higher positions in the canopy. Our model provides more realistic predictions of LAI than previous static optimization, dynamic optimization or static game theoretical models. 4. We suggest that both leaf dynamics and game theoretical considerations of plant competition are indispensable to scale from individual leaf traits to the structure and functioning of vegetation stands, especially in herbaceous species.
    Comparison of pollen gene flow among four European beech (Fagus sylvatica L.) populations characterized by different management regimes
    Piotti, A. ; Leonardi, S. ; Buiteveld, J. ; Geburek, T. ; Gerber, S. ; Kramer, K. ; Vettori, C. ; Vendramin, G.G. - \ 2012
    Heredity 108 (2012). - ISSN 0018-067X - p. 322 - 331.
    pinus-sylvestris l. - paternity analysis - parentage analysis - mating patterns - silvicultural practices - microsatellite markers - habitat fragmentation - plant-populations - sorbus-torminalis - seed dispersal
    The study of the dispersal capability of a species can provide essential information for the management and conservation of its genetic variability. Comparison of gene flow rates among populations characterized by different management and evolutionary histories allows one to decipher the role of factors such as isolation and tree density on gene movements. We used two paternity analysis approaches and different strategies to handle the possible presence of genotyping errors to obtain robust estimates of pollen flow in four European beech (Fagus sylvatica L.) populations from Austria and France. In each country one of the two plots is located in an unmanaged forest; the other plots are managed with a shelterwood system and inside a colonization area (in Austria and France, respectively). The two paternity analysis approaches provided almost identical estimates of gene flow. In general, we found high pollen immigration (~75% of pollen from outside), with the exception of the plot from a highly isolated forest remnant (~50%). In the two unmanaged plots, the average within-population pollen dispersal distances (from 80 to 184¿m) were higher than previously estimated for beech. From the comparison between the Austrian managed and unmanaged plots, that are only 500¿m apart, we found no evidence that either gene flow or reproductive success distributions were significantly altered by forest management. The investigated phenotypic traits (crown area, height, diameter and flowering phenology) were not significantly related with male reproductive success. Shelterwood seems to have an effect on the distribution of within-population pollen dispersal distances. In the managed plot, pollen dispersal distances were shorter, possibly because adult tree density is three-fold (163 versus 57 trees per hectare) with respect to the unmanaged one
    QTL linkage analysis of connected populations using ancestral marker and pedigree information
    Bink, M.C.A.M. ; Radu Totir, L. ; Braak, C.J.F. ter; Winkler, C.R. ; Boer, M.P. ; Smith, O.S. - \ 2012
    Theoretical and Applied Genetics 124 (2012)6. - ISSN 0040-5752 - p. 1097 - 1113.
    quantitative trait loci - plant-populations - kernel hardness - dough strength - model - maize - selection - families - wheat - identity
    The common assumption in quantitative trait locus (QTL) linkage mapping studies that parents of multiple connected populations are unrelated is unrealistic for many plant breeding programs. We remove this assumption and propose a Bayesian approach that clusters the alleles of the parents of the current mapping populations from locus-specific identity by descent (IBD) matrices that capture ancestral marker and pedigree information. Moreover, we demonstrate how the parental IBD data can be incorporated into a QTL linkage analysis framework by using two approaches: a Threshold IBD model (TIBD) and a Latent Ancestral Allele Model (LAAM). The TIBD and LAAM models are empirically tested via numerical simulation based on the structure of a commercial maize breeding program. The simulations included a pilot dataset with closely linked QTL on a single linkage group and 100 replicated datasets with five linkage groups harboring four unlinked QTL. The simulation results show that including parental IBD data (similarly for TIBD and LAAM) significantly improves the power and particularly accuracy of QTL mapping, e.g., position, effect size and individuals’ genotype probability without significantly increasing computational demand.
    The relative importance of above- versus belowground competition for tree growth and survival during early succession of a tropical moist forest
    Breugel, M. van; Breugel, P. van; Jansen, P.A. ; Martinez-Ramos, M. ; Bongers, F. - \ 2012
    Plant Ecology 213 (2012)1. - ISSN 1385-0237 - p. 25 - 34.
