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Modelling forest management within a global vegetation model - Part 2: Model validation from a tree to a continental scale / V. Bellassen in Ecological modelling, vol 222 n° 1 (janvier 10, 2011)  

Public [article]  inEcological modelling > vol 222 n° 1 (janvier 10, 2011) . - pp 57 - 75 Titre : Modelling forest management within a global vegetation model - Part 2: Model validation from a tree to a continental scale Type de document : Article/Communication Auteurs : V. Bellassen, Auteur ; G. Le Maire, Auteur ; O. Guin, Auteur ; Jean-François Dhôte, Auteur ; Philippe Ciais, Auteur ; Nicolas Viovy, Auteur Année de publication : 2011 Article en page(s) : pp 57 - 75 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Termes IGN] biomasse forestière [Termes IGN] carbone [Termes IGN] modélisation de la forêt [Termes IGN] stress hydrique Mots-clés libres : ORCHIDEE-FM Résumé : (auteur) The construction of a new forest management module (FMM) within the ORCHIDEE global vegetation model (GVM) allows a realistic simulation of biomass changes during the life cycle of a forest, which makes many biomass datasets suitable as validation data for the coupled ORCHIDEE-FM GVM. This study uses three datasets to validate ORCHIDEE-FM at different temporal and spatial scales: permanent monitoring plots, yield tables, and the French national inventory data. The last dataset has sufficient geospatial coverage to allow a novel type of validation: inventory plots can be used to produce continuous maps that can be compared to continuous simulations for regional trends in standing volumes and volume increments. ORCHIDEE-FM performs better than simple statistical models for stand-level variables, which include tree density, basal area, standing volume, average circumference and height, when management intensity and initial conditions are known: model efficiency is improved by an average of 0.11, and its average bias does not exceed 25%. The performance of the model is less satisfying for tree-level variables, including extreme circumferences, tree circumference distribution and competition indices, or when management and initial conditions are unknown. At the regional level, when climate forcing is accurate for precipitation, ORCHIDEE-FM is able to reproduce most productivity patterns in France, such as the local lows of needleleaves in the Parisian basin and of broadleaves in south-central France. The simulation of water stress effects on biomass in the Mediterranean region, however, remains problematic, as does the simulation of the wood increment for coniferous trees. These pitfalls pertain to the general ORCHIDEE model rather than to the FMM. Overall, with an average bias seldom exceeding 40%, the performance of ORCHIDEE-FM is deemed reliable to use it as a new modelling tool in the study of the effects of interactions between forest management and climate on biomass stocks of forests across a range of scales from plot to country. Numéro de notice : A2011-285 Affiliation des auteurs : non IGN Thématique : FORET Nature : Article DOI : 10.1016/j.ecolmodel.2010.08.038 Date de publication en ligne : 22/10/2010 En ligne : https://doi.org/10.1016/j.ecolmodel.2010.08.038 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=102459 [article]

Voir aussi

• Modelling forest management within a global vegetation model - Part 1: Model structure and general behaviour / V. Bellassen in Ecological modelling, vol 221 n° 20 (octobre 2010)  

Modelling forest management within a global vegetation model - Part 1: Model structure and general behaviour / V. Bellassen in Ecological modelling, vol 221 n° 20 (octobre 2010)  

Public [article]  inEcological modelling > vol 221 n° 20 (octobre 2010) . - pp 2458 - 2474 Titre : Modelling forest management within a global vegetation model - Part 1: Model structure and general behaviour Type de document : Article/Communication Auteurs : V. Bellassen, Auteur ; G. Le Maire, Auteur ; Jean-François Dhôte, Auteur ; Philippe Ciais, Auteur ; Nicolas Viovy, Auteur Année de publication : 2010 Article en page(s) : pp 2458 - 2474 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Termes IGN] biomasse forestière [Termes IGN] carbone [Termes IGN] feuillu [Termes IGN] modèle de simulation [Termes IGN] modélisation de la forêt [Termes IGN] production primaire nette Mots-clés libres : ORCHIDEE Résumé : (auteur) This article describes a new forest management module (FMM) that explicitly simulates forest stand growth and management within a process-based global vegetation model (GVM) called ORCHIDEE. The net primary productivity simulated by ORCHIDEE is used as an input to the FMM. The FMM then calculates stand and management characteristics such as stand density, tree size distribution, tree growth, the timing and intensity of thinnings and clear-cuts, wood extraction and litter generated after thinning. Some of these variables are then fed back to ORCHIDEE. These computations are made possible with a distribution-based modelling of individual tree size. The model derives natural mortality from the relative density index (rdi), a competition index based on tree size and stand density. Based on the common forestry management principle of avoiding natural mortality, a set of rules is defined to calculate the recurrent intensity and frequency of forestry operations during the stand lifetime. The new-coupled model is called ORCHIDEE-FM (forest management). The general behaviour of ORCHIDEE-FM is analysed for a broadleaf forest in north-eastern France. Flux simulation throughout a forest rotation compare well with the literature values, both in absolute values and dynamics. Results from ORCHIDEE-FM highlight the impact of forest management on ecosystem C-cycling, both in terms of carbon fluxes and stocks. In particular, the average net ecosystem productivity (NEP) of 225 gC m−2 year−1 is close to the biome average of 311 gC m−2 year−1. The NEP of the “unmanaged” case is 40% lower, leading us to conclude that management explains 40% of the cumulated carbon sink over 150 years. A sensitivity analysis reveals 4 major avenues for improvement: a better determination of initial conditions, an improved allocation scheme to explain age-related decline in productivity, and an increased specificity of both the self-thinning curve and the biomass-diameter allometry. Numéro de notice : A2010-686 Affiliation des auteurs : non IGN Thématique : FORET Nature : Article DOI : 10.1016/j.ecolmodel.2010.07.008 Date de publication en ligne : 20/08/2010 En ligne : https://doi.org/10.1016/j.ecolmodel.2010.07.008 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=102452 [article]

