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See detailChapter 4. Multidisciplinary approaches for conservation issues
Cheddadi, Rachid; Sarmiento, Fausto; Hambuckers, Alain ULiege et al

in Sarmiento, Fausto (Ed.) International handbook of Geography and Sustainability (in press)

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See detailRefining the outputs of a dynamic vegetation model (CARAIB):Research at ULiège, Belgium
Hambuckers, Alain ULiege; Paillet, Marc ULiege; Henrot, Alexandra-Jane ULiege et al

Scientific conference (2019, March 19)

Dynamic vegetation models (DVMs) are process-based models combining the inputs and the outputs of sub-models, possibly in feedback loops, to simulate the plant functions. The sub-models compute conditions ... [more ▼]

Dynamic vegetation models (DVMs) are process-based models combining the inputs and the outputs of sub-models, possibly in feedback loops, to simulate the plant functions. The sub-models compute conditions outside and inside the plant and physiological reactions from the environmental data (climate, light intensity, air CO2 concentration, soil properties). DVMs are tools of choice to predict the future and the past of the vegetation taking into account climatic variations. The emergence of new questions in the context of climate change, particularly on threatened species or on commercial species, compels to apply DVMs to species while the information to parameterize and validate them is largely lacking. Of particular importance are the morpho-physiological traits. These were intensively studied within the hypothesis that they could be used to predict plant performances. This hypothesis finally revealed not very suitable, but it brought to light that important traits controlling photosynthesis and water relationships could strongly vary within each species in response to environmental conditions. We studied the Atlas cedar (Cedrus atlantica (Endl.) Manetti ex Carrière), in Morocco (northern Africa). It is a threatened tree species of important economic value. We also studied the English oak (Quercus robur L.) and the sessile oak (Quercus petraea (Matt.) Liebl.) in eastern Belgium. In a series of localities, we determined several traits (specific leaf area, leaf C/N, sapwood C/N, as well as for the cedar, leaf longevity) and we assessed biomass and net primary productivity as validation data, thanks to forest inventories, dendrochronology analyses and allometric equations combined with leaf area index estimations. We compared the model simulations of the CARAIB DVM when varying the set of traits (direct site estimates or default values) to the field estimates of biomass and net primary productivity. We found that trait default values provide sufficient information for the DVM to compute mean output values but low ability to reproduce between site variations. On the contrary, the in situ traits improve drastically this ability, which indicates that the plant performances are the results of acclimation to the evolving local environmental conditions. [less ▲]

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See detailRefining the outputs of a dynamic vegetation model (CARAIB): the importance of plant traits to improve prediction accuracy at tree species level
Hambuckers, Alain ULiege; Paillet, Marc ULiege; Henrot, Alexandra-Jane ULiege et al

Conference (2019, March 11)

Dynamic vegetation models (DVMs) are process-based models combining the inputs and the outputs of sub-models, possibly in feedback loops, to simulate the plant functions. The sub-models compute conditions ... [more ▼]

Dynamic vegetation models (DVMs) are process-based models combining the inputs and the outputs of sub-models, possibly in feedback loops, to simulate the plant functions. The sub-models compute conditions outside and inside the plant and physiological reactions from the environmental data (climate, light intensity, air CO2 concentration, soil properties). DVMs are tools of choice to predict the future and the past of the vegetation taking into account climatic variations. The emergence of new questions in the context of climate change, particularly on threatened species or on commercial species, compels to apply DVMs to species while the information to parameterize and validate them is largely lacking. Of particular importance are the morpho-physiological traits. These were intensively studied within the hypothesis that they could be used to predict plant performances. This hypothesis finally revealed not very suitable, but it brought to light that important traits controlling photosynthesis and water relationships could strongly vary within each species in response to environmental conditions. We studied the Atlas cedar (Cedrus atlantica (Endl.) Manetti ex Carrière), in Morocco (northern Africa). It is a threatened tree species of important economic value. We also studied the English oak (Quercus robur L.) and the sessile oak (Quercus petraea (Matt.) Liebl.) in eastern Belgium. In a series of localities, we determined several traits (specific leaf area, leaf C/N, sapwood C/N, as well as for the cedar, leaf longevity) and we assessed biomass and net primary productivity as validation data, thanks to forest inventories, dendrochronology analyses and allometric equations combined with leaf area index estimations. We compared the model simulations of the CARAIB DVM when varying the set of traits (direct site estimates or default values) to the field estimates of biomass and net primary productivity. We found that trait default values provide sufficient information for the DVM to compute mean output values but low ability to reproduce between site variations. On the contrary, the in situ traits improve drastically this ability, which indicates that the plant performances are the results of acclimation to the evolving local environmental conditions. [less ▲]