    plant-populations - rain-forests - asymmetric competition - secondary succession - local interference - biomass allocation - light interception - size asymmetry - life-history - dry forest
    Competition between neighboring plants plays a major role in the population dynamics of tree species in the early phases of humid tropical forest succession. We evaluated the relative importance of above- versus below-ground competition during the first years of old-field succession on soil with low fertility in Southern Mexico, using the premise that competition for light is size-asymmetric, unlike competition for nutrients. Plant growth is thus expected to be disproportionally impeded by larger neighbors. We studied how growth and survival of 3.5–5.5 m tall saplings of Cecropia peltata and Trichospermum mexicanum, two pioneer species that dominate the secondary forests in the study region, varied with the abundance and size of neighboring trees in 1–2 year old secondary vegetation. We found that local neighborhood basal area varied 10-fold (3 to 30 cm2 m-2) and explained most of the variation in diameter and height growth of the target saplings. Most growth variables were strongly affected by the neighbors bigger than the focal trees with no significant additive effect of the smaller neighbors, indicating asymmetric competition. Smaller neighbors did have a small but significant additive effect on the diameter growth of Cecropia saplings and stem slenderness of Trichospermum saplings. We conclude that competition for light was more important than belowground competition in this initial phase of moist tropical forest successional, despite the low soil fertility
    Quantifying seed dispersal kernels from truncated seed-tracking data
    Hirsch, B.T. ; Visser, M.D. ; Kays, R. ; Jansen, P.A. - \ 2012
    Methods in Ecology and Evolution 3 (2012)3. - ISSN 2041-210X - p. 595 - 602.
    tropical forests - plant-populations - spatial-patterns - wind dispersal - rain-forest - shadows - consequences - recruitment - dependence - behavior
    1. Seed dispersal is a key biological process that remains poorly documented because dispersing seeds are notoriously hard to track. While long-distance dispersal is thought to be particularly important, seed-tracking studies typically yield incomplete data sets that are biased against long-distance movements. 2. We evaluate an analytical procedure developed by Jansen, Bongers & Hemerik (2004) to infer the tail of a seed dispersal kernel from incomplete frequency distributions of dispersal distances obtained by tracking seeds. This ‘censored tail reconstruction’ (CTR) method treats dispersal distances as waiting times in a survival analysis and censors nonretrieved seeds according to how far they can reliably be tracked. We tested whether CTR can provide unbiased estimates of longdistance movements which typically cannot be tracked with traditional field methods. 3. We used a complete frequency distribution of primary seed dispersal distances of the palm Astrocaryum standleyanum, obtained with telemetric thread tags that allow tracking seeds regardless of the distance moved. We truncated and resampled the data set at various distances, fitted kernel functions on CTR estimates of dispersal distance and determined how well this function approximated the true dispersal kernel. 4. Censored tail reconstruction with truncated data approximated the true dispersal kernel remarkably well but only when the best-fitting function (lognormal) was used. We were able to select the correct function and derive an accurate estimate of the seed dispersal kernel even after censoring 50–60% of the dispersal events. However, CTR results were substantially biased if 5% or more of seeds within the search radius were overlooked by field observers and erroneously censored. Similar results were obtained using additional simulated dispersal kernels. 5. Our study suggests that the CTR method can accurately estimate the dispersal kernel from truncated seed-tracking data if the kernel is a simple decay function. This method will improve our understanding of the spatial patterns of seed movement and should replace the usual practice of omitting nonretrieved seeds fromanalyses in seed-tracking studies
    Genotyping of pedigreed apple breeding material with a genome covering set of SSRs: Trueness to type of cultivars and their parentages
    Evans, K.M. ; Patocchi, A. ; Rezzonico, F. ; Mathis-Jeanneteau, F. ; Durel, C.E. ; Fernandez-Fernandez, F. ; Boudichevskaia, A. ; Dunemann, F. ; Stankiewicz-Kosyl, M. ; Gianfranceschi, L. ; Komjanc, M. ; Lateur, M. ; Madduri, M. ; Noordijk, Y. ; Weg, W.E. van de - \ 2011
    Molecular Breeding 28 (2011)4. - ISSN 1380-3743 - p. 535 - 547.
    plant-populations - resistance - traits
    Apple cultivars and breeding lines that represent much of the diversity currently present in major European breeding programmes and are genetically related by their pedigree were examined for the trueness of their identity and parentage by consistency in marker scores using a genome-covering set of 80 microsatellite (SSR) markers and an ‘identity-by-descent’ approach. One hundred and twenty-five individuals were validated for the trueness-to-type of both their parents and 49 were validated for one of their parents, their second being unknown (23 individuals) or not available in this study (26 individuals). In addition, 15 individuals for which we lacked one of or both the direct parents were validated by consistency with tested parents of earlier generations. Furthermore, the identity of 28 founder cultivars was validated, their marker scores being consistent with descending cultivars and breeding lines. Four of the eight triploids identified were clearly shown to have arisen from unreduced egg cells. The assumed pedigree of 15 further individuals was found to be incorrect; fully consistent pedigrees were suggested for three of the cultivars. The pedigrees of a further eight individuals were confirmed through inference from the molecular data
    Detection and use of QTL for complex traits in multiple environments.
