Analyzing the Ecosystem Carbon Dynamics of Four European Coniferous Forests Using a Biogeochemistry Model (original) (raw)
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Agricultural and forest …, 2006
The effects of climate changes on carbon and water fluxes are quantified using a physiologically multi-layer, process-based model containing a carbon allocation model and coupled with a soil model (CASTANEA). The model is first evaluated on four EUROFLUX sites using eddy covariance data, which provide estimates of carbon and water fluxes at the ecosystem scale. It correctly reproduces the diurnal fluxes and the seasonal pattern. Thereafter simulations were conducted on six French forest ecosystems representative of three climatic areas (oceanic, continental and Mediterranean areas) dominated by deciduous species (Fagus sylvatica, Quercus robur), coniferous species (Pinus pinaster, Pinus sylvestris) or sclerophyllous evergreen species (Quercus ilex). The model is driven by the results of a meteorological model (ARPEGE) following the B2 scenario of IPCC. From 1960 to 2100, the average temperature increases by 3.1 °C (30%) and the rainfall during summer decreases by 68 mm (−27%). For all the sites, between the two periods, the simulations predict on average a gross primary production (GPP) increase of 513 g(C) m−2 (+38%). This increase is relatively steep until 2020, followed by a slowing down of the GPP rise due to an increase of the effect of water stress. Contrary to GPP, the ecosystem respiration (Reco) raises at a constant rate (350 g(C) m−2 i.e. 31% from 1960 to 2100). The dynamics of the net ecosystem productivity (GPP minus Reco) is the consequence of the effect on both GPP and Reco and differs per site. The ecosystems always remain carbon sinks; however the sink strength globally decreases for coniferous (−8%), increases for sclerophyllous evergreen (+34%) and strongly increases for deciduous forest (+67%) that largely benefits by the lengthening of the foliated period. The separately quantified effects of the main variables (temperature, length of foliated season, CO2 fertilization, drought effect), show that the magnitude of these effects depends on the species and the climatic zone.
Global Change Biology, 2005
Process-based models can be classified into: (a) terrestrial biogeochemical models (TBMs), which simulate fluxes of carbon, water and nitrogen coupled within terrestrial ecosystems, and (b) dynamic global vegetation models (DGVMs), which further couple these processes interactively with changes in slow ecosystem processes depending on resource competition, establishment, growth and mortality of different vegetation types. In this study, four models – RHESSys, GOTILWA+, LPJ-GUESS and ORCHIDEE – representing both modelling approaches were compared and evaluated against benchmarks provided by eddy-covariance measurements of carbon and water fluxes at 15 forest sites within the EUROFLUX project. Overall, model-measurement agreement varied greatly among sites. Both modelling approaches have somewhat different strengths, but there was no model among those tested that universally performed well on the two variables evaluated. Small biases and errors suggest that ORCHIDEE and GOTILWA+ performed better in simulating carbon fluxes while LPJ-GUESS and RHESSys did a better job in simulating water fluxes. In general, the models can be considered as useful tools for studies of climate change impacts on carbon and water cycling in forests. However, the various sources of variation among models simulations and between models simulations and observed data described in this study place some constraints on the results and to some extent reduce their reliability. For example, at most sites in the Mediterranean region all models generally performed poorly most likely because of problems in the representation of water stress effects on both carbon uptake by photosynthesis and carbon release by heterotrophic respiration (Rh).The use of flux data as a means of assessing key processes in models of this type is an important approach to improving model performance. Our results show that the models have value but that further model development is necessary with regard to the representation of the some of the key ecosystem processes.