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See detailContrasting climate risks predicted by dynamic vegetation and ecological niche-based models applied to tree species in the Brazilian Atlantic Forest
Raghunathan, Poornima ULiege; François, Louis ULiege; Dury, Marie ULiege et al

in Regional and Environmental Change (2019), 19

Climate change is a threat to natural ecosystems. To evaluate this threat and, where possible, respond, it is useful to understand the potential impacts climate change could have on species’ distributions ... [more ▼]

Climate change is a threat to natural ecosystems. To evaluate this threat and, where possible, respond, it is useful to understand the potential impacts climate change could have on species’ distributions, phenology, and productivity. Here, we compare future scenario outcomes between a dynamic vegetation model (DVM; CARbon Assimilation In the Biosphere (CARAIB)) and an ecological niche-based model (ENM; maximum entropy model) to outline the risks to tree species in the Brazilian Atlantic Forest, comprising the habitats of several endemic species, including the endangered primate Leontopithecus chrysomelas (golden-headed lion tamarin; GHLT), our species of interest. Compared to MaxENT, theDVMpredicts larger present-day species ranges. Conversely, MaxENT ranges are closer to sampled distributions of the realised niches. MaxENT results for two future scenarios in four general circulation models suggest that up to 75% of the species risk losing more than half of their original distribution. CARAIB simulations are more optimistic in scenarios with and without accounting for potential plant-physiological effects of increased CO2, with less than 10% of the species losing more than 50% of their range. Potential gains in distribution outside the original area do not necessarily diminish risks to species, as the potential new zones may not be easy to colonise. It will also depend on the tree species’ dispersal ability. So far, within the current range of L. chrysomelas, CARAIB continues to predict persistence of most resource trees, while MaxENT predicts the loss of up to 19 species out of the 59 simulated. This research highlights the importance of choosing the appropriate modelling approach and interpretation of results to understand key processes. [less ▲]

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See detailDynamics and evolution of Turgay‐type vegetation in Western Siberia throughout the early Oligocene to earliest Miocene—a study based on diversity of plant functional types in the carpological record
Popova, Svetlana; Utescher, Torsten; Gromyko, Dimitry et al

in Journal of Systematics and Evolution (2019), 57(2), 129-141

Based on ecospectra of 66 published carpofloras we study dynamics and evolution of Turgay vegetation in Western Siberia during the early Oligocene to earliest Miocene. The ecospectra are obtained using a ... [more ▼]

Based on ecospectra of 66 published carpofloras we study dynamics and evolution of Turgay vegetation in Western Siberia during the early Oligocene to earliest Miocene. The ecospectra are obtained using a Plant Functional Type (PFT) classification system comprising 26 herbaceous to arboreal PFTs. The carpofloras originate from seven floristic levels covering the time‐span from the Rupelian to early Aquitanian. Key elements of these levels are documented based on original collection materials. Although impacted by local edaphic conditions, the ecospectra can be interpreted in terms of changing vegetation. Our data show that warm temperate mesophytic, mixed conifer‐broad‐leaved deciduous forest assemblages persisted throughout the Oligocene and earliest Miocene in this core area of Turgai type vegetation. This is in line with comparatively stable climate conditions persisting in the studied time‐span, showing a minor temperature decline and coeval moderate increase in seasonality and precipitation. Concurrently, the reconstructed ecospectra contradict significant continental drying throughout the Oligocene and earliest Miocene. Spatial variability of the proportions of PFTs within the single floristic horizons primarily reflects local edaphic conditions. High diversities of PFTs characteristic for swamp vegetation are mainly confined to the early Oligocene and have a regional focus. Our results indicate that taxonomical diversity, particularly concerning mesic herbs and deciduous shrubs and trees, increased towards the end of the Oligocene. This increase in biodiversity probably can be attributed to an increase in rainfall and extension of terrestrial habitats after the final retreat of the Paratethys. [less ▲]

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See detailTree mortality submodels drive simulated long-term forest dynamics: assessing 15 models from the stand to global scale
Bugmann, H.; Seidl, R.; Hartig, F. et al

in Ecosphere (2019), 10(2),

Models are pivotal for assessing future forest dynamics under the impacts of changing climate and management practices, incorporating representations of tree growth, mortality, and regeneration ... [more ▼]

