45 research outputs found
Extraction de fragments forestiers et caractérisation de leurs évolutions spatio-temporelles pour évaluer l'effet de l'histoire sur la biodiversité : une approche multi-sources
Biodiversity in landscapes depends on landscape spatial patterns but can also be influenced by landscape history. Indeed, some species are likely to respond in the longer term to habitat disturbances. Therefore, in recent years, landscape dynamics have become a possible factor to explain current biodiversity. The aim of this thesis in GIS is part of this historical ecology context. We are dealing with automatic extraction of forest patches and characterization of their spatiotemporal evolution. The objective is to evaluate forest dynamics effects on current diversity of forest hoverflies. (Diptera: Syrphidae) in the agri-forestry landscape of Coteaux de Gascogne. The proposed general approach consists of three main steps: (1) the forest spatial database production from heterogeneous sources, (2) forest patches matching and characterization of their spatiotemporal evolution, (3) species-habitat modeling while integrating history as one of the factors likely to explain hoverflies diversity. Several methodological contributions were made. We proposed a new geometric correction approach based on kernel ridge regression to make consistent past and present selected data sources. We also developed an automatic extraction approach of forest from Historical Map of France of the 19th century. Finally, spatial uncertainty effects on ecological models responses have been assessed. From an ecological viewpoint, a significant effect from historical continuity of patches on forest hoverflies diversity was revealed. The most isolated fragments presented an extinction debt or a colonization credit according to area dynamics occurred in the last time-period (1970-2010). As it turns out, 30 years was not sufficient for forest hoverflies to reach new equilibrium after isolated habitat changes.La biodiversitĂ© dans les paysages dĂ©pend des caractĂ©ristiques de ce paysage mais peut aussi ĂȘtre influencĂ©e par son histoire. En effet, certaines espĂšces ne rĂ©agissent pas immĂ©diatement Ă une perturbation mais peuvent montrer un temps de rĂ©ponse plus ou moins long. De ce fait, la prise en compte de l'Ă©volution de l'habitat des espĂšces est devenue un enjeu important en Ă©cologie depuis quelques annĂ©es, pour mieux comprendre la prĂ©sence ou la diversitĂ© biologique actuelle. L'objectif de cette thĂšse en gĂ©omatique s'inscrit dans ce contexte applicatif d'Ă©cologie historique. Le sujet que nous traitons porte sur l'extraction automatique d'Ăźlots boisĂ©s et la caractĂ©risation de leur Ă©volution spatio-temporelle depuis le milieu du XIXe siĂšcle pour modĂ©liser l'effet de leur trajectoire historique sur la diversitĂ© actuelle en syrphes forestiers (Diptera : Syrphidae). Le site d'Ă©tude est un paysage agri-forestier des Coteaux de Gascogne. La dĂ©marche gĂ©nĂ©rale proposĂ©e se compose de trois Ă©tapes principales : (1) la constitution de la base de donnĂ©es spatiales des Ăźlots boisĂ©s intĂ©grant plusieurs sources de donnĂ©es hĂ©tĂ©rogĂšnes, (2) l'appariement des Ăźlots boisĂ©s aux diffĂ©rentes dates avec la caractĂ©risation de leur Ă©volution spatio-temporelle, (3) la modĂ©lisation statistique des relations espĂšces-habitats intĂ©grant l'histoire comme un des facteurs explicatifs de la diversitĂ© en syrphes observĂ©e. Plusieurs contributions mĂ©thodologiques ont Ă©tĂ© apportĂ©es Ă cette dĂ©marche. Nous avons proposĂ© une nouvelle mĂ©thode de correction gĂ©omĂ©trique fondĂ©e sur la rĂ©gression ridge Ă noyau pour rendre compatible les donnĂ©es spatiales anciennes et