Carbon balance of coniferous forests growing in contrasting climates: Model-based analysis
2005
Forest carbon exchange contributes significantly to the global carbon balance and is therefore being monitored around the world, most notably using eddy covariance technology. In order to extrapolate from these measurements, we need to understand why carbon balance (or net ecosystem production, NEP) differs among forests. Here, we use a detailed model of forest carbon exchange applied to three coniferous European forests with differing NEP to pinpoint reasons for the differences among these sites. The model was parameterised using extensive ecophysiological data obtained at each site. These data gave evidence of major differences among sites in climate, leaf physiology, respiring biomass, leaf area index, and soil and biomass respiration rates. The model was compared with eddy covariance data and found to satisfactorily simulate carbon exchange by each forest. Simulations were then run which interchanged canopy structure, physiology and meteorology among sites, allowing us to quantify the contribution of each factor to the inter-site differences in gross primary productivity (GPP), ecosystem respiration (RE) and NEP. The most important factor was the difference in respiration rates, particularly soil respiration rates, among sites. Climate was also very important, with differences in incident photosynthetically active radiation (PAR) affecting GPP and differences in temperature affecting both GPP and RE. Effects of leaf area index, respiring biomass and leaf physiology on NEP were secondary, but still substantial. The work provides detailed quantitative evidence of the major factors causing differences in NEP among coniferous forests. #
The effects of climate changes on carbon and water fluxes are quantified using a physiologically multi-layer, process-based model containing a carbon allocation model and coupled with a soil model (CASTANEA). The model is first evaluated on four EUROFLUX sites using eddy covariance data, which provide estimates of carbon and water fluxes at the ecosystem scale. It correctly reproduces the diurnal fluxes and the seasonal pattern. Thereafter simulations were conducted on six French forest ecosystems representative of three climatic areas (oceanic, continental and Mediterranean areas) dominated by deciduous species (Fagus sylvatica, Quercus robur), coniferous species (Pinus pinaster, Pinus sylvestris) or sclerophyllous evergreen species (Quercus ilex). The model is driven by the results of a meteorological model (ARPEGE) following the B2 scenario of IPCC. From 1960 to 2100, the average temperature increases by 3.1 8C (30%) and the rainfall during summer decreases by 68 mm (À27%). For all the sites, between the two periods, the simulations predict on average a gross primary production (GPP) increase of 513 g(C) m À2 (+38%). This increase is relatively steep until 2020, followed by a slowing down of the GPP rise due to an increase of the effect of water stress. Contrary to GPP, the ecosystem respiration (R eco ) raises at a constant rate (350 g(C) m À2 i.e. 31% from 1960 to 2100). The dynamics of the net ecosystem productivity (GPP minus R eco ) is the consequence of the effect on both GPP and R eco and differs per site. The ecosystems always remain carbon sinks; however the sink strength globally decreases for coniferous (À8%), increases for sclerophyllous evergreen (+34%) and strongly increases for deciduous forest (+67%) that largely benefits by the lengthening of the foliated period. The separately quantified effects of the main variables (temperature, length of foliated season, CO 2 fertilization, drought effect), show that the magnitude of these effects depends on the species and the climatic zone. #
Geoscientific Model Development, 2017
How carbon (C) is allocated to different plant tissues (leaves, stem, and roots) determines how long C remains in plant biomass and thus remains a central challenge for understanding the global C cycle. We used a diverse set of observations (AmeriFlux eddy covariance tower observations, biomass estimates from tree-ring data, and leaf area index (LAI) measurements) to compare C fluxes, pools, and LAI data with those predicted by a land surface model (LSM), the Community Land Model (CLM4.5). We ran CLM4.5 for nine temperate (including evergreen and deciduous) forests in North America between 1980 and 2013 using four different C allocation schemes: i. dynamic C allocation scheme (named "D-CLM4.5") with one dynamic allometric parameter, which allocates C to the stem and leaves to vary in time as a function of annual net primary production (NPP); ii. an alternative dynamic C allocation scheme (named "D-Litton"), where, similar to (i), C allocation is a dynamic function of annual NPP, but unlike (i) includes two dynamic allometric parameters involving allocation to leaves, stem, and coarse roots; iii.-iv. a fixed C allocation scheme with two variants, one representative of observations in evergreen (named "F-Published by Copernicus Publications on behalf of the European Geosciences Union.
2020
The mechanistic model GO+ describes the functioning and growth of managed forests based upon biophysical and biogeochemical processes. The biophysical and biogeochemical processes included are modelled using standard formulations of radiative transfer, convective heat exchange, evapotranspiration, photosynthesis, respiration, plant phenology, growth and mortality, biomass nutrient content, and soil carbon dynamics. The forest ecosystem is modelled as three layers, namely the tree overstorey, understorey and soil. The vegetation layers include stems, branches and foliage and are partitioned dynamically between sunlit and shaded fractions. The soil carbon submodel is an adaption of the Roth-C model to simulate the impact of forest operations. The model runs at an hourly time step. It represents a forest stand covering typically 1 ha and can be straightforwardly upscaled across gridded data at regional, country or continental levels. GO+ accounts for both the immediate and long-term impacts of forest operations on energy, water and carbon exchanges within the soil-vegetation-atmosphere continuum. It includes exhaustive and versatile descriptions of management operations (soil preparation, regeneration, vegetation control, selective thinning, clear-cutting, coppicing, etc.), thus permitting the effects of a wide variety of forest management strategies to be estimated: from close to nature to intensive. This paper examines the sensitivity of the model to its main parameters and estimates how errors in parameter values are propagated into the predicted values of its main output variables.The sensitivity analysis demonstrates an interaction between the sensitivity of variables, with the climate and soil hydraulic properties being dominant under dry conditions but the leaf biochemical properties being most influential with wet soil. The sensitivity profile of the model changes from short to long timescales due to the cumulative effects of the fluxes of carbon, energy and water on the stand growth and canopy structure. Apart from a few specific cases, the model simulations are close to the values of the observations of atmospheric exchanges, tree growth, and soil carbon and water stock changes monitored over Douglas fir, European beech Published by Copernicus Publications on behalf of the European Geosciences Union. 5974 V. Moreaux et al.: GO+v3.0 forest model and pine forests of different ages. We also illustrate the capacity of the GO+ model to simulate the provision of key ecosystem services, such as the long-term storage of carbon in biomass and soil under various management and climate scenarios.