Models are pivotal for assessing future forest dynamics under the impacts of changing climate and management practices, incorporating representations of tree growth, mortality, and regeneration. Quantitative studies on the importance of mortality submodels are scarce. We evaluated 15 dynamic vegetation models (DVMs) regarding their sensitivity to different formulations of tree mortality under different degrees of climate change. The set of models comprised eight DVMs at the stand scale, three at the landscape scale, and four typically applied at the continental to global scale. Some incorporate empirically derived mortality models, and others are based on experimental data, whereas still others are based on theoretical reasoning. Each DVM was run with at least two alternative mortality submodels. Model behavior was evaluated against empirical time series data, and then, the models were subjected to different scenarios of climate change. Most DVMs matched empirical data quite well, irrespective of the mortality submodel that was used. However, mortality submodels that performed in a very similar manner against past data often led to sharply different trajectories of forest dynamics under future climate change. Most DVMs featured high sensitivity to the mortality submodel, with deviations of basal area and stem numbers on the order of 10–40% per century under current climate and 20–170% under climate change. The sensitivity of a given DVM to scenarios of climate change, however, was typically lower by a factor of two to three. We conclude that (1) mortality is one of the most uncertain processes when it comes to assessing forest response to climate change, and (2) more data and a better process understanding of tree mortality are needed to improve the robustness of simulated future forest dynamics. Our study highlights that comparing several alternative mortality formulations in DVMs provides valuable insights into the effects of process uncertainties on simulated future forest dynamics. © 2019 The Authors. [less ▲]

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See detailState-of-the-art global models underestimate impacts from climate extremes
Schewe, J.; Gosling, S. N.; Reyer, C. et al

in Nature Communications (2019), 10(1), 1005

Global impact models represent process-level understanding of how natural and human systems may be affected by climate change. Their projections are used in integrated assessments of climate change. Here ... [more ▼]

Global impact models represent process-level understanding of how natural and human systems may be affected by climate change. Their projections are used in integrated assessments of climate change. Here we test, for the first time, systematically across many important systems, how well such impact models capture the impacts of extreme climate conditions. Using the 2003 European heat wave and drought as a historical analogue for comparable events in the future, we find that a majority of models underestimate the extremeness of impacts in important sectors such as agriculture, terrestrial ecosystems, and heat-related human mortality, while impacts on water resources and hydropower are overestimated in some river basins; and the spread across models is often large. This has important implications for economic assessments of climate change impacts that rely on these models. It also means that societal risks from future extreme events may be greater than previously thought. © 2019, The Author(s). [less ▲]

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See detailSimulating last glacial and postglacial distributions of African tropical trees with a dynamic vegetation model.
Dury, Marie ULiege; Henrot, Alexandra-Jane ULiege; Lézine, Anne-Marie et al

Conference (2018, August 16)

Climate change and human pressure threaten species richness of African tropical forests. Understanding how the past climate changes have shaped the current distribution and composition of African ... [more ▼]

Climate change and human pressure threaten species richness of African tropical forests. Understanding how the past climate changes have shaped the current distribution and composition of African rainforests can certainly help to the ecosystem conservation in the future. This topic is addressed in the framework of the multi-disciplinary AFRIFORD project (Genetic and palaeoecological signatures of African rainforest dynamics: pre-adapted to change?, http://www.ulb.ac.be/facs/sciences/afriford/). In parallel to genetic and palynological analyses, the CARAIB dynamic vegetation model is applied at the level of African tropical plant species to simulate change in their distributions from the Last Glacial Maximum (21,000 years BP) to the present in sub-Saharan Africa. We prepared a set of about a hundred species, mostly composed of tropical tree species (evergreen/deciduous, cool/warm taxa) for which we compiled observed occurrence data (e.g.., RAINBIO database), determined climatic requirements and gathered some specific traits (e.g., TRY database). From LGM to present time, the vegetation model is forced with the 1-kyr snapshot outputs of the HadCM3 climate model. Statistically downscaled at a spatial resolution of 0.5°, we only kept modelled past anomalies that we added to the GSWP3 (20 CR) climate data chosen as the reference for the historical period. Sub-Saharan simulations are performed with CARAIB forced by these climatic projections to simulate the net primary productivity of the species over time and space. We analyse the modelled changes in tropical forest composition and extension as well as in the distribution of individual species whose glacial refugia and postglacial dynamics remain poorly known. [less ▲]

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See detailAre the climatic ranges of plant species impacted by atmospheric CO2 ? An attempt of quantification with a dynamic vegetation model
François, Louis ULiege; Henrot, Alexandra-Jane ULiege; Dury, Marie ULiege et al

Conference (2018, August 16)

The observed present-day climatic ranges of plant species are frequently used by palaeobotanists and palynologists to reconstruct the climate evolution in the past. This is, for instance, the case of the ... [more ▼]

