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.

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    European Mixed Forests: Definition and research perspectives
    Bravo-Oviedo, A. ; Pretzsch, H. ; Ammer, C. ; Andenmatten, E. ; Barbati, A. ; Barreiro, S. ; Brang, P. ; Bravo, F. ; Coll, L. ; Corona, P. ; Ouden, J. den - \ 2014
    Forest Systems 23 (2014)3. - ISSN 2171-5068 - p. 518 - 533.
    stand-density index - fagus-sylvatica l. - species stands - norway spruce - picea-abies - pure stands - biomass allocation - climate-change - biodiversity - productivity
    Aim of study: We aim at (i) developing a reference definition of mixed forests in order to harmonize comparative research in mixed forests and (ii) briefly review the research perspectives in mixed forests. Area of study: The definition is developed in Europe but can be tested worldwide. Material and methods: Review of existent definitions of mixed forests based and literature review encompassing dynamics, management and economic valuation of mixed forests. Main results: A mixed forest is defined as a forest unit, excluding linear formations, where at least two tree species coexist at any developmental stage, sharing common resources (light, water, and/or soil nutrients). The presence of each of the component species is normally quantified as a proportion of the number of stems or of basal area, although volume, biomass or canopy cover as well as proportions by occupied stand area may be used for specific objectives. A variety of structures and patterns of mixtures can occur, and the interactions between the component species and their relative proportions may change over time. The research perspectives identified are (i) species interactions and responses to hazards, (ii) the concept of maximum density in mixed forests, (iii) conversion of monocultures to mixed-species forest and (iv) economic valuation of ecosystem services provided by mixed forests. Research highlights: The definition is considered a high-level one which encompasses previous attempts to define mixed forests. Current fields of research indicate that gradient studies, experimental design approaches, and model simulations are key topics providing new research opportunities.
    Drought response of five conifer species under contrasting water availability suggests high vulnerability of Norway spruce and European larch
    Lévesque, M. ; Saurer, M. ; Siegwolf, R. ; Eilmann, B. ; Brang, P. ; Bugmann, H. ; Rigling, A. - \ 2013
    Global Change Biology 19 (2013)10. - ISSN 1354-1013 - p. 3184 - 3199.
    oxygen-isotope signals - tree-ring width - scots pine - picea-abies - time-series - precipitation series - climate variability - extreme events - pubescent oak - stable carbon
    The ability of tree species to cope with anticipated decrease in water availability is still poorly understood. We evaluated the potential of Norway spruce, Scots pine, European larch, black pine, and Douglas-fir to withstand drought in a drier future climate by analyzing their past growth and physiological responses at a xeric and a mesic site in Central Europe using dendroecological methods. Earlywood, latewood, and total ring width, as well as the d13C and d18O in early- and latewood were measured and statistically related to a multiscalar soil water deficit index from 1961 to 2009. At the xeric site, d13C values of all species were strongly linked to water deficits that lasted longer than 11 months, indicating a long-term cumulative effect on the carbon pool. Trees at the xeric site were particularly sensitive to soil water recharge in the preceding autumn and early spring. The native species European larch and Norway spruce, growing close to their dry distribution limit at the xeric site, were found to be the most vulnerable species to soil water deficits. At the mesic site, summer water availability was critical for all species, whereas water availability prior to the growing season was less important. Trees at the mesic were more vulnerable to water deficits of shorter duration than the xeric site. We conclude that if summers become drier, trees growing on mesic sites will undergo significant growth reductions, whereas at their dry distribution limit in the Alps, tree growth of the highly sensitive spruce and larch may collapse, likely inducing dieback and compromising the provision of ecosystem services. However, the magnitude of these changes will be mediated strongly by soil water recharge in winter and thus water availability at the beginning of the growing season.
