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See detailModelling carbon fluxes of forest and grassland ecosystems in Western Europe using the CARAIB dynamic vegetation model: evaluation against eddy covariance data.
Henrot, Alexandra-Jane ULg; François, Louis ULg; Dury, Marie ULg et al

in Geophysical Research Abstracts (2015, April), 17

Eddy covariance measurements are an essential resource to understand how ecosystem carbon fluxes react in response to climate change, and to help to evaluate and validate the performance of land surface ... [more ▼]

Eddy covariance measurements are an essential resource to understand how ecosystem carbon fluxes react in response to climate change, and to help to evaluate and validate the performance of land surface and vegetation models at regional and global scale. In the framework of the MASC project (« Modelling and Assessing Surface Change impacts on Belgian and Western European climate »), vegetation dynamics and carbon fluxes of forest and grassland ecosystems simulated by the CARAIB dynamic vegetation model (Dury et al., iForest - Biogeosciences and Forestry, 4:82-99, 2011) are evaluated and validated by comparison of the model predictions with eddy covariance data. Here carbon fluxes (e.g. net ecosystem exchange (NEE), gross primary productivity (GPP), and ecosystem respiration (RECO)) and evapotranspiration (ET) simulated with the CARAIB model are compared with the fluxes measured at several eddy covariance flux tower sites in Belgium and Western Europe, chosen from the FLUXNET global network (http://fluxnet.ornl.gov/). CARAIB is forced either with surface atmospheric variables derived from the global CRU climatology, or with in situ meteorological data. Several tree (e.g. Pinus sylvestris, Fagus sylvatica, Picea abies) and grass species (e.g. Poaceae, Asteraceae) are simulated, depending on the species encountered on the studied sites. The aim of our work is to assess the model ability to reproduce the daily, seasonal and interannual variablility of carbon fluxes and the carbon dynamics of forest and grassland ecosystems in Belgium and Western Europe. [less ▲]

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See detailModelling the dynamics of European ecosystems from the early Holocene to the end of the 21st century with the CARAIB dynamic vegetation model
Dury, Marie ULg

Doctoral thesis (2015)

With the current climate change as background, we worked with the dynamic vegetation model CARAIB (CARbon Assimilation In the Biosphere) to study the functioning and dynamics of European ecosystems under ... [more ▼]

With the current climate change as background, we worked with the dynamic vegetation model CARAIB (CARbon Assimilation In the Biosphere) to study the functioning and dynamics of European ecosystems under changing climatic conditions from the beginning of the Holocene to the end of the 21st century. Originally designed to study the role of vegetation in the global carbon cycle and to reconstruct steady state vegetation distributions under current, past and future climatic conditions, we adapt the CARAIB model to perform transient simulations in order to assess vegetation response to changing climate. For this, we improved the demographic processes represented in the model: the conditions for plant establishment, the response to stresses, the competition between species, the species migration, etc. This new version of the model is first described and its main outputs are evaluated using site-based observations, but primarily remote sensing products. The first study carried out with the new version of CARAIB assessed the response of European forest ecosystems to 21st century climate. The classification of the European vegetation in Bioclimatic Affinity Groups (BAGs, Laurent et al., 2008), based on species traits and climatic tolerances and requirements, as well as the fire module recently implemented were for the first time used in future transient projections. The model was first driven by the ARPEGE/Climate model to illustrate and analyse the potential impacts of climate change on forest productivity and distribution as well as fire intensity over Europe under forcing from different IPCC emission scenarios (B1, A1B and A2). The vegetation model projects for the future more frequent and severe droughts in southern Europe. In these areas, the model indicates that interannual variability of net primary productivity might strongly increase as well as wildfire frequency and intensity, which may have large impacts on vegetation density and distribution. In northern Europe and in the Alps, with reduced temperature variability and positive soil water anomalies, NPP variability tends to decrease. The potential CO2 fertilizing effect was studied assuming constant and increasing atmospheric CO2 concentration in the vegetation model. To quantify the uncertainties in the climate projections and in their potential impacts on ecosystems, the vegetation model was also driven by three regional climate models (KNMI-RACMO2, DMI-HIRHAM5 and HC-HadRM3Q0 RCMs) from the European Union project ENSEMBLES. We continued further the analysis representing the European vegetation at the scale of individual species. A set of 99 species (47 herbs, 12 shrubs and 40 trees) have been prepared in such a way that each BAG of plants used in the first part of this work is represented by several of these species. This ensures to provide a full set of species with the major ecosystem functions represented. Like for the BAGs, the bioclimatic limits of the species were obtained by overlapping species distribution from the Atlas Florae Europaeae (AFE) with climatic data. Since the first study highlighted the importance of climatic variability on plant functioning, we used here a 30-yr time series (and not average climate as usually) to determine species establishment and survival conditions. The comparison between the modelled distributions obtained with new climatic thresholds and observed species distribution reveals that taking a longer climatic time series into account improves the predictions of species spatial pattern. Using this improved representation of current species requirements, we projected potential shifts in species distributions for the end of the century. We spatially evaluated the suitability for species establishment and stresses conditions as well as the disappearance and the potential appearance of species. 18% of tree species and 22% of herb and shrub species (respectively 30% and 64% if the CO2 fertilization effect on species is not taken into account) might experience a loss of 30% or more of their current distribution. Finally we combined different model outputs in an original index evaluating the risk of ecosystem disruption to assess the vulnerability of species and ecosystems to future climate change. The highest values of the index are found in southern Europe indicating that the amplitude of the expected ecosystem changes largely exceeds current interannual variability in this area. If climate is one of the main drivers of species dynamics, rapid climate changes as projected for the 21st century might prevent species to track suitable climatic conditions and fill their potential ranges impeded by dispersal capacity. To assess the actual response of vegetation to climate change, we introduced a species migration module in the dynamic vegetation model. Its calibration and evaluation have been performed on the Holocene period considered as an interesting homologue to current climate change, even if the change rate must have been lower. With the module, we studied the postglacial re-colonization of Europe by two tree species Fagus sylvatica and Picea abies. Using maximum potential migration rates (381 and 450 m yr-1 for beech and spruce) calculated by a species distribution model dealing with demographic and dispersal traits, we evaluated with the dynamic vegetation model the involvement of inter-specific competition but also of high climatic variability on species spatio-temporal dynamics. Considering these abiotic and biotic variables in the migration processes resulted in mean migration rates of 91 (± 38) and 131 (± 73) m yr-1 respectively for Fagus sylvatica and Picea abies. If the comparison with palaeorecords demonstrates the ability of such an approach to reasonably replicate the regional features of the species spatio- temporal progressions, the objective was not to reproduce accurately postglacial species history (still not well known and understood) but rather to determine the relative role of some environmental variables on the migration of the two species through different migration scenarii. It appeared that Holocene beech migration might have been strongly affected by interspecific competition while it is climatic conditions and their variability that might have conditioned the spruce migration. With the different scenarios, we showed that mono-causal explanations cannot however explain the observed timing and pattern at the European scale and we rather give preference to a combination of climate, dispersal and competitive factors, the potential role of anthropogenic disturbances being not studied here. [less ▲]