The observed present-day climatic ranges of plant species are frequently used by palaeobotanists and palynologists to reconstruct the climate evolution in the past. This is, for instance, the case of the widely used “Coexistence Approach” method, which has provided a wealth of palaeoclimatic data on many periods of the Neogene. Such vegetation-based palaeoclimate reconstruction methods rest on the uniformitarian assumption that the climatic tolerances of plant species, or the way their establishment and growth respond to climate parameters, have not changed markedly over time. This hypothesis can be questioned, because climatic tolerances and growth of plant species may depend on many factors likely to change over time. A first example is that other abiotic and biotic factors allowing the plant presence have probably changed in the course of time. Another example is genetic evolution that may affect climate resistance and end up to some adaptation of the populations as climate is changing. Atmospheric CO2 may also modify the plant response. It is not accounted for in the vegetation-based palaeoclimatic reconstruction methods, but may alter the tolerance of plant species to aridity through stomatal closure or stomatal density changes. Moreover, a rise of atmospheric CO2 stimulates photosynthesis through the well-known CO2 fertilisation effect. How far this effect impacts plant growth and how long it can persist is still much debated in the scientific community. It likely depends on the nutrient abundance in the soils. However, if CO2 stimulates growth, it will also facilitate the colonisation of extreme environments by plant species. Indeed, their growth rate between two successive extreme climatic events will be enhanced and, so, the accumulated biomass will be larger and the likelihood to find their signature in the palaeovegetation records will increase. In this contribution, we attempt to quantify this impact of CO2 on the climatic ranges of plant species by using the CARAIB dynamic vegetation model. This dynamic vegetation model can be run at the species level. We use a set of tree species from various climatic zones over different continents, for which the model has proved a good ability to simulate the present-day distribution. The model is run for different levels of atmospheric CO2, but with exactly the same climatic inputs. The simulated tree species distributions versus different climate variables (mean annual temperature, coldest month temperature, mean annual precipitation, precipitation of the driest month, etc) are then analysed and compared among the different CO2 configurations. [less ▲]

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See detailSimulating seed dispersal to reproduce past dynamics and distribution of African tropical trees.
Dury, Marie ULiege; Hardy, Olivier; Migliore, Jérémy et al

Poster (2018, March 28)

Climate change and human pressure threaten species richness of African tropical forests. Understanding how the past climate changes have shaped the current distribution and composition of African ... [more ▼]

Climate change and human pressure threaten species richness of African tropical forests. Understanding how the past climate changes have shaped the current distribution and composition of African rainforests can certainly help to the ecosystem conservation in the future. In the framework of the multi-disciplinary AFRIFORD project (Genetic and palaeoecological signatures of African rainforest dynamics: pre-adapted to change?, http://www.ulb.ac.be/facs/sciences/afriford/), this kind of questions is addressed. The CARAIB dynamic vegetation model is applied at the level of representative African tropical tree species to reconstruct their past and present distributions in equatorial Africa. To reproduce fully population dynamics, the results of the vegetation model are combined with a seed dispersal model. At first, we simulate with the CARAIB DVM the changes over time in the potential distribution of the tree species studied in AFRIFORD taking competition between species into account. From Last Glacial Maximum (LGM) to present time, the vegetation model is forced with the 1-kyr snapshot outputs of the HadCM3 climate model, statistically downscaled at a spatial resolution of 0.5° and bias-corrected. The calculated distributions are essentially in equilibrium with climate, except for small delay times associated with biomass growth. These distributions are also compared directly with the potential (no dispersal limitation either) distributions obtained from species distribution modelling (MaxENT) for the same set of tree species and with the same climate forcing. Then, to simulate tree species under limitation by both climate and seed dispersal, the dispersal module is run transiently on a sub-grid at 100 m resolution to reproduce species dynamics over the 20,000 years from their LGM refugia (simulated by the DVM). The dispersal capacities are dependent on species productivity and survival simulated by the DVM for each1-kyr snapshot. The modelled dispersal distances are compared to genetic-based dispersal distances estimated in the project. [less ▲]

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See detailDistribution of Podocarpus latifolius/milanjianus from the Last Glacial Maximum to 2100 in Africa with the dynamic vegetation model CARAIB.
Dury, Marie ULiege; Henrot, Alexandra-Jane ULiege; Lézine, Anne-Marie et al

Conference (2018, March 27)

Podocarpus latifolius/milanjianus (same species according to genetics) is an endemic African species with populations in the western, eastern and southern parts of the continent. The current global ... [more ▼]

Podocarpus latifolius/milanjianus (same species according to genetics) is an endemic African species with populations in the western, eastern and southern parts of the continent. The current global warming threatens the conservation of the relict patches of this mountain evergreen species. During the Last Glacial Maximum (LGM), the species was certainly more largely distributed and present at lower elevations than today according to pollen data. At the beginning of the Holocene, Podocarpus moved upwards due to warmer conditions. The size of the populations might have collapsed abruptly at the end of the ”African Humid Period” at ca. 3,000 BP. Besides this general evolution, the palaeo-distribution of Podocarpus remains relatively unknown. The origin and connections between the eastern, southern and western Podocarpus forests are still not understood. In the framework of two related projects, AFRIFORD and VULPES, we use the CARAIB dynamic vegetation model, in parallel to genetic and palynologic analyses, to simulate the past and future dynamics of Podocarpus and to understand its current distribution. Projections of the HadCM3 climate model are used to reproduce climatic conditions in Africa from LGM (21,000 BP) to present time with a temporal resolution of 1 kyr. For the future (until 2100), several IPCC CMIP5 climate scenarios have been selected according to the quality of their reconstructed climate (temperature and precipitation) over sub-Saharan Africa for historical period. After interpolation to a 0.5° regular grid, we kept only past/future anomalies that we added to the GSWP3 (20 CR) climate data chosen as the reference for the historical period. Sub-continental simulations are performed with CARAIB forced by these climatic projections to simulate the net primary productivity of Podocarpus over time and space. In addition, CARAIB simulations are performed at higher resolution over a restricted region in southwestern Cameroon to identify potential microrefugia. [less ▲]