Modelling carbon and water cycles in a beech forest
Ecological Modelling, 2005
A forest ecosystem model (CASTANEA) simulating the carbon balance (canopy photosynthesis, autotrophic and heterotrophic respirations, net ecosystem exchange, wood and root growth) and the water cycle (transpiration, soil evaporation, interception, drainage and soil water status) is tested with data from a young beech forest (Fagus sylvatica L.). For this purpose, the model validity is assessed by comparison between net CO 2 and H 2 O fluxes simulated and measured by the eddy flux technique over one year. In addition, most of the sub-models describing the processes mentioned above are tested using independent measurements from the same forest stand: tree growth, branch photosynthesis, wood and soil respirations, sap flow and soil water content. Most of the input parameters (both weather and plant characteristics) are measured in the same experimental site (i.e. Hesse forest) independently of the validation dataset (none has been fitted to match the output data, except rainfall interception parameters); some are from other beech sites or from literature. Concerning the radiative transfer, the model reproduces the measured exponential PAR extinction and provides a good estimate of the net radiative budget, except during winter. At the branch scale, simulated photosynthesis and transpiration of sun-leaves are close to the measurements. We show also, using model simulations, that the seasonal decrease of measured net photosynthesis at the branch level could be explained by a decrease in leaf nitrogen content during the leafy season. At stand scale, a good correlation was obtained between simulated and observed fluxes both on a half-hourly basis and on a daily basis. Except at the end of the leafy season, the model reproduces reasonably well the seasonal pattern of both CO 2 and H 2 O fluxes. Finally, even if there are some discrepancies between model estimations and fluxes measured at stand scale by eddy covariance, the model simulates properly both annual carbon and water balances when compared with the sum of the measured local fluxes. The remaining differences question the scaling up process when building such a model and the spatial footprint of eddy fluxes measurements.
Ecological Modelling, 1994
In this publication an approach is described to model the Net Carbon Exchange (NCE) between the vegetated surface-atmosphere interface of a deciduous forest. In that context it is not only important to simulate effects of climatology (temperature, CO 2) on forest evolution, but also to evaluate its NCE. For climatological conditions representative for the mid latitudes the influences of changes in atmospheric temperature and CO 2 levels are simulated. Four compartments are defined in the model, two compartments simulating phytomass functional elements with large temporal biomass fluctuations (green compartment) and phytomass temporal fluctuations that are relatively small (non-green compartment). The litter compartment is also incorporated in the model and its fluxes evaluated. Model runs were executed for two CO 2 scenarios and a climatological record reconstructed for the period covering 1833 till 1989 at a latitude and longitude of 51°N, 2.5°E. It has to be remarked that the addition of 4.5°C to a climatological record for all seasons is a simplification when simulating the effects of a temperature risc. The model outcomc however suggests that the CO 2 mixing ratio rate increase after World War II (WW II) has induced a phytomass increase in young forests. The constraints of the model and its application in Remote Sensing-derivcd data sets is discussed.
Effect of aggregating spatial parameters on modelling forest carbon and water fluxes
Agricultural and forest …, 2006
Estimating spatial variability of carbon and water fluxes is an essential task in ecological modelling. In this article, the sensitivity of carbon and water fluxes to the spatial variability of biochemical and structural properties of canopies is assessed in beech forests using a process-based model (CASTANEA). Firstly, a sensitivity analysis was carried out by varying simultaneously a combination of six key parameters within a realistic range: the above ground wood biomass (B), the soil water reserve (SWR), the canopy clumping factor (CF), the leaf area index (L), the leaf mass per area of sunlit leaves (Msun) and the leaf nitrogen content (N). Secondly, three spatial scales of variability were considered using three study sites whose areas ranged from 0.8 to 1000 ha. The first area studied was a heterogeneous stand located in old-growth forest in Fontainebleau (south of Paris, France). The spatial variability of the biophysical and biochemical ecosystem characteristics in 80 m2 out of 100 m2 was determined. For the two other case studies, we selected a sample of nine plots in which the key input parameters were measured. Sensitivity analysis indicated that photosynthesis and ecosystem respiration show a moderate non-linear response to L, SWR and B. In spite of these non-linear responses, the three case studies revealed that using parameters averaged over the whole area, induces only a slight bias in the estimation of carbon fluxes and almost no bias in the estimation of water fluxes. The implication of the low sensitivity of carbon and water fluxes to parameter aggregation is discussed in relation to the general problem of the scaling up fluxes from ecosystems to large forest regions.