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See detailModelling seed dispersal and tropical forest regeneration :application to Staudtia kamerunensis in the WWF Lake Tele-Tumba Landscape in DR Congo
Coos, William ULg; Dury, Marie ULg; Trolliet, Franck ULg et al

Poster (2014, June)

Unsustainable hunting and slash-and-burn farming in tropical forests can lead to the empty forest syndrome. It is characterized by the loss of key species essential in the maintenance and regeneration of ... [more ▼]

Unsustainable hunting and slash-and-burn farming in tropical forests can lead to the empty forest syndrome. It is characterized by the loss of key species essential in the maintenance and regeneration of the forest. Indeed the main mechanism of this regeneration is seed dispersal, which for tropical trees is usually driven by animals, and the alteration of this process through a reduction of the disperser population may have serious consequences on forest composition. Computer models are powerful tools to study these processes, not only towards a better understanding of the key mechanisms controlling tropical forest regeneration, but also with the aim of optimising forest management and exploitation to reach a better equilibrium between tropical tree species and their seed dispersers. This study describes a seed dispersal module ultimately developed to analyze the regeneration of the rainforest in the WWF Lake Tele – Lake Tumba Landscape in RD Congo (BIOSERF project funded by Belgian Science Policy). The module has been developed to upgrade the CARAIB dynamic vegetation model, which is used in the BIOSERF project. Data are derived from a field study in which we analyzed seed dispersal of a common tree species (Staudtia kamerunensis) and we determined the community of its main dispersers (largely dominated by the hornbill Bycanistes albotibialis). Additional data (density of S. kamerunensis, habitat use and retention time in the digestive tract of hornbills to simulate dispersal kernel) were obtained from literature and satellite images. Different simulations were performed to represent seed rain over time and a survival rate was applied to show the regeneration. The module was able to provide a percentage of recolonization of degraded places. In the end, this result was compared to field studies, which provide close percentage of recolonization [less ▲]

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See detailModelling the future range and productivity of African tree species. Perspectives and limits
Hambuckers, Alain ULg; Dury, Marie ULg; Tosso, Dji-ndé Félicien ULg et al

Poster (2014, June)

There remains a lack of information on the future of plant species in many parts of Africa under the threads of climate change with the exception of the mountainous areas. Models are valuables tools to ... [more ▼]