    Measurement methods and variability assessment of the Norway spruce total leaf area: Implications for remote sensing
    Homolova, L. ; Lukes, P. ; Malenovsky, Z. ; Lhotakova, Z. ; Kaplan, V. ; Hanus, J. - \ 2013
    Trees-Structure and Function 27 (2013)1. - ISSN 0931-1890 - p. 111 - 121.
    chlorophyll-a - light-interception - hyperspectral data - picea-abies - imaging spectroscopy - conifer needles - surface-area - gas-exchange - canopy - biochemistry
    Estimation of total leaf area (LAT) is important to express biochemical properties in plant ecology and remote sensing studies. A measurement of LAT is easy in broadleaf species, but it remains challenging in coniferous canopies. We proposed a new geometrical model to estimate Norway spruce LAT and compared its accuracy with other five published methods. Further, we assessed variability of the total to projected leaf area conversion factor (CF) within a crown and examined its implications for remotely sensed estimates of leaf chlorophyll content (Cab). We measured morphological and biochemical properties of three most recent needle age classes in three vertical canopy layers of a 30 and 100-year-old spruce stands. Newly introduced geometrical model and the parallelepiped model predicted spruce LAT with an error >5 % of the average needle LAT, whereas two models based on an elliptic approximation of a needle shape underestimated LAT by up to 60 %. The total to projected leaf area conversion factor varied from 2. 5 for shaded to 3. 9 for sun exposed needles and remained invariant with needle age class and forest stand age. Erroneous estimation of an average crown CF by 0. 2 introduced an error of 2-3 µg cm-2 into the crown averaged Cab content. In our study, this error represents 10-15 % of observed crown averaged Cab range (33-53 µg cm-2). Our results demonstrate the importance of accurate LAT estimates for validation of remotely sensed estimates of Cab content in Norway spruce canopies.
    Tree-growth analyses to estimate tree species' drought tolerance
    Eilmann, B. ; Rigling, A. - \ 2012
    Tree Physiology 32 (2012)2. - ISSN 0829-318X - p. 178 - 187.
    pinus-sylvestris l. - scots pine - forest trees - picea-abies - climate - water - mortality - soil - switzerland - responses
    Climate change is challenging forestry management and practices. Among other things, tree species with the ability to cope with more extreme climate conditions have to be identified. However, while environmental factors may severely limit tree growth or even cause tree death, assessing a tree species' potential for surviving future aggravated environmental conditions is rather demanding. The aim of this study was to find a tree-ring-based method suitable for identifying very drought-tolerant species, particularly potential substitute species for Scots pine (Pinus sylvestris L.) in Valais. In this inner-Alpine valley, Scots pine used to be the dominating species for dry forests, but today it suffers from high drought-induced mortality. We investigate the growth response of two native tree species, Scots pine and European larch (Larix decidua Mill.), and two non-native species, black pine (Pinus nigra Arnold) and Douglas fir (Pseudotsuga menziesii Mirb. var. menziesii), to drought. This involved analysing how the radial increment of these species responded to increasing water shortage (abandonment of irrigation) and to increasingly frequent drought years. Black pine and Douglas fir are able to cope with drought better than Scots pine and larch, as they show relatively high radial growth even after irrigation has been stopped and a plastic growth response to drought years. European larch does not seem to be able to cope with these dry conditions as it lacks the ability to recover from drought years. The analysis of trees' short-term response to extreme climate events seems to be the most promising and suitable method for detecting how tolerant a tree species is towards drought. However, combining all the methods used in this study provides a complete picture of how water shortage could limit species.
    Crown plasticity and neighborhood interactions of European beech (Fagus sylvatica L.) in an old-growth forest
    Schröter, M. ; Härdtle, W. ; Oheimb, G. von - \ 2012
    European Journal of Forest Research 131 (2012)3. - ISSN 1612-4669 - p. 787 - 798.
    tree canopy displacement - norway spruce - stand level - dead wood - mixed stands - picea-abies - asymmetry - dynamics - competition - patterns
    Competition for canopy space is a process of major importance in forest dynamics. Although virgin and old-growth European beech (Fagus sylvatica L.) forests in Europe have been studied for many years, there are to date no studies of individual-tree crown plasticity and the way this is influenced by local neighborhood interactions in these forests. In this study, we analyzed crown plasticity and local neighborhood interactions of individual trees in the upper canopy of the old-growth beech forests of Serrahn, northeast Germany. In a 2.8-ha sample plot, we measured crown radii of all upper canopy trees and analyzed the direction and extent of crown asymmetry. Size, relative position, and distance of neighboring trees were used to construct vectors of neighborhood asymmetry within different distances from target trees. The crowns of beech trees showed strong morphological plasticity. Mean absolute and relative displacement of crown centers from the stem base were 1.95 m and 0.37, respectively. Circular–circular rank correlation coefficients between the direction of crown displacement and the direction of neighborhood pressure showed that trees strongly positioned their crowns away from local neighbors. Highest correlation coefficients were obtained when basal area and relative position of neighboring trees within a radial distance of 12 m were considered. Clark and Evans index and Ripley’s K-function showed that crowns were more regularly distributed than stems. Projected canopy cover was about 10% higher than canopy cover with simulated circular crowns. We conclude that the crowns of older beech trees have a high ability to plastically respond to changes in the local canopy conditions, enabling very effective exploitation of canopy space.