actuelles mobilisĂ©es. Nous avons Ă©galement dĂ©veloppĂ© une approche et un outil de vectorisation automatique des forĂȘts dans les dessins-minutes de la carte d'Etat-Major du XIXe siĂšcle. Enfin, une premiĂšre Ă©valuation de l'impact de l'incertitude spatiale sur la rĂ©ponse des modĂšles espĂšces-habitats a Ă©galement Ă©tĂ© initiĂ©e. D'un point de vue Ă©cologique, les rĂ©sultats ont rĂ©vĂ©lĂ© un effet significatif de la continuitĂ© temporelle des habitats sur la diversitĂ© en syrphes forestiers. Nous avons montrĂ© que les forĂȘts les plus isolĂ©es prĂ©sentaient une dette d'extinction ou un crĂ©dit de colonisation selon le type d'Ă©volutions apparues au cours de la derniĂšre pĂ©riode Ă©tudiĂ©e (1979-2010). Il s'est avĂ©rĂ© qu'une durĂ©e de 30 ans n'Ă©tait pas suffisante aux syrphes forestiers pour qu'ils retrouvent un Ă©tĂ© d'Ă©quilibre Ă la suite d'une Ă©volution spatiale de leur habitat isolĂ©
Spatial uncertainty effects on a species-landscape relationship model in ecology
In this study, we explore the effects of geometrical uncertainty in an existing species-landscape relationship model in the hoverfly communities. We also investigate how geometrical uncertainties affect a more complex model including both current forest patch features and past forest features. Because of a possible time-lag in biological responses to forest changes such as fragmentation, the historical dimension is added to the first model. The proposed approach relies on three spatial sources enabling to get forest fragments at different times: historical map (~1850), aerial black and white photographs (1954) and orthorectified photographs (2010). Firstly, we analyze the effect of the spatial data production method (manual versus automatic) on models using current forest patches only. Then, we build a more complex model including past changes in forest size. As previously, the effect of production-based uncertainty was assessed by comparing the models based on forests extracted manually and automatically. We address finally the impact of positional accuracy on the historical map by using a Monte Carlo simulation approach. Global results show that responses of the statistical models are strongly affected by spatial uncertainty in inputs
Utilisation des sĂ©ries temporelles dâimages Sentinel-2 pour la cartographie de lâoccupation du sol dans un contexte de modĂ©lisation de la biodiversitĂ©
La connaissance de lâoccupation du sol actualisĂ©e est une donnĂ©e essentielle pour de nombreuses applications
scientifiques et opĂ©rationnelles. Ă ce titre, il sâagit dâune donnĂ©e permettant de dĂ©river plusieurs variables
essentielles de biodiversitĂ©, telles que lâĂ©tendue et la fragmentation des Ă©cosystĂšmes ainsi que la structure
paysagĂšre, variables fortement reliĂ©es au potentiel de biodiversitĂ© dâun paysage (Skidmore et al., 2015). Elle
reprĂ©sente une donnĂ©e dâentrĂ©e essentielle des modĂšles prĂ©dictifs ou de simulation paysagĂšre dĂ©veloppĂ©es en
recherche en Ă©cologie du paysage. Ă lâheure actuelle, il existe plusieurs jeux de donnĂ©es dâoccupation du sol de
rĂ©fĂ©rence, comme Corine Land Cover (CLC) Ă lâĂ©chelle europĂ©enne ou la BD TOPOÂź de lâIGN Ă lâĂ©chelle
nationale française. Ces deux jeux de donnĂ©es permettent de dĂ©crire lâoccupation du sol de maniĂšre exhaustive
et harmonisée sur de larges étendues géographiques. Cependant, la faiblesse de CLC réside dans sa fraßcheur
temporelle, Ă savoir que sa diffusion intervient tardivement par rapport Ă la pĂ©riode temporelle quâelle dĂ©crit. Si
CLC dispose dâune typologie trĂšs dĂ©taillĂ©e, intĂ©grant des notions dâusage du sol, la BD TOPOÂź, si elle dĂ©crit
prĂ©cisĂ©ment les Ă©lĂ©ments permanents du paysage, nâidentifie pas diffĂ©rentes classes annuelles du paysage