There remains a lack of information on the future of plant species in many parts of Africa under the threads of climate change with the exception of the mountainous areas. Models are valuables tools to examine this problem because they permit to extrapolate basic information as simple as species occurrence coming from a restricted number of localities to the entire continent. Niche-based models, like logistic regression or MaxEnt, easily allow fitting empirical relationships between environmental variables related to climate and possibly to soil properties. They produce probabilities of occurrence for the present with good accuracy (calibration phase). Projections for the future are made by switching the explanatory data set with future conditions. These models however are limited by the fact that it is difficult to integrate physiological response to increasing CO2 air concentration. Dynamic vegetation models (DVMs) are process-based models that simulate plant environment (soil water, light intensity at various heights, etc.) and plant physiology (transpiration, CO2 fixation, photosynthesis, respiration, carbon allocation, etc.) from climate variables, soil properties, and elevation. They could be run at various scales, from global to regional or even local scale, and simulate the growth of plant functional types (PFTs), of biological affinity groups (BAGs) or of species. A model like CARAIB is able to simulate PFTs and BAGs growth (occurrence and productivity) with rather good accuracy for Western Europe. For the future, the simulations confirm that the physiological effect of CO2 concentration change is dramatic but not easily foreseeable because it depends on overall fertility of the sites (Dury et al., iForest – Biogeosciences and Forestry, 4:82-99, 2011). From this conclusion, spatial and temporal variations of fertility would have to be introduced in modelling studies to reach more operational conclusions. Questions arising about the future of ecosystem services in tropical countries highlight particular plant species (BIOSERF project funded by the Belgian Science Policy: Sustainability of tropical forest biodiversity and services under climate and human pressure). In this study, we model a set of 11 selected African tree species including several Congolese species with logistic regression, MaxEnt and CARAIB models. The two niche-based-models rather properly simulate the ranges obtained with the alpha-hull polygon method. CARAIB correctly simulates the range of the evergreen species but not of the deciduous trees. We examine how physiological knowledge could be use to improve the model. IN particular, we conclude that bud dormancy breaking representation has to be upgraded in the model because this process is likely to control the range of the species. It should act in combination with the specific bioclimatic constants controlling the hydrological and thermal stress and the germination. Additionally, we examine the evolution of the ranges at the 2050 horizon using one of the most recent socio-economic scenarios. [less ▲]

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See detailModelling the Congo basin ecosystems with a dynamic vegetation model
Dury, Marie ULg; Hambuckers, Alain ULg; Trolliet, Franck ULg et al

Conference (2014, April)

The scarcity of field observations in some parts of the world makes difficult a deep understanding of some ecosystems such as humid tropical forests in Central Africa. Therefore, modelling tools are ... [more ▼]

The scarcity of field observations in some parts of the world makes difficult a deep understanding of some ecosystems such as humid tropical forests in Central Africa. Therefore, modelling tools are interesting alternatives to study those regions even if the lack of data often prevents sharp calibration and validation of the model projections. Dynamic vegetation models (DVMs) are process-based models that simulate shifts in potential vegetation and its associated biogeochemical and hydrological cycles in response to climate. Initially run at the global scale, DVMs can be run at any spatial scale provided that climate and soil data are available. In the framework of the BIOSERF project (“Sustainability of tropical forest biodiversity and services under climate and human pressure”), we use and adapt the CARAIB dynamic vegetation model (Dury et al., iForest - Biogeosciences and Forestry, 4:82-99, 2011) to study the Congo basin vegetation dynamics. The field campaigns have notably allowed the refinement of the vegetation representation from plant functional types (PFTs) to individual species through the collection of parameters such as the specific leaf area or the leaf C:N ratio of common tropical tree species and the location of their present-day occurrences from literature and available database. Here, we test the model ability to reproduce the present spatial and temporal variations of carbon stocks (e.g. biomass, soil carbon) and fluxes (e.g. gross and net primary productivities (GPP and NPP), net ecosystem production (NEP)) as well as the observed distribution of the studied species over the Congo basin. In the lack of abundant and long-term measurements, we compare model results with time series of remote sensing products (e.g. vegetation leaf area index (LAI), GPP and NPP). Several sensitivity tests are presented: we assess consecutively the impacts of the level at which the vegetation is simulated (PFTs or species), the spatial resolution and the initial land cover (potential or human-induced). First, we show simulations over the whole Congo basin at a 0.5◦ spatial resolution. Then, we present high-resolution simulations (1 km) carried out over different areas of the Congo basin, notably the DRC part of the WWF Lake Tele – Lake Tumba Landscape. Studied in the BIOSERF project, this area is characterized by a forest-savannah mosaic but also by swamp and flooded forest. In addition, forward transient projections of the model driven with the outputs of about thirty global cli- mate models (GCMs) from the new Coupled Model Intercomparison Project Phase 5 (CMIP5) will permit to outline the likely response of carbon pools to changing climate over the Congo basin during the 21th century. [less ▲]

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See detailModelling the Congo basin ecosystems with a dynamic vegetation model
Dury, Marie ULg; Hambuckers, Alain ULg; Trolliet, Franck ULg et al

Poster (2014, April)

The scarcity of field observations in some parts of the world makes difficult a deep understanding of some ecosystems such as humid tropical forests in Central Africa. Therefore, modelling tools are ... [more ▼]