    Long-term effects of ungulate browsing on forest composition and structure
    Didion, M.P. ; Kupferschmid, A.D. ; Bugmann, H. - \ 2009
    Forest Ecology and Management 258 (2009)Suppl.1. - ISSN 0378-1127 - p. S44 - S55.
    white-tailed deer - mountain forests - european alps - gap model - roe deer - population-dynamics - species composition - protection forests - picea-abies - impact
    The impact of ungulate herbivores on tree regeneration and its possible consequences for long-term forest dynamics has raised concerns worldwide. In many countries, ungulate management aims at constant animal densities, whereas unmanaged ungulate populations tend to fluctuate over time. The ecosystem consequences of constant vs. varying ungulate densities are largely unknown, and the exact density that is acceptable from a forestry point of view is highly uncertain as well. We used the gap model ForClim v2.9.5 to examine the effects of three browsing-related phenomena: (a) temporal changes in animal densities and thus oscillations in browsing intensity; (b) changes in the importance of browsing as a limiting factor relative to other limitations for ingrowth; and (c) growth suppression by browsing and hence different ingrowth rates for slow- vs. fast-growing trees. Results showed that ungulate herbivory can induce profound compositional and structural changes in forest stands: (a) oscillations in the browsing intensity led to compositional shifts that were less severe than under the corresponding constant browsing intensity; (b) an increase in the importance of browsing relative to other environmental factors caused a decrease in the incidence of palatable species; and (c) growth suppression strongly affected the numbers and composition of small trees of all species. We conclude that browsing can cause a shift not only in the structure and composition of tree regeneration, but also of the upper canopy in the long term. Management can manipulate forest ecosystems through the control of animal densities, and our results suggest that alternative management strategies for ungulate populations may be worth considering so as to provide “windows of opportunity” for forest regeneration in time and/or space.
    Analyses of the impact of changes in atmospheric deposition and climate on forest growth in European monitoring plots: A stand growth approach
    Solberg, S. ; Dobbertin, M. ; Reinds, G.J. ; Andreassen, K. ; Lange, H. ; Garcia Fernandez, P. ; Hildingsson, A. ; Vries, W. de - \ 2009
    Forest Ecology and Management 258 (2009)8. - ISSN 0378-1127 - p. 1735 - 1750.
    nitrogen deposition - acid deposition - picea-abies - tree growth - carbon sequestration - soil acidification - density index - norway - spruce - responses
    During the last 15 years a number of studies have shown increasing forest growth in central Europe, rather than a decline as was expected due to negative effects of air pollution. We have here used data from intensive monitoring plots spread over Europe for a five year period in order to examine the influence of environmental factors on forest growth. Evaluations focussed on the influence of nitrogen, sulphur and acid deposition, temperatures, precipitation and on a drought index calculated as deviation from the long-term mean. The study included the main tree species Norway spruce, Scots pine, common beech as well as European and sessile oak and was based on data from 363 plots. As many other factors besides nitrogen and temperature influence tree growth, expected stem volume increments were modelled using site productivity, stand age and a stand density index. Relative volume increment was then calculated as actual increment in % of expected increment. The site productivity, assumed to be given by site conditions and past environmental conditions, was either taken from expert estimates or computed from site index curves from northern, central and southern Europe. The model explained between 18% and 39% of the variance with site productivity being positively related and age negatively related to actual increment. The various models and statistical approaches were fairly consistent, and indicated a fertilizing effect of nitrogen deposition, with slightly above one percent increase in volume increment per kg of nitrogen deposition per ha and year. This was most clear for spruce and pine, and most pronounced for plots having soil C/N ratios above 25. Also, we found a positive relationship between relative increment and summer temperature, i.e. May–August mean temperature deviation from the 1961–1990 means. The cause–effect relationship here is, however, less certain. Other influences were uncertain. Possibly, sulphur and acid deposition have effects on growth, but these effects are obscured by, and outweighed by the positive effect of nitrogen deposition, because of collinearity between these variables. Drought effects were uncertain also, and one reason for this might be large uncertainties in the precipitation data: precipitation measured on some 50% of the plots correlated poorly with the precipitation data obtained from Europe-wide databases. The major finding of this study was a positive relationship between higher than normal volume increment on one hand and nitrogen deposition on the other hand.