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See detailRefining species traits in a dynamic vegetation model to project the impacts of climate change on tropical trees in Central Africa
Dury, Marie ULiege; Mertens, L.; Fayolle, Adeline ULiege et al

in Forests (2018), 9(11),

African tropical ecosystems and the services they provide to human society suffer from an increasing combined pressure of land use and climate change. How individual tropical tree species respond to ... [more ▼]

African tropical ecosystems and the services they provide to human society suffer from an increasing combined pressure of land use and climate change. How individual tropical tree species respond to climate change remains relatively unknown. In this study, we refined the species characterization in the CARAIB (CARbon Assimilation In the Biosphere) dynamic vegetation model by replacing plant functional type morpho-physiological traits by species-specific traits. We focus on 12 tropical tree species selected for their importance in both the plant community and human society. We used CARAIB to simulate the current species net primary productivity (NPP), biomass and potential distribution and their changes in the future. Our results indicate that the use of species-specific traits does not necessarily result in an increase of predicted current NPPs. The model projections for the end of the century highlight the large uncertainties in the future of African tropical species. Projected changes in species distribution vary greatly with the general circulation model (GCM) and, to a lesser extent, with the concentration pathway. The question about long-term plant response to increasing CO2 concentrations also leads to contrasting results. In absence of fertilization effect, species are exposed to climate change and might lose 25% of their current distribution under RCP8.5 (12.5% under RCP4.5), considering all the species and climatic scenarios. The vegetation model projects a mean biomass loss of -21.2% under RCP4.5 and -34.5% under RCP8.5. Potential range expansions, unpredictable due to migration limitations, are too limited for offsetting range contraction. By contrast, if the long-term species response to increasing [CO2] is positive, the range reduction is limited to 5%. However, despite a mean biomass increase of 12.2%, a positive CO2 feedback might not prevent tree dieback. Our analysis confirms that species will respond differently to new climatic and atmospheric conditions, which may induce new competition dynamics in the ecosystem and affect ecosystem services. © 2018 by the authors. [less ▲]

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See detailEvaluation by prediction of the natural range shrinkage of Quercus ilex L. in Eastern Algeria
Tabet, Slimane; Belhemra, Mohammed; François, Louis ULiege et al

in Forestist (2018), 68

This study focuses on the evaluation by prediction of the spatial distribution of Quercus ilex. L in its natural range in Eastern Algeria. The maximum entropy method has allowed the modelling of the ... [more ▼]

This study focuses on the evaluation by prediction of the spatial distribution of Quercus ilex. L in its natural range in Eastern Algeria. The maximum entropy method has allowed the modelling of the species potentially favourable areas under environmental conditions linking the spatial occurrence and the environmental conditions. Three explanatory parameter groups were used for modelling: i) Edaphic variables, ii) Variables related to topography, iii) Climatic variables. The established predictions demonstrate that over the horizons 2050 and 2070, we will lose 125000 and 147000 hectares respectively. It would seem that the most favourable areas for Quercus ilex would extend between elevations of 1430 meters for 2050 and reach by 2070, 1650 meters. The performance of the used model has been confirmed by the value of AUC which is 0,929. The high elevations especially those of the Saharian Atlas will offer the climatic refuges. These results represent a decision support tool for the best strategy of sensibilization and planning for the holm oak conservation. [less ▲]

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See detailEvaluating changes of biomass in global vegetation models: the role of turnover fluctuations and ENSO events
Cantú, Anselmo García; Frieler, Katja; Reyer, Christopher P O et al

in Environmental Research Letters (2018)

This paper evaluates the ability of eight global vegetation models to reproduce recent trends and inter-annual variability of biomass in natural terrestrial ecosystems. For the purpose of this evaluation ... [more ▼]