The scarcity of field observations in some parts of the world makes difficult a deep understanding of some ecosystems such as humid tropical forests in Central Africa. Therefore, modelling tools are interesting alternatives to study those regions even if the lack of data often prevents sharp calibration and validation of the model projections. Dynamic vegetation models (DVMs) are process-based models that simulate shifts in potential vegetation and its associated biogeochemical and hydrological cycles in response to climate. Initially run at the global scale, DVMs can be run at any spatial scale provided that climate and soil data are available. In the framework of the BIOSERF project (“Sustainability of tropical forest biodiversity and services under climate and human pressure”), we use and adapt the CARAIB dynamic vegetation model (Dury et al., iForest - Biogeosciences and Forestry, 4:82-99, 2011) to study the Congo basin vegetation dynamics. The field campaigns have notably allowed the refinement of the vegetation representation from plant functional types (PFTs) to individual species through the collection of parameters such as the specific leaf area or the leaf C:N ratio of common tropical tree species and the location of their present-day occurrences from literature and available database. Here, we test the model ability to reproduce the present spatial and temporal variations of carbon stocks (e.g. biomass, soil carbon) and fluxes (e.g. gross and net primary productivities (GPP and NPP), net ecosystem production (NEP)) as well as the observed distribution of the studied species over the Congo basin. In the lack of abundant and long-term measurements, we compare model results with time series of remote sensing products (e.g. vegetation leaf area index (LAI), GPP and NPP). Several sensitivity tests are presented: we assess consecutively the impacts of the level at which the vegetation is simulated (PFTs or species), the spatial resolution and the initial land cover (potential or human-induced). First, we show simulations over the whole Congo basin at a 0.5◦ spatial resolution. Then, we present high-resolution simulations (1 km) carried out over different areas of the Congo basin, notably the DRC part of the WWF Lake Tele – Lake Tumba Landscape. Studied in the BIOSERF project, this area is characterized by a forest-savannah mosaic but also by swamp and flooded forest. In addition, forward transient projections of the model driven with the outputs of about thirty global cli- mate models (GCMs) from the new Coupled Model Intercomparison Project Phase 5 (CMIP5) will permit to outline the likely response of carbon pools to changing climate over the Congo basin during the 21th century. [less ▲]

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See detailModelling the Holocene migrational dynamics of Fagus sylvatica L. and Picea abies (L.) H. Karst
Lehsten, Lehsten; Dullinger, Stefan; Hülber, Karl et al

in Global Ecology and Biogeography (2014)

Aim: Vegetation dynamics and the competitive interactions involved are assumed to restrict the ability of species to migrate. But in most migration modelling approaches disturbance-driven succession and ... [more ▼]

Aim: Vegetation dynamics and the competitive interactions involved are assumed to restrict the ability of species to migrate. But in most migration modelling approaches disturbance-driven succession and competition processes are reduced to simple assumptions or are even missing. The aim of this study was to test a combination of a migration model and a dynamic vegetation model to estimate the migration of tree species controlled by climate, environment and local species dynamics such as succession and competition. Location: Europe. Methods: To estimate the effect of vegetation dynamics on the migration of European beech and Norway spruce, we developed a post-process migration tool (LPJ-CATS). This tool integrates outputs of the migration model CATS and the dynamic vegetation model LPJ-GUESS. The model LPJ-CATS relies on a linear dependency between the dispersal kernel and migration rate and is based on the assumption that competition reduces fecundity. Results: Simulating potential migration rates with the CATS model, which does not account for competition and disturbance, resulted in mean Holocene migra- tion rates of 435 ± 55 and 330 ± 95 m year−1 for the two species Picea abies and Fagus sylvatica, respectively. With LPJ-CATS, these mean migration rates were reduced to 250 ± 75 and 170 ± 60 m year−1 for spruce and beech, respectively. Moreover, LPJ-CATS simulated migration pathways of these two species that gen- erally comply well with those documented in the palaeo-records. Main conclusions: Our ‘hybrid’ modelling approach allowed for the simulation of generally realistic Holocene migration rates and pathways of the two study species on a continental scale. It suggests that competition can considerably modify spread rates, but also the magnitude of its effect depends on how close climate conditions are to the niche requirements of a particular species. [less ▲]

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See detailImplementing agricultural land-use in the CARAIB dynamic vegetation model
François, Louis ULg; Jacquemin, Ingrid ULg; Fontaine, Corentin et al

Conference (2014)

CARAIB (Dury et al., iForest - Biogeosciences and Forestry, 4:82-99, 2011) is a state-of-the-art dynamic vegetation model with various modules dealing with (i) soil hydrology, (ii) photosynthesis/stomatal ... [more ▼]

CARAIB (Dury et al., iForest - Biogeosciences and Forestry, 4:82-99, 2011) is a state-of-the-art dynamic vegetation model with various modules dealing with (i) soil hydrology, (ii) photosynthesis/stomatal regulation, (iii) carbon allocation and biomass growth, (iv) litter/soil carbon dynamics, (v) vegetation cover dynamics, (vi) seed dispersal, and (vii) vegetation fires. Climate and atmospheric CO2 are the primary inputs. The model calculates all major water and CO2/carbon fluxes and pools. It can be run with plant functional types or species (up to 100 different species) at various spatial scales, from the municipality to country or continental levels. Within the VOTES project (Fontaine et al., Journal of Land Use Science, 2013, DOI:10.1080/1747423X.2013.786150), the model has been improved to include crops and meadows, and some modules have been written to translate model outputs into quantitative indicators of ecosystem services (e.g., evaluate crop yield from net primary productivity or calculate soil erosion from runoff, slope, grown species and various soil attributes). The model was run over an area covering four municipalities in central Belgium, where land-use is dominated by crops, meadows, housing and some forests and was introduced in the model at the land parcel level. Simulations were also performed for the future. In these simulations, CARAIB was combined with the Aporia Agent-Based Model, to project land-use changes up to 2050. This approach is currently extended within the MASC project (funded by Belgian Science Policy, BELSPO) to the whole Belgian territory (at 1 km2) and to Western Europe (at 20 km x 20 km). [less ▲]