    Eeuwijk, F.A. van; Bink, M.C.A.M. ; Chenu, K. ; Chapman, S.C. - \ 2010
    Current Opinion in Plant Biology 13 (2010)2. - ISSN 1369-5266 - p. 193 - 205.
    model selection approach - chain monte-carlo - mixed-model - water-deficit - leaf growth - experimental crosses - quantitative traits - plant-populations - breeding program - flanking markers
    QTL mapping methods for complex traits are challenged by new developments in marker technology, phenotyping platforms, and breeding methods. In meeting these challenges, QTL mapping approaches will need to also acknowledge the central roles of QTL by environment interactions (QEI) and QTL by trait interactions in the expression of complex traits like yield. This paper presents an overview of mixed model QTL methodology that is suitable for many types of populations and that allows predictive modeling of QEI, both for environmental and developmental gradients. Attention is also given to multi-trait QTL models which are essential to interpret the genetic basis of trait correlations. Biophysical (crop growth) model simulations are proposed as a complement to statistical QTL mapping for the interpretation of the nature of QEI and to investigate better methods for the dissection of complex traits into component traits and their genetic controls
    Identity-by-Descent Matrix Decomposition Using Latent Ancestral Allele Models
    Braak, C.J.F. ter; Boer, M.P. ; Totir, L. ; Winkler, C.R. ; Smith, O.S. ; Bink, M.C.A.M. - \ 2010
    Genetics 185 (2010)3. - ISSN 0016-6731 - p. 1045 - 1057.
    quantitative trait loci - population-structure - plant-populations - genotype data - association - stratification - prediction - regression - selection - markers
    Genetic linkage and association studies are empowered by proper modeling of relatedness among individuals. Such relatedness can be inferred from marker and/or pedigree information. In this study, the genetic relatedness among n inbred individuals at a particular locus is expressed as an n x n square matrix Q. The elements of Q are identity-by-descent probabilities, that is, probabilities that two individuals share an allele descended from a common ancestor. In this representation the definition of the ancestral alleles and their number remains implicit. For human inspection and further analysis, an explicit representation in terms of the ancestral allele origin and the number of alleles is desirable. To this purpose, we decompose the matrix Q by a latent class model with K classes (latent ancestral alleles). Let P be an n x K matrix with assignment probabilities of n individuals to K classes constrained such that every element is nonnegative and each row sums to 1. The problem then amounts to approximating Q by PPT, while disregarding the diagonal elements. This is not an eigenvalue problem because of the constraints on P. An efficient algorithm for calculating P is provided. We indicate the potential utility of the latent ancestral allele model. For representative locus-specific Q matrices constructed for a set of maize inbreds, the proposed model recovered the known ancestry.
    Mixed model approaches for the identification of QTLs within a maize hybrid breeding program.
    Eeuwijk, F.A. van; Boer, M. ; Totir, L. ; Bink, M.C.A.M. ; Wright, D. ; Winkler, C. ; Podlich, D. ; Boldman, K. ; Baumgarten, R. ; Smalley, M. ; Arbelbide, M. ; Braak, C.J.F. ter; Cooper, M. - \ 2010
    Theoretical and Applied Genetics 120 (2010)2. - ISSN 0040-5752 - p. 429 - 440.
    quantitative trait loci - linear unbiased prediction - single-cross performance - environmental covariables - genomewide selection - variance-components - plant-populations - marker data - heterosis - pedigree
    Two outlines for mixed model based approaches to quantitative trait locus (QTL) mapping in existing maize hybrid selection programs are presented: a restricted maximum likelihood (REML) and a Bayesian Markov Chain Monte Carlo (MCMC) approach. The methods use the in-silico-mapping procedure developed by Parisseaux and Bernardo (2004) as a starting point. The original single-point approach is extended to a multi-point approach that facilitates interval mapping procedures. For computational and conceptual reasons, we partition the full set of relationships from founders to parents of hybrids into two types of relations by defining so-called intermediate founders. QTL effects are defined in terms of those intermediate founders. Marker based identity by descent relationships between intermediate founders define structuring matrices for the QTL effects that change along the genome. The dimension of the vector of QTL effects is reduced by the fact that there are fewer intermediate founders than parents. Furthermore, additional reduction in the number of QTL effects follows from the identification of founder groups by various algorithms. As a result, we obtain a powerful mixed model based statistical framework to identify QTLs in genetic backgrounds relevant to the elite germplasm of a commercial breeding program. The identification of such QTLs will provide the foundation for effective marker assisted and genome wide selection strategies. Analyses of an example data set show that QTLs are primarily identified in different heterotic groups and point to complementation of additive QTL effects as an important factor in hybrid performance
    Vegetation succession as affected by decreasing nitrogen deposition, soil characteristics and site management: A modelling approach
    Wamelink, G.W.W. ; Dobben, H.F. van; Berendse, F. - \ 2009
    Forest Ecology and Management 258 (2009)8. - ISSN 0378-1127 - p. 1762 - 1773.