This paper evaluates the ability of eight global vegetation models to reproduce recent trends and inter-annual variability of biomass in natural terrestrial ecosystems. For the purpose of this evaluation, the simulated trajectories of biomass are expressed in terms of the relative rate of change in biomass (RRB), defined as the deviation of the actual rate of biomass turnover from its equilibrium counterpart. Cumulative changes in RRB explain long-term changes in biomass pools. RRB simulated by the global vegetation models is compared with its observational equivalent, derived from vegetation optical depth reconstructions of above-ground biomass (AGB) over the period 1993–2010. According to the RRB analysis, the rate of global biomass growth described by the ensemble of simulations substantially exceeds the observation. The observed fluctuations of global RRB are significantly correlated with El Niño Southern Oscillation events (ENSO), but only some of the simulations reproduce this correlation. However, the ENSO sensitivity of RRB in the tropics is not significant in the observation, while it is in some of the simulations. This mismatch points to an important limitation of the observed AGB reconstruction to capture biomass variations in tropical forests. Important discrepancies in RRB were also identified at the regional scale, in the tropical forests of Amazonia and Central Africa, as well as in the boreal forests of north-western America, western and central Siberia. In each of these regions, the RRBs derived from the simulations were analyzed in connection with underlying differences in net primary productivity and biomass turnover rate ̶as a basis for exploring in how far differences in simulated changes in biomass are attributed to the response of the carbon uptake to CO2 increments, as well as to the model representation of factors affecting the rates of mortality and turnover of foliage and roots. Overall, our findings stress the usefulness of using RRB to evaluate complex vegetation models and highlight the importance of conducting further evaluations of both the actual rate of biomass turnover and its equilibrium counterpart, with special focus on their background values and sources of variation. In turn, this task would require the availability of more accurate multi-year observational data of biomass and net primary productivity for natural ecosystems, as well as detailed and updated information on land-cover classification. [less ▲]

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See detailGlobal crop production: adaptation options to temperature increase
Minoli, Sara; Elliott, Joshua; Ruane, Alex C et al

Poster (2018)

Climate change is already and will continue affecting the productivity of agricultural systems, therefore demanding for adaptation strategies to avoid production losses. Due to the complexity and ... [more ▼]

Climate change is already and will continue affecting the productivity of agricultural systems, therefore demanding for adaptation strategies to avoid production losses. Due to the complexity and heterogeneity of crop-climate-soil systems, adaptation options are mostly implemented and evaluated locally. Nevertheless, global-scale estimates are needed because e.g. the efficiency of adaptation measures needs to be discussed in the context of costs and opportunities elsewhere. Global gridded crop models (GGCMs) can be informative at both local and larger scales by consistently simulating the entire global crop-land while accounting at the same time for local conditions. Here we present the first systematic study on cropping systems adaptation to temperature increase based on a GGCMs ensemble sensitivity analysis. The models consistently implemented two management options that can alleviate impacts of temperature increase on major grain crops: first an adoption of new cultivars to maintain the original growing period (a measure to counteract accelerated crop phenology) and then a full irrigation (with the aim of avoiding increased water stress due to increased atmospheric vapor pressure deficit (VPD) under warming). We assess the effectiveness of these two options, as well as their combination, in avoiding yield losses of four major crops (maize, wheat, rice and soybean). First results show that, at the global aggregation, irrigation and the unaltered growing period both allow for increasing yields under most warming scenarios, and that the most positive effects occur when these strategies are combined. We also study how adaptation effectiveness varies across regions of the global crop land. In temperate regions a cultivar shift typically has positive effects by reducing yield losses and often even leads to fully maintaining or exceeding the baseline yield levels across various levels of warming. On the other hand, in warmer areas, such as the tropics, this strategy only shows limited effects, even when combined with irrigation and already at moderate warming levels. This suggests that in such environment temperature is already a strong limiting factor that cannot be alleviated by altered crop phenology. This poses a challenge to identify and model alternative adaptation strategies. Irrigation typically helps to increase yields in water-scarce growing environments, but this is also true for most baseline conditions. Irrigation becomes a true adaptation measure only if the yield increase is larger under warming than under baseline conditions. This can e.g. occur in regions where the additional warming leads to substantial increases in VPD. [less ▲]

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See detailClassifying multi-model wheat yield impact response surfaces showing sensitivity to temperature and precipitation change
Fronzek, Stefan; Pirttioja, Nina; Carter, Timothy R. et al

in Agricultural Systems (2018), 159

Crop growth simulation models can differ greatly in their treatment of key processes and hence in their response to environmental conditions. Here, we used an ensemble of 26 process-based wheat models ... [more ▼]