    Hydrolytic stability of water-soluble spruce O-acetyl galactoglucomannans
    Xu, C. ; Pranovich, A. ; Hemmimg, J. ; Holmbom, B. ; Albrecht, S.A. ; Schols, H.A. ; Willfor, S. - \ 2009
    Holzforschung 63 (2009)1. - ISSN 0018-3830 - p. 61 - 68.
    molecular-weight changes - norway spruce - thermomechanical pulp - acid-hydrolysis - picea-abies - degradation - kinetics - chitosan - polymer
    Water-soluble native O-acetyl galactoglucomannan (GGM) from spruce is a polysaccharide that can be produced in an industrial scale. To develop GGM applications, information is needed on its stability, particularly under acidic conditions. Therefore, acid hydrolysis of spruce GGM was investigated at various pH levels and temperatures. The results allow an estimation of the stability of GGM under food processing conditions and in biological systems. Determination of the average molar mass demonstrated that spruce GGM was stable at pH 1 and 37°C, as well as at pH 3 and 70°C. GGM was hydrolysed at pH 1 and 90°C. GGM oligomers and monomers were detected after degradation. Some of the oligomers contained O-acetyl groups. Monosaccharides were the predominant products in the hydrolysates after treatment at pH 1 and 90°C for 48 h. Pentoses, present in GGM samples as impurities, were released more easily than GGM hexoses. Glucose was more difficult to release than mannose. Traces of 6-deoxy-mannose and levoglucosan were found in the hydrolysates, indicating further degradation of hydrolysed monosaccharides.
    The wind stability of different silvicultural systems for Douglas-fir in The Netherlands: a model-based approach
    Schelhaas, M.J. - \ 2008
    Forestry 81 (2008)3. - ISSN 0015-752X - p. 399 - 414.
    forest stands - sitka spruce - density management - field-measurements - coniferous trees - fagus-sylvatica - picea-abies - damage - growth - soil
    The aim of this study was to evaluate different silvicultural systems for Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) in the Netherlands in terms of timber production and wind stability over a full rotation. This was done using the forest genetics, ecology, management and wind model (ForGEM-W), which combines a distant dependent tree growth simulator with a mechanical¿empirical wind damage module. Six different silvicultural systems were evaluated: normal yield table management, free thinning from above in a monospecies and a mixed stand (50 per cent mixture of beech (Fagus sylvatica L.)), uneven-aged system, no thinning regime with low initial stand density of Douglas-fir with and without admixture of beech. Silvicultural systems leading to low height¿diameter (h/d) ratios were most successful in avoiding damage. Low h/d ratios were obtained in the system with low stand density and no thinning and in the uneven-aged system by systematically removing trees with the highest ratios during thinning. In particular, the uneven-aged system combined a high timber production with low risk. The use of Douglas-fir¿beech mixtures changed the competition pressure on Douglas-fir, and thus the h/d ratio and the wind risk. Results from this study indicate that the current trend towards more nature-oriented management could lead to lower wind risks and even to an increase in overall productivity.