telles que les cultures. LâavĂšnement rĂ©cent de la mission spatiale Sentinelle-2 qui fournit de sĂ©ries temporelles
dâimages satellites, Ă forte capacitĂ© de revisite (5 jours) et une rĂ©solution spatiale dĂ©camĂ©trique sur lâensemble
de la surface terrestre, ouvre ainsi de nouvelles opportunitĂ©s dans la cartographie de lâoccupation du sol
actualisĂ©e Ă grande Ă©chelle. Dans ce sens, le CESBIO avec des contributions de lâUMR Dynafor, dans le cadre
du centre dâexpertise scientifique « Occupation du Sol » (CES OSO) du PĂŽle ThĂ©matique Surfaces
Continentales THEIA a dĂ©veloppĂ© une chaĂźne opĂ©rationnelle de classification supervisĂ©e automatique dâimages
Sentinelle-2 et Landsat-8 (iota2) produisant une cartographie de lâoccupation du sol actualisĂ©e. Lâoccupation du
sol est dĂ©crite grĂące Ă 17 classes, couvrant les grands ensembles paysagers (urbain, agricole et semi-naturel), Ă
une résolution spatiale de 10 m et une unité minimale de collecte de 0.01 ha (UMC). La précision globale proche
de 90% permet son utilisation tant dans des contextes opĂ©rationnels et scientifique dâaide Ă la dĂ©cision (Inglada
et al., 2017). Cette présentation décrira, dans une premiÚre partie, les caractéristiques de ce produit
cartographique, de sa méthode de production et de sa qualité statistique. Dans une seconde partie, la question
de lâincertitude spatiale de cette carte dâoccupation du sol sera abordĂ©e. Une comparaison avec un jeu de
donnĂ©es dâoccupation du sol digitalisĂ© manuellement sera prĂ©sentĂ©e au travers dâune modĂ©lisation spatialisĂ©e
espĂšce-habitat fondĂ©e sur la surface, lâhĂ©tĂ©rogĂ©nĂ©itĂ© et la connectivitĂ© forestiĂšre dâun paysage agricole pour
expliquer la richesse spĂ©cifique de syrphes (ordre des mouches) (Herrault et al., 2016). Les rĂ©sultats tendent Ă
montrer un effet nĂ©gligeable de lâincertitude spatiale sur les performances du modĂšle alors quâen parallĂšle le
recours Ă la cartographie par tĂ©lĂ©dĂ©tection de lâoccupation du sol permet dâenvisager une analyse plus
systĂ©matique de lâeffet de la matrice paysagĂšre dans son ensemble sur la biodiversitĂ©
The influence of spatial and temporal discontinuities of forest habitats on the current presence of flightless saproxylic beetles
Flightless saproxylic beetles were selected in order to study the impact of temporal and spatial discontinuity of forests. They were chosen because: (1) they are unable to fly, making them dispersal-limited species, (2) they have a saproxylic diet, which means they are closely linked to the forest, and (3), they have rarely been studied. Forest temporal continuity was expected to be the main factor explaining the presence of these species, modulated by the
past and present amount of forest in the surrounding landscape. Twenty-seven forests, distributed into three zones, were sampled in southwestern France. Flightless saproxylic beetles were surveyed using a Winkler extractor and a Berlese funnel. Their presence/absence were modelled using generalised linear mixed models, with zone variable as random effect. Two species showed significant zone effect and were only or more present in the zone with
the highest present forest amount in a 0.5 km radius. In the model that converged, the only selected variable was the past amount of forest in the landscape. The size of the forest, the presence of dead wood and the forest temporal continuity were not included in this model. The importance of the amount of forest in the landscape supports the hypothesis that dispersal-limited species are affected by landscape characteristics. This study demonstrates an important link between the presence of Dienerella clathrata and the amount of forest in