Crop growth simulation models can differ greatly in their treatment of key processes and hence in their response to environmental conditions. Here, we used an ensemble of 26 process-based wheat models applied at sites across a European transect to compare their sensitivity to changes in temperature (−2 to +9°C) and precipitation (−50 to +50%). Model results were analysed by plotting them as impact response surfaces (IRSs), classifying the IRS patterns of individual model simulations, describing these classes and analysing factors that may explain the major differences in model responses. The model ensemble was used to simulate yields of winter and spring wheat at four sites in Finland, Germany and Spain. Results were plotted as IRSs that show changes in yields relative to the baseline with respect to temperature and precipitation. IRSs of 30-year means and selected extreme years were classified using two approaches describing their pattern. The expert diagnostic approach (EDA) combines two aspects of IRS patterns: location of the maximum yield (nine classes) and strength of the yield response with respect to climate (four classes), resulting in a total of 36 combined classes defined using criteria pre-specified by experts. The statistical diagnostic approach (SDA) groups IRSs by comparing their pattern and magnitude, without attempting to interpret these features. It applies a hierarchical clustering method, grouping response patterns using a distance metric that combines the spatial correlation and Euclidian distance between IRS pairs. The two approaches were used to investigate whether different patterns of yield response could be related to different properties of the crop models, specifically their genealogy, calibration and process description. Although no single model property across a large model ensemble was found to explain the integrated yield response to temperature and precipitation perturbations, the application of the EDA and SDA approaches revealed their capability to distinguish: (i) stronger yield responses to precipitation for winter wheat than spring wheat; (ii) differing strengths of response to climate changes for years with anomalous weather conditions compared to period-average conditions; (iii) the influence of site conditions on yield patterns; (iv) similarities in IRS patterns among models with related genealogy; (v) similarities in IRS patterns for models with simpler process descriptions of root growth and water uptake compared to those with more complex descriptions; and (vi) a closer correspondence of IRS patterns in models using partitioning schemes to represent yield formation than in those using a harvest index. Such results can inform future crop modelling studies that seek to exploit the diversity of multi-model ensembles, by distinguishing ensemble members that span a wide range of responses as well as those that display implausible behaviour or strong mutual similarities. [less ▲]

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See detailHigh-resolution simulations of natural and agricultural ecosystems over Belgium with the CARAIB Dynamic Vegetation Model
Jacquemin, Ingrid ULiege; Dury, Marie ULiege; Henrot, Alexandra-Jane ULiege et al

Conference (2017, November 17)

CARAIB (for CARbon Assimilation In the Biosphere) is a state-of-the-art dynamic vegetation model (DVM), initially designed to study the role of the vegetation in the global carbon cycle and the vegetation ... [more ▼]

CARAIB (for CARbon Assimilation In the Biosphere) is a state-of-the-art dynamic vegetation model (DVM), initially designed to study the role of the vegetation in the global carbon cycle and the vegetation behavior as a function of climate and soil. Motivated by the requirements of ecosystem management and land use planning studies, CARAIB was recently improved so as to deal with both natural and agricultural ecosystems and at a high resolution of 1km over Belgium. A new module, for crops and meadows, was added in the model, which deals with the specific processes (phenology) and management (sowing, harvesting,…) of these ecosystems. The spatial and temporal validation was carried out with different data sources : agricultural statistics, eddy-covariance site, field measurements,… The addition of the crop module has led to the improvement of the surface scheme, from now on including dynamic land use and land cover information. As well as describes the evolution of physical and biological processes, CARAIB has become an interesting tool to assess the sustainability under climate change of the ecological systems, in particular by the approach of the ecosystem goods and services. Indeed, if some model outputs can be directly read as quantitative indicators of ecosystem services (e.g. carbon sequestration), we have translated some of them to get, e.g., the crop yield (from net primary productivity) or an estimation of the soil erosion for simulation at the parcel level (from runoff and parcels characteristics). But whether an ecosystem services or land use planning studies, the crucial point for CARAIB is the landscape dynamics, which is not considered by the model, in the absence of anthropogenic, economic and societal factors in the system. In order to overcome this lack, CARAIB is now coupled with an agent-based model (ABM), to compose a land surface dynamics (LSD) module. The productivity and growth of natural and managed vegetation is given by the DVM to the ABM, which determines the shifts in land use and land cover. The LSD module is able to represent the mutual interactions between ecological and socio-economic systems and thus, to assess the sustainability of the different climate and socio-economic scenarios tested. [less ▲]

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See detailCombining multiple statistical methods to evaluate the performance of process-based vegetation models across three forest stands
Horemans, Joanna A.; Henrot, Alexandra-Jane ULiege; Delire, Christine et al

in Central European Forestry Journal (2017)

Process-based vegetation models are crucial tools to better understand biosphere-atmosphere exchanges and ecophysiological responses to climate change. In this contribution the performance of two global ... [more ▼]