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See detailMiddle Miocene climate and vegetation model reconstructions and their validation with the NECLIME database
François, Louis ULg; Henrot, Alexandra-Jane ULg; Utescher, Torsten et al

in Geophys. Res. Abstracts (2014), 16

The NECLIME database gathers data of the fossil flora recorded at many localities around the world at different times of the Miocene. François et al. (Palaeogeography, Palaeoclimatology, Palaeoecology ... [more ▼]

The NECLIME database gathers data of the fossil flora recorded at many localities around the world at different times of the Miocene. François et al. (Palaeogeography, Palaeoclimatology, Palaeoecology, 304, 359–378, 2011) have presented a new method for evaluating palaeoclimate model simulations from such fossil floras. In this method, palaeovegetation is simulated from climate model outputs, using a dynamic vegetation model. Model vegetation reconstruction is then compared to the vegetation cover indicated by the fossil flora record at the various localities, using a common classification of plant functional types (PFTs) in the data and the model. Here, we apply this method to test several published Middle Miocene climate simulations conducted with General Circulation Models of different complexity: (a) Planet Simulator, (b) FOAM-LMDZ4, (c) MPI-ESM, (d) CCSM3.0 and (4) CESM1.0. Corresponding palaeovegetation distributions are simulated with the CARAIB dynamic vegetation model, in which an upgraded vegetation classification involving 26 PFTs has been imple- mented. The NECLIME palaeoflora data from 154 localities distributed worldwide have been translated in terms of the presence/absence of these PFTs. A comparison of models and data is then undertaken globally and in selected regions of the world, using all available localities. The level of agreement varies among models, among PFTs and among regions. For instance, some models are able to produce tropical and subtropical PFTs in Europe consistently with the data, but the agreement for these PFTs may be much poorer in other parts of the world, such as in northeastern Eurasia. [less ▲]

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See detailTesting palaeoclimate and palaeovegetation model reconstructions with palaeovegetation data : an application to the Middle Miocene
François, Louis ULg; Utescher, Torsten; Hamon, Noémie et al

Poster (2013, April)

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See detailRates of consumption of atmospheric CO2 through the weathering of loess during the next 100 yr of climate change
Goddéris, Y.; Brantley, S. L.; François, Louis ULg et al

in Biogeosciences (2013), 10

Quantifying how C fluxes will change in the future is a complex task for models because of the coupling between climate, hydrology, and biogeochemical reactions. Here we investigate how pedogenesis of the ... [more ▼]

Quantifying how C fluxes will change in the future is a complex task for models because of the coupling between climate, hydrology, and biogeochemical reactions. Here we investigate how pedogenesis of the Peoria loess, which has been weathering for the last 13 kyr, will respond over the next 100 yr of climate change. Using a cascade of numerical models for climate (ARPEGE), vegetation (CARAIB) and weathering (WITCH), we explore the effect of an increase in CO2 of 315 ppmv (1950) to 700 ppmv (2100 projection). The increasing CO2 results in an increase in temperature along the entire transect. In contrast, drainage increases slightly for a focus pedon in the south but decreases strongly in the north. These two variables largely determine the behavior of weathering. In addition, although CO2 production rate increases in the soils in response to global warming, the rate of diffusion back to the atmosphere also increases, maintaining a roughly constant or even decreasing CO2 concentration in the soil gas phase. Our simulations predict that temperature increasing in the next 100 yr causes the weathering rates of the silicates to increase into the future. In contrast, the weathering rate of dolomite – which consumes most of the CO2 – decreases in both end members (south and north) of the transect due to its retrograde solubility. We thus infer slower rates of advance of the dolomite reaction front into the subsurface, and faster rates of advance of the silicate reaction front. However, additional simulations for 9 pedons located along the north–south transect show that the dolomite weathering advance rate will increase in the central part of the Mississippi Valley, owing to a maximum in the response of vertical drainage to the ongoing climate change. The carbonate reaction front can be likened to a terrestrial lysocline because it represents a depth interval over which carbonate dissolution rates increase drastically. However, in contrast to the lower pH and shallower lysocline expected in the oceans with increasing atmospheric CO2, we predict a deeper lysocline in future soils. Furthermore, in the central Mississippi Valley, soil lysocline deepening accelerates but in the south and north the deepening rate slows. This result illustrates the complex behavior of carbonate weathering facing short term global climate change. Predicting the global response of terrestrial weathering to increased atmospheric CO2 and temperature in the future will mostly depend upon our ability to make precise assessments of which areas of the globe increase or decrease in precipitation and soil drainage. [less ▲]

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See detailA plant's perspective of extremes: Terrestrial plant responses to changing climatic variability
Reyer, C.; Leuzinger, S.; Ramming, A. et al

in Global Change Biology (2013), 19

We review observational, experimental and model results on how plants respond to extreme climatic conditions induced by changing climatic variability. Distinguishing between impacts of changing mean ... [more ▼]