    organic-matter - seminatural vegetation - phosphorus limitation - botanical composition - heathland ecosystems - plant-populations - salt-marsh - forest - dynamics - competition
    After many years of increasing nitrogen deposition, the deposition rates are now decreasing. A major question is whether this will result in the expected positive effects on plant species diversity. Long-term experiments that investigate the effects of decreasing deposition are not available. Model simulations may yield insight into the possible effects of decreasing nitrogen deposition on the vegetation. Therefore we developed the vegetation succession model SUMO which is closely linked to the soil model SMART2. In SUMO, the biomass development of five functional plant types is simulated as a function of nitrogen availability, light interception and management. The model simulates the change in biomass distribution over functional types during the succession from almost bare soil via grassland or heathland to various forest types. The model was validated on three sites in The Netherlands and one site in the UK. The aboveground biomass of two grassland vegetation types was well simulated, as well as the aboveground biomass of heathlands during succession of sod removal. Some of the stages of forest succession were simulated less well, but the calculated biomass in the older stages agreed with measured values. To explore the long-term effect of a decrease in nitrogen deposition, we applied the model to a heathland and a pine stand. In the heathland a major change was predicted as a result of decreasing nitrogen deposition in combination with turf stripping. The dominance of grasses changed into a dominance of dwarf shrubs, whereas at continuing high levels of nitrogen deposition grasses remained dominant. In contrast, the simulations indicated only very small effects of a decreasing N deposition in pine forests. This difference is due to the removal of excess nitrogen by management (turf stripping) in the heathland, whereas the more extensive management in the forest hardly removes any nitrogen from the system. The main conclusion from these examples is that a decrease of nitrogen deposition may retard succession, and consequently increase biodiversity in heathland but probably not in forest. The effects of declining N deposition depend on the amount of N that is removed from the system as a consequence of the various management regimes. (C) 2009 Elsevier B.V. All rights reserved.
    Population dynamics of Garcinia lucida (Clusiaceae) in Cameroonian Atlantic forests.
    Guedje, N.M. ; Lejoly, J. ; Nkongmeneck, B.A. ; Jonkers, W.B.J. - \ 2003
    Forest Ecology and Management 177 (2003). - ISSN 0378-1127 - p. 231 - 241.
    density-dependence - plant-populations - tropical trees - matrix models - growth rate - new-zealand - products - conservation - extraction - impact
    Garcinia lucida Vesque (Clusiaceae) is a highly valued non-timber forest tree. The bark and the seeds are exploited and commercialised for medicinal purposes and palm wine processing in Cameroon, Gabon and Equatorial Guinea. The bark is often removed over almost the entire circumference of the stem, leading to high mortality. To identify the processes or the life stages that influence the population dynamics and to forecast the potential effects of harvesting, a demography study was carried and a matrix model was constructed to characterise the population dynamics of G. lucida in the South Cameroonian Atlantic humid forests. The study revealed that height and diameter growth values were very low and may constitute biological disadvantages for the dynamics of the species. The flowering and fruiting model, the absence of seed dormancy, and the high germination and seedling survival rates constituted advantages for the population dynamics, which is characterised by effective regeneration strategies. Rates of growth, survival and fecundity allowed calculations of transition probabilities of the matrix model. The value of the dominant eigenvalue (lambda) was 1.063, slightly higher than the value expected for stable populations. The sensitivities of lambda to changes showed that the population growth was most sensitive to changes in tree growth, particularly in the seedling stage. Elasticity analysis showed that growth and fecundity elements had much lower contributions to lambda, indicating that the harvesting of seeds may have a low impact on population growth. However, the population growth was highly sensitive to changes in survival probability, particularly among trees of 5-10 cm, diameter at breast height (dbh). The last stages, containing the large reproductive individuals over 10 cm dhb, which are interesting for the bark extraction, accounted for lowest elasticity, indicating that the extraction of bark may have at least a low impact on population growth. Thus, there maybe a good scope for sustainable extraction of G. lucida bark in these stages. The size-class 5-10 cm dbh proved by loop analysis to be the most important reproductive stage for population maintenance. However, individuals in this size-class are also exploited by forest gatherers, and increased exploitation pressure on trees in this size-class is likely to have a considerable impact on the population growth and to compromise the scope for sustainable exploitation of this resource. (C) 2002 Elsevier Science B.V All rights reserved.
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