    Ectomycorrhizal fungal diversity: seperating the wheat from the chaff
    Rinaldi, A.C. ; Comandini, O. ; Kuyper, T.W. - \ 2008
    Fungal Diversity 33 (2008). - ISSN 1560-2745 - p. 1 - 45.
    truffle-like fungi - n-15 isotopic fractionation - ribosomal dna-sequences - pure culture synthesis - mixed-conifer forest - picea-abies - norway spruce - molecular phylogeny - douglas-fir - new-zealand
    Thousands of ectomycorrhizal (ECM) fungal species exist, but estimates of global species richness of ECM fungi differ widely. Many genera have been proposed as being ECM, but ill a number of studies evidence for the hypothesized ECM habit is lacking. Progress in estimating ECM species richness is therefore slow. Ill this paper we have retrieved studies providing evidence for the ECM habit of fungal species and For the identification of the mycobiont(s) ill specific ECM associations, using published and web-based mycorrhiza literature. The identification methods considered are morpho-anatomical, characterization or naturally occurring ECMs, pure Culture synthesis, molecular identification, and isotopic evidence. In addition, phylogenetic information is also considered as a relevant criterion to assess ECM habit. OF 343 fungal genera for which all ECM status has been alleged, about two thirds have Supportive published evidence or ECM Status can be at least hypothesized. For the remaining taxa, Currently no indication exists as for their I-CM nutritional habit, besides field observations or associations with putative hosts. Our survey clearly indicates that current knowledge of ECM fungal diversity, as Supported by experimental evidence, is only partly complete, and that inclusion of many Funga genera in this trophic and ecological category is not verified at this stage. Care must thus be used when compiling lists of ECM and saprotrophic full studies oil the basis of published information only. On the basis of our literature search we conservatively estimate ECM species richness around 7750 species. However, oil the basis of estimates of knowns and unknowns in macromycete diversity, a final estimate or ECM species richness Would likely be between 20000 and 25000.
    Hotspots of the European forests carbon cycle
    Nabuurs, G.J. ; Thürig, E. ; Heidema, N. ; Armolaitis, K. ; Biber, P. ; Cieciala, E. ; Kaufmann, E. ; Mäkipää, R. ; Nilsen, P. ; Petritsch, R. ; Pristova, T. ; Rock, J. ; Schelhaas, M.J. ; Sievanen, R. ; Somogyi, Z. ; Vallet, P. - \ 2008
    Forest Ecology and Management 256 (2008)3. - ISSN 0378-1127 - p. 194 - 200.
    bosecologie - koolstofcyclus - broeikasgassen - milieubeleid - europa - forest ecology - carbon cycle - greenhouse gases - environmental policy - europe - norway spruce - whole-tree - compensatory fertilization - rotation length - managed forests - climate-change - meta analysis - picea-abies - storage - stands
    This paper is the outcome of a group discussion held at the Savonlinna meeting `Management of forest ecosystems and its impact on the GHG budget¿. The aim of this break-out group discussion was to `Characterize forest management impacts on the GHG budget of forest ecosystems in different European regions¿. In this paper we briefly characterize different options that a forest owner has in order to maintain or maximize forest carbon pools and carbon sequestration. These hectare scale descriptions of measures are then regarded in connection to the current state of European forests and how they can be combined with ongoing management trends and local issues. We point out the various possibilities that exist in European forests, where they are located, and where they could possibly be combined with adaptation. We identify these hotspots for largest growing stocks, largest peat areas, and, e.g. largest risks for loss of carbon due to fire or urban sprawl. We conclude that one common strategy cannot be designed. Within each region, local solutions have to be found that optimize goals and aim at integrated and sustainable land use
    A framework for modelling the annual cycle of trees in boreal and temperate regions
    Hänninen, H. ; Kramer, K. - \ 2007
    Silva Fennica 41 (2007)1. - ISSN 0037-5330 - p. 167 - 205.
    red-osier dogwood - betula-pendula seedlings - spring frost damage - cornus-sericea l - scots pine - norway spruce - bud burst - dormancy release - climate-change - picea-abies
    Models of the annual development cycle of trees in boreal and temperate regions were reviewed and classified on the basis of their ecophysiological assumptions. In our classification we discern two main categories of tree development: 1) fixed sequence development, which refers to irreversible ontogenetic development leading to visible phenological events such as bud burst or flowering, and 2) fluctuating development, which refers to reversible physiological phenomena such as the dynamics of frost hardiness during winter. As many of the physiological phenomena are partially reversible, we also describe integrated models, which include aspects of both fixed-sequence and fluctuating development. In our classification we further discern simple E-models, where the environmental response stays constant, and more comprehensive ES-models, where the environmental response changes according to the state of development. On the basis of this model classification, we have developed an operational modelling framework, in which we define an explicit state variable and a corresponding rate variable for each attribute of the annual cycle considered. We introduce a unifying notation, which we also use when presenting a selection of previously published models. To illustrate the various developmental phenomena and their modelling, we have carried out model simulations. Finally, we discuss the ecophysiological interpretation of the model variables, methodological aspects of the empirical development and testing of the models, the introduction of new aspects to the modelling, other closely related models, and applications of the models.