Process-based vegetation models are crucial tools to better understand biosphere-atmosphere exchanges and ecophysiological responses to climate change. In this contribution the performance of two global dynamic vegetation models, i.e. CARAIB and ISBACC, and one stand-scale forest model, i.e. 4C, was compared to long-term observed net ecosystem carbon exchange (NEE) time series from eddy covariance monitoring stations at three old-grown European beech (Fagus sylvatica L.) forest stands. Residual analysis, wavelet analysis and singular spectrum analysis were used beside conventional scalar statistical measures to assess model performance with the aim of defining future targets for model improvement. We found that the most important errors for all three models occurred at the edges of the observed NEE distribution and the model errors were correlated with environmental variables on a daily scale. These observations point to possible projection issues under more extreme future climate conditions. Recurrent patterns in the residuals over the course of the year were linked to the approach to simulate phenology and physiological evolution during leaf development and senescence. Substantial model errors occurred on the multi-annual time scale, possibly caused by the lack of inclusion of management actions and disturbances. Other crucial processes defined were the forest structure and the vertical light partitioning through the canopy. Further, model errors were shown not to be transmitted from one time scale to another. We proved that models should be evaluated across multiple sites, preferably using multiple evaluation methods, to identify processes that request reconsideration. [less ▲]

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See detailHow do individual species and Plant Functional Type responses to environmental change differ in Dynamic Vegetation Models? - A forest stand analysis
Dury, Marie ULiege; Henrot, Alexandra-Jane ULiege; Jacquemin, Ingrid ULiege et al

Poster (2017, October 09)

Originally dedicated to simulate vegetation at the global scale, dynamic (global) vegetation models (D(G)VMs) classify vegetation into Plant Functional Types (PFTs) to represent the largest set of plant ... [more ▼]

Originally dedicated to simulate vegetation at the global scale, dynamic (global) vegetation models (D(G)VMs) classify vegetation into Plant Functional Types (PFTs) to represent the largest set of plant species. PFTs are clusters of species that share common morphological and physiological traits. However, PFT classification becomes surely too coarse to reflect the large diversity in plant species responses to climate and environmental changes, a critical point for biodiversity questions. Thus, some efforts focus now on applying DVMs at the species level refining the definition of morphophysiological parameters from initial PFT traits to specific traits collected or found in trait databases. What are the effects of using species-specific parameters? Do dynamic vegetation models better reproduce historical forest growth and mortality observed in monitored stands? How will individual species respond to future climate compared to PFTs? To study these questions, we used two process-based dynamic vegetation models CARAIB (Dury et al., 2011) as well as LPJ-GUESS (Smith et al., 2001), and compared their outputs. CARAIB has been previously adapted to model a set of 40 European tree species, differentiated by their specific traits, proper climatic requirements and tolerances. LPJ-GUESS features a detailed representation of climate sensitive tree species dynamics, resource competition and canopy structure (Hickler et al., 2012). The respective tree species are distinguished by taking differences in phenology, allometry and bioclimatic limits into account. Model simulations were performed in accordance with the experimental protocol of the COST Action PROFOUND (“Towards robust projections of European forests under climate change”) for several European forest stands selected in the project. We particularly focused on Fagus sylvatica stand in Sorø (Denmark), Picea abies stand in Solling (Germany) and Pinus sylvestris (and Picea abies) stands in Hyytiala (Finland). The experiments include site-specific soil characteristics, management practices (planting, thinning and harvest) and climate conditions. For the historical period (from planting year to 2014), besides local observations, simulations were also run with the original (0.5-degree spatial resolution) and locally bias-corrected (LBC) ISIMIP2B outputs of global climate models for testing the reliance of DVM results to the spatial resolution of climatic inputs. For the future period (2005-2100), vegetation models were driven by the ISIMIP2B climates under different Representative Concentration Pathways. The simulations at the PFT level were performed following the same protocol replacing the locally present species by their representative PFTs. The carbon and water fluxes obtained from the different experiments carried out with the two DVMs were compared with eddy-covariance data from each site. [less ▲]

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See detailÉvaluation de la capacité du Modèle Atmosphérique Régional (MAR) à simuler la saison des pluies en Afrique Intertropicale
Doutreloup, Sébastien ULiege; Wyard, Coraline ULiege; Belleflamme, Alexandre ULiege et al

in Dahech, Salem; Charfi, Sami (Eds.) Actes du XXXe colloque de l'Association Internationale de Climatologie : CLIMAT, VILLE ET ENVIRONNEMENT (2017, July)

In Intertropical Africa, climate is essentially characterized by the amount of precipitation and its annual regime. These precipitations and their evolution during the period 1970-1999 are simulated ... [more ▼]

In Intertropical Africa, climate is essentially characterized by the amount of precipitation and its annual regime. These precipitations and their evolution during the period 1970-1999 are simulated thanks to the Regional Atmospheric Model (MAR), developed at the ULg, and forced by the NCEP1 reanalyses and by the outputs of three global models (GCM) of the CMIP5 database. These MAR simulations are compared to the gridded data of the Climate Research Unit (CRU). It is clear from our investigations that the simulation of the MAR model forced by the NCEP1 reanalyses is better reproducing the quantities as well as the annual rainfall regime in the semi-arid regions than in equatorial regions. On the other hand, simulations of the MAR forced by the outputs of the GCMs are globally unsatisfactory throughout the intertropical domain in terms of quantities as well as the seasonality of precipitation. [less ▲]

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