We review observational, experimental and model results on how plants respond to extreme climatic conditions induced by changing climatic variability. Distinguishing between impacts of changing mean climatic conditions and changing climatic variability on terrestrial ecosystems is generally underrated in current studies. The goals of our review are thus (1) to identify plant processes that are vulnerable to changes in the variability of climatic variables rather than to changes in their mean, and (2) to depict/evaluate available study designs to quantify responses of plants to changing climatic variability. We find that phenology is largely affected by changing mean climate but also that impacts of climatic variability are much less studied but potentially damaging. We note that plant water relations seem to be very vulnerable to extremes driven by changes in temperature and precipitation and that heatwaves and flooding have stronger impacts on physiological processes than changing mean climate. Moreover, interacting phenological and physiological processes are likely to further complicate plant responses to changing climatic variability. Phenological and physiological processes and their interactions culminate in even more sophisticated responses to changing mean climate and climatic variability at the species and community level. Generally, observational studies are well suited to study plant responses to changing mean climate, but less suitable to gain a mechanistic understanding of plant responses to climatic variability. Experiments seem best suited to simulate extreme events. In models, temporal resolution and model structure are crucial to capture plant responses to changing climatic variability. We highlight that a combination of experimental, observational and /or modeling studies have the potential to overcome important caveats of the respective individual approaches. [less ▲]

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See detailModelling the risk of ecosystem disruption in Europe with a dynamic vegetation model
Dury, Marie ULg

Conference (2012, June)

With unprecedented speed and extent, the projected climate change might lead to a disruption of terrestrial plants functioning in many regions. In the framework of the EcoChange project, the process-based ... [more ▼]

With unprecedented speed and extent, the projected climate change might lead to a disruption of terrestrial plants functioning in many regions. In the framework of the EcoChange project, the process-based dynamic vegetation model, CARAIB DVM (Dury et al., 2011, iForest 4, 82-99) was used to assess the transient vegetation response to climate change and identify threatened regions across Europe. The vegetation model was driven over 1951-2100 by the outputs of 4 climate models under different SRES scenarios: the ARPEGE/Climate model and 3 regional climate models from the European Union project ENSEMBLES. European vegetation was studied at the Bioclimatic Affinity groups scale as well as the species scale. The ability of the climate models to reproduce the present-day climate was evaluated comparing the interannual climate variability simulated by the models with the observed climate variability over 1961-1990 (CRU TS 3.0 dataset). Under the combined effects of projected changes particularly in temperature and precipitations, CARAIB simulates important reductions in the annual soil water content which have large impacts notably on net primary productivity and fire risk in the Mediterranean region but also in other parts of Europe. With this background, the species and biome distributions are projected to be strongly modified. Finally a quantitative index combining some CARAIB outputs evaluates the risk of ecosystem disruption in Europe. [less ▲]

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See detailModelling the risk of ecosystem disruption in Europe with a dynamic vegetation model
Dury, Marie ULg; Hambuckers, Alain ULg; Warnant, Pierre et al

Conference (2012, April)

What will be the European ecosystem responses to future climate? With unprecedented speed and extent, the projected climate change might lead to a disruption of terrestrial plants functioning in many ... [more ▼]

What will be the European ecosystem responses to future climate? With unprecedented speed and extent, the projected climate change might lead to a disruption of terrestrial plants functioning in many regions. In the framework of the EcoChange project, transient projections over the 1901-2100 period have been performed with a process-based dynamic vegetation model, CARAIB DVM (Dury et al., 2011, iForest 4: 82, 99). The vegetation model was driven by the outputs of four climate models under the SRES A1B scenario: the ARPEGE/Climate model and three regional climate models (KNMI-RACMO2 , DMI-HIRHAM5 and HC-HadRM3Q0 RCMs) from the European Union project ENSEMBLES. DVMs are appropriate tools to apprehend potential climate change impacts on ecosystems and identify threatened regions over Europe. CARAIB outputs (soil moisture, runoff, net primary productivity, fire, etc.) were used to characterize the ecosystem evolution. To assess consequences on biodiversity, the evolution of 100 natural common European species (47 herbs, 12 shrubs and 41 trees) has been studied year-to-year over the 1901-2100 period. Under the combined effects of projected changes particularly in temperature and precipitations, CARAIB simulates important reductions in the annual soil water content. The species productivities vary strongly from year to year reaching during the driest years values much lower than present-day average productivity. According to CARAIB, a lot of species might go beyond their water tolerance very frequently, particularly after 2050, due to more intense summer droughts. In the northern part of Europe and in the Alps, with reduced temperature variability and positive soil water anomalies, NPP variability tends to decrease. Regions with more severe droughts might also be affected by an increase of the frequency and intensity of wildfires. With this background, the species distributions might be strongly modified. 15% of tree species and 30% of herb and shrub species (respectively 30% and 60% if the CO2 fertilization effect on species is not taken into account) might experience a loss of 30% or more of their current distribution. Proportions of new species appearance at the end of the century were also studied. Southern Europe might suffer important species extinction while the more suitable climate conditions in northern Europe might lead to a gain in species diversity. [less ▲]

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See detailModelling European tree species distribution change over the Holocene
Dury, Marie ULg; Dullinger, Stefan; Hülber, Karl et al

Conference (2012, March 01)

The postglacial re-colonization of Europe by temperate tree species from a few glacial refugia during the Holocene (10,000 BP) is a very interesting case to study the mechanisms of the vegetation dynamics ... [more ▼]