Voir aussi

• Modelling forest management within a global vegetation model - Part 2: Model validation from a tree to a continental scale / V. Bellassen in Ecological modelling, vol 222 n° 1 (janvier 10, 2011)  

Toward universal broad leaf chlorophyll indices using PROSPECT simulated database and hyperspectral reflectance measurements / G. Le Maire in Remote sensing of environment, vol 89 n° 1 (15/01/2004)  

Public [article]  inRemote sensing of environment > vol 89 n° 1 (15/01/2004) . - pp 1 - 28 Titre : Toward universal broad leaf chlorophyll indices using PROSPECT simulated database and hyperspectral reflectance measurements Type de document : Article/Communication Auteurs : G. Le Maire, Auteur ; C. François, Auteur ; Eric Dufrêne, Auteur Année de publication : 2004 Article en page(s) : pp 1 - 28 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de télédétection [Termes IGN] albedo [Termes IGN] chlorophylle [Termes IGN] erreur moyenne quadratique [Termes IGN] feuillu [Termes IGN] indice de végétation [Termes IGN] réflectance végétale [Termes IGN] réseau neuronal artificiel Résumé : (Auteur) Fifty-three leaves were randomly sampled on different deciduous tree species, representing a wide range of chlorophyll contents, tree ages, and leaf structural features. Their reflectance was measured between 400 and 800 nm with a 1-nm step, and their chlorophyll content determined by extraction. A larger simulated database (11,583 spectra) was built using the PROSPECT model, in order to test, calibrate, and obtain universal indices, i.e., indices applicable to a wide range of species and leaf structure. To our knowledge, almost all leaf chlorophyll indices published in the literature since 1973 have been tested on both databases. Fourteen canonical types of indices (published ones and new ones) were identified, and their wavelengths calibrated on the simulated database as well as on the experimental database to determine the best wavelengths and, hence, the best performances in chlorophyll estimation for each index types. These indices go from simple reflectance ratios to more sophisticated indices using reflectance first derivatives (using the Savitzky and Golay method). We also tested other nondestructive methods to obtain total chlorophyll concentration: SPAD (Minolta Camera, Osaka, Japan) and neural networks. The validity of the actual PROSPECT model is challenged by our results: Important discordances are found when the indices are calculated with PROSPECT compared to experimental data, especially for some indices and wavelengths. The discordance is even greater when the indices are determined with PROSPECT and applied on the experimental database. A new calibration of PROSPECT is therefore necessary for any study aiming at using simulated spectra to determine or to calibrate indices. The "peak jump" and the multiplepeak feature observed on the first derivative of the reflectances (e.g., in the Red-Edge Inflection Point [REIP] index) has been investigated. It was shown that chlorophyll absorption alone can explain this feature. The peak jump disqualifies the REIP to be a valuable chlorophyll index. A simple modified difference ratio gave the best results among all published indices (cross-validated RMSE 2.1 [ug/cm2 on the experimental database). After calibration on the experimental database, modified Simple Ratio (mSR) and modified Nonnalized Difference (mND) indices gave the best performances (RMSECV = 1. 8 ug/cm2 on the experimental database). The new Double Difference (DD) index, although not the best on the experimental database (RMSECV = 2.9 [ug/cm2), has the best results on the larger simulated database (RMSE = 3.7 gg/cm2 ) and is expected to give good results on larger experimental databases. The best reflectance-based indices give better performances than the current commercial nondestructive device SPAD (RMSECV = 4.5 ug/cm2). In this leaf-level study, the best indices are very near from each other, so that complex methods are useless: REIP-like, neural networks, and derivative-based indices are not necessary and give worst results than simpler properly chosen indices. These conclusions will certainly be different for a canopy-level study, where the derivative-based indices may perform significantly better than the other ones. Numéro de notice : A2004-008 Affiliation des auteurs : non IGN Thématique : FORET/IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.rse.2003.09.004 En ligne : https://doi.org/10.1016/j.rse.2003.09.004 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=26536 [article]