    Ectomycorrhizal weathering of the soil minerals muscovite and hornblende
    Schöll, L. van; Smits, M.M. ; Hoffland, E. - \ 2006
    New Phytologist 171 (2006)4. - ISSN 0028-646X - p. 805 - 814.
    pinus-sylvestris seedlings - forest soil - in-vitro - mg2+ deficiency - organic-acids - picea-abies - fungi - roots - mobilization - dissolution
    Ectomycorrhizal fungi are hypothesized to enhance mineral weathering in forest soils. Several studies have shown an increased uptake of mineral-derived nutrients by trees when in symbiosis with ectomycorrhizal fungi. However, it is difficult to determine from these studies if the improved nutrient uptake is the result of increased weathering or better exploitation of the substrate by the ectomycorrhizal fungi. In a pot experiment, Pinus sylvestris (Scots pine) seedlings were grown with or without ectomycorrhizal fungi, and with or without the mineral muscovite as the only potassium (K) source or the mineral hornblende as the only magnesium (Mg) source. After 27 wk, all pools of non-mineral-bound K or Mg were determined. The ectomycorrhizal fungus Paxillus involutus increased weathering of muscovite but not hornblende. The other ectomycorrhizal fungi tested, Piloderma croceum and Suillus bovinus, did not increase weathering of either muscovite or hornblende compared with the nonmycorrhizal trees. The P. involutus-mediated mobilization of K from muscovite resulted in increased K content of root plus adhering hyphae, but not of shoots. In conclusion, ectomycorrhizal fungi may increase weathering of minerals in response to nutrient deficiencies, but this response is species specific
    Improved fallows: effects of species interaction on growth and productivity in monoculture and mixed stands
    Gathumbi, S.M. ; Cadisch, G. ; Giller, K.E. - \ 2004
    Forest Ecology and Management 187 (2004)2-3. - ISSN 0378-1127 - p. 267 - 280.
    planted fallows - picea-abies - maize yield - nitrogen - plantations - dynamics - mixtures - capture - legumes
    To derive optimal benefits from short-term planted legume fallows, farmers need to make important initial decisions on the establishment and growth performance of specific species in monoculture stands and in mixtures. We hypothesized that species with contrasting growth characteristics could be mixed to optimize aboveground resource capture due to their complementary or compensatory gains in resource acquisition. A selection of tree/shrub/herbaceous legumes planted in monoculture and mixed stands were evaluated for growth, biomass and nitrogen productivity on a Kandiudalfic Eutrudox in western Kenya. Species evaluated included: sesbania (Sesbania sesban (L.) Merr.), crotalaria (Crotalaria grahamiana Wight and Am.), pigeonpea (Cajanus cajan (L.) Millsp.), and siratro (Macroptilium arropurpureum (DC.) Urb). Total aboveground biomass ranged from 5 to 12 Mg ha(-1) (monocultures) and 3.4-8 Mg ha(-1) (mixtures). N yield per plant was linearly correlated with total plant biomass (R-2 = 0.95, slope = 0.018) across all of the fallows, despite different amounts of leaf and wood with widely differing N concentrations being present with the different species. Biomass and N yield of sesbania was negatively affected by mixing with other species. For instance, sesbania N yield decreased when mixed with pigeonpea (54%) or crotalaria (67%). Crotalaria and pigeonpea established best under relay cropping with maize and emerged to be better competitors in mixtures than sesbania and siratro. Results of this study suggest that mixing species in fallows provide a better risk management strategy through compensatory biomass and nutrient production gains obtained from the strongly competing species. (C) 2003 Elsevier B.V. All rights reserved.
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