The postglacial re-colonization of Europe by temperate tree species from a few glacial refugia during the Holocene (10,000 BP) is a very interesting case to study the mechanisms of the vegetation dynamics. The relative roles that played the climate conditions, the species dispersal capacities and the competition between species in the re-colonization rates remain controversial. We investigate these different aspects with the CARAIB dynamic vegetation model (CARAIB DVM). Transient runs were performed over the Holocene using the HadCM3 AOGCM-reconstructed climate. European-wide species migration at 0.5° x 0.5° is represented in the model using migration rates derived from a high resolution cellular automaton, CATS-UPSCALE. Individual tree species migration rates were pre-calculated with CATS-UPSCALE every 1000 years over each grid cell used by the DVM in the climatic conditions reconstructed by the AOGCM. The impacts of competition on plant dispersal are not taken into account by the automaton. Thus, in CARAIB, a function has been constructed to reduce the potential CATS migration rates in competition conditions. It is based on the species dispersal kernel and on the net primary productivity of the different species present on the grid cell. The migration of one species, from its 10,000 BP refugia, is studied within a landscape defined by a set of other species for which no dispersal limitations are assumed. Here, we illustrate the results obtained for two wind-dispersed (Abies alba and Picea abies) and for a no wind-dispersed (Fagus sylvatica) tree species. The speeds and the paths of the postglacial spread obtained with the DVM are compared to the past distributions of the three species reconstructed from pollen and macrofossil data. The Holocene climate conditions simulated by the HadCM3 AOGCM do not constrain the European re-colonization of the studied species, except in Scandinavia at the beginning of the period for Picea abies. We observe that, during the past 10,000 years, species occupied regions where climate conditions were different from present observed species climate requirements, notably in the 10k species refugia. This result may imply that at present the species do not occupy their potential distribution area and thus that the postglacial re-colonization is not completed yet. We also show that species dispersal capacities cannot explain the observed species migration over the Holocene and that competition has played an important role. Indeed, when we use the potential migration rates (no competition), species spread too fast. [less ▲]

Detailed reference viewed: 52 (7 ULg)
See detailModelling European tree species distribution change over the Holocene
Dury, Marie ULg; François, Louis ULg; Warnant, Pierre et al

Conference (2011, September)

The postglacial re-colonization of Europe by temperate tree species from a few glacial refugia during the Holocene (10,000 BP) is a very interesting case to study the mechanisms of the vegetation dynamics ... [more ▼]

The postglacial re-colonization of Europe by temperate tree species from a few glacial refugia during the Holocene (10,000 BP) is a very interesting case to study the mechanisms of the vegetation dynamics. The relative roles that played the climate conditions, the species dispersal capacities and the inter-specific competition in the re-colonization rates remain controversial. We investigate these different aspects with the CARAIB dynamic vegetation model (CARAIB DVM). Transient runs were performed over the Holocene using the HadCM3 AOGCM-reconstructed climate. European-wide species migration at 0.5° x 0.5° is represented in the model using migration rates derived from a high resolution cellular automaton, CATS-UPSCALE. Individual tree species migration rates were pre-calculated with CATS-UPSCALE every 1000 years over each grid cell used by the DVM in the climatic conditions reconstructed by the AOGCM. The impacts of competition between species on plant dispersal are not taken into account by the automaton. Thus, in CARAIB, a function has been constructed to reduce the potential CATS migration rates in competition conditions. It is based on the species dispersal kernel and on the species net primary productivity. The migration of one species, from its 10,000 BP refugia, is studied within a landscape defined by a set of other species for which no dispersal limitations are assumed. Here, we illustrate the results obtained for two wind-dispersed (Abies alba and Picea abies) and for a no wind-dispersed (Fagus sylvatica) tree species. We compare the HadCM3 climate outputs with reconstructions of some climate variables from fossil dataset. The speeds and the paths of the postglacial spread obtained with the DVM are compared to the past distributions of the three species reconstructed from pollen and macrofossil data. The Holocene climate conditions simulated by the HadCM3 AOGCM do not constrain the European re-colonization of the studied species, except in Scandinavia at the beginning of the period for Picea abies. We observe that, during the past 10,000 years, species occupied regions where climate conditions were different from present observed species climate requirements, notably in the 10k species refugia. This result may imply that at present the species do not occupy their potential distribution area and thus that the postglacial re-colonization is not completed yet. We also show that species dispersal capacities cannot explain the observed species migration over the Holocene and that competition has played an important role. Indeed, when we use the potential migration rates (no competition), species migration rates are too fast. [less ▲]

Detailed reference viewed: 41 (6 ULg)
See detailSimulating the Holocene re-colonization of Europe by tree species using dynamic vegetation models
Dury, Marie ULg; Lehsten, Dörte; Warnant, Pierre et al

Poster (2011, July)

Pollen and macro-fossil data collected from various localities in Europe provide the opportunity to reconstruct the speed and the routes of the post-glacial spread of European tree species. Moving from a ... [more ▼]

Pollen and macro-fossil data collected from various localities in Europe provide the opportunity to reconstruct the speed and the routes of the post-glacial spread of European tree species. Moving from a limited number of refugia at the end of the glacial period, tree species have progressively re-colonized the continent through the Holocene at seemingly species-specific migration rates. However, the relative roles of climatic fluctuations, dispersal capacities of individual species, and inter-specific competition in controlling these rates remains controversial. Here, we investigate these different aspects with two dynamic vegetation models (DVM), LPJ-GUESS and CARAIB. Transient runs of both models were performed over the Holocene, using HadCM3 GCM-reconstructed climate. Large-scale species migration at 0.5°x0.5° is represented in these models using migration rates derived from a small-scale cellular automaton, CATS. Individual tree species migration rates were pre-calculated with CATS every 1000 years over each grid cell used by the DVMs in the climatic conditions reconstructed by the GCM. In the DVMs, these migration speeds were influenced by the response to competition from other species. The DVMs were used to study the migration of one species, from its 10 kyr BP refugia, within a landscape defined by a set of other species for which no dispersal limitations are assumed. Here, we illustrate the results obtained for three wind-dispersed tree species: Abies alba, Picea abies, Fagus sylvatica and compare them to their past distributions reconstructed from pollen and macro-fossil data. [less ▲]

Detailed reference viewed: 49 (8 ULg)
See detailAssessing the impacts of present and future interannual climate variability on European ecosystems using a dynamic vegetation model
Dury, Marie ULg; Hambuckers, Alain ULg; Warnant, Pierre et al

Poster (2011, April)

Climate projections indicate changes in mean climate as well as in climate variability and frequency of extreme events for the end of the 21st century compared to present. Since many biological processes ... [more ▼]

Climate projections indicate changes in mean climate as well as in climate variability and frequency of extreme events for the end of the 21st century compared to present. Since many biological processes reach non-reversible thresholds (loss of ability to germinate, mortality, etc.) at some temperatures or soil water values, changes in climate variability have long-term consequences for ecosystem composition, functioning and carbon storage. The CARAIB dynamic vegetation model is used to evaluate and analyse how future climate variability will affect European ecosystems. We examine the impacts of climate change and associated drought episodes on primary productivity (NPP) as well as on fire intensity. CARAIB is driven by the ARPEGE/Climate model and three regional climate models from the European Union project ENSEMBLES (KNMI-RACMO2, DMI-HIRHAM5 and HC-HadRM3Q0 models) forced with the IPCC A1B emission scenario. We analyse the interannual climate variability simulated by those climate models and compare it with the observed climate variability (CRU TS 3.0 historical climate dataset) over the period 1961-1990. None of these climate models can reproduce accurately the present natural climate variability. Therefore, the present NPP interannual variability simulated by CARAIB using climate outputs from the climate models differs from the one obtained with observed climate. For instance, the NPP interannual variability obtained with the ARPEGE/Climate model is significantly overestimated in some parts of Europe, especially in the Mediterranean region, in France, in northern Germany and northern Poland, in the Balkans and in Ukraine. Since discrepancies between modelled and observed current climate variability may also affect NPP variability calculated for the future as well as the intensity and the frequency of severe drought periods and wildfires, comparing the terrestrial ecosystem evolutions obtained with a range of climate models allows to improve the assessment of climate change impacts on ecosystems in the future. Anyway the trend between the present and the future is expected to be more robust. The NPP interannual variability increases in the future with the four climate models as a result of more frequent and more severe soil water stress episodes in southern and Central Europe. The projected climate changes are also likely to induce increased fire risk in the Mediterranean region but also in Central Europe and Russia. [less ▲]

Detailed reference viewed: 47 (11 ULg)
See detailSimulating the Holocene re-colonization of Europe by tree species using dynamic vegetation models
Dury, Marie ULg; Lehsten, Dörte; Dullinger, Stefan et al

Poster (2011, April)

At the beginning of the Holocene (10.000 BP) started a progressive re-colonization of Europe by temperate tree species from a limited number of glacial refugia. To reconstruct the speed, seemingly species ... [more ▼]

At the beginning of the Holocene (10.000 BP) started a progressive re-colonization of Europe by temperate tree species from a limited number of glacial refugia. To reconstruct the speed, seemingly species-specific, and the routes of the postglacial spread of European tree species, fossil records collected from various localities in Europe are invaluable. However, the relative roles of climatic fluctuations, dispersal capacities of individual species, and inter-specific competition in controlling the re-colonization rates remain controversial. We investigate these different aspects with two dynamic vegetation models (DVM), LPJ-GUESS and CARAIB. Transient runs of both models were performed over the Holocene, using HadCM3 GCM-reconstructed climate. Large-scale species migration at 0.5◦ x0.5◦ is represented in these models using migration rates derived from a small-scale cellular automaton, CATS. Individual tree species migration rates were pre-calculated with CATS every 1000 years over each grid cell used by the DVMs in the climatic conditions reconstructed by the GCM. In the DVMs, these migration speeds were influenced by the response to competition from other species, expressed as a function of net primary production ratios. The DVMs were used to study the migration of one species, from its 10.000 BP refugia, within a landscape defined by a set of other species for which no dispersal limitations are assumed. Here, we illustrate the results obtained for wind-dispersed tree species and compare them to their past distributions reconstructed from pollen and macrofossil data. [less ▲]

Detailed reference viewed: 14 (1 ULg)