the past, which led to an indicator species analysis being performed
Forest fragments extraction and characterization of their spatiotemporal evolution to evaluate the effects of history on biodiversity : a multi-source approach
La biodiversitĂ© dans les paysages dĂ©pend des caractĂ©ristiques de ce paysage mais peut aussi ĂȘtre influencĂ©e par son histoire. En effet, certaines espĂšces ne rĂ©agissent pas immĂ©diatement Ă une perturbation mais peuvent montrer un temps de rĂ©ponse plus ou moins long. De ce fait, la prise en compte de l'Ă©volution de l'habitat des espĂšces est devenue un enjeu important en Ă©cologie depuis quelques annĂ©es, pour mieux comprendre la prĂ©sence ou la diversitĂ© biologique actuelle. L'objectif de cette thĂšse en gĂ©omatique s'inscrit dans ce contexte applicatif d'Ă©cologie historique. Le sujet que nous traitons porte sur l'extraction automatique d'Ăźlots boisĂ©s et la caractĂ©risation de leur Ă©volution spatio-temporelle depuis le milieu du XIXe siĂšcle pour modĂ©liser l'effet de leur trajectoire historique sur la diversitĂ© actuelle en syrphes forestiers (Diptera : Syrphidae). Le site d'Ă©tude est un paysage agri-forestier des Coteaux de Gascogne. La dĂ©marche gĂ©nĂ©rale proposĂ©e se compose de trois Ă©tapes principales : (1) la constitution de la base de donnĂ©es spatiales des Ăźlots boisĂ©s intĂ©grant plusieurs sources de donnĂ©es hĂ©tĂ©rogĂšnes, (2) l'appariement des Ăźlots boisĂ©s aux diffĂ©rentes dates avec la caractĂ©risation de leur Ă©volution spatio-temporelle, (3) la modĂ©lisation statistique des relations espĂšces-habitats intĂ©grant l'histoire comme un des facteurs explicatifs de la diversitĂ© en syrphes observĂ©e. Plusieurs contributions mĂ©thodologiques ont Ă©tĂ© apportĂ©es Ă cette dĂ©marche. Nous avons proposĂ© une nouvelle mĂ©thode de correction gĂ©omĂ©trique fondĂ©e sur la rĂ©gression ridge Ă noyau pour rendre compatible les donnĂ©es spatiales anciennes et actuelles mobilisĂ©es. Nous avons Ă©galement dĂ©veloppĂ© une approche et un outil de vectorisation automatique des forĂȘts dans les dessins-minutes de la carte d'Etat-Major du XIXe siĂšcle. Enfin, une premiĂšre Ă©valuation de l'impact de l'incertitude spatiale sur la rĂ©ponse des modĂšles espĂšces-habitats a Ă©galement Ă©tĂ© initiĂ©e. D'un point de vue Ă©cologique, les rĂ©sultats ont rĂ©vĂ©lĂ© un effet significatif de la continuitĂ© temporelle des habitats sur la diversitĂ© en syrphes forestiers. Nous avons montrĂ© que les forĂȘts les plus isolĂ©es prĂ©sentaient une dette d'extinction ou un crĂ©dit de colonisation selon le type d'Ă©volutions apparues au cours de la derniĂšre pĂ©riode Ă©tudiĂ©e (1979-2010). Il s'est avĂ©rĂ© qu'une durĂ©e de 30 ans n'Ă©tait pas suffisante aux syrphes forestiers pour qu'ils retrouvent un Ă©tĂ© d'Ă©quilibre Ă la suite d'une Ă©volution spatiale de leur habitat isolĂ©.Biodiversity in landscapes depends on landscape spatial patterns but can also be influenced by landscape history. Indeed, some species are likely to respond in the longer term to habitat disturbances. Therefore, in recent years, landscape dynamics have become a possible factor to explain current biodiversity. The aim of this thesis in GIS is part of this historical ecology context. We are dealing with automatic extraction of forest patches and characterization of their spatiotemporal evolution. The objective is to evaluate forest dynamics effects on current diversity of forest hoverflies. (Diptera: Syrphidae) in the agri-forestry landscape of Coteaux de Gascogne. The proposed general approach consists of three main steps: (1) the forest spatial database production from heterogeneous sources, (2) forest patches matching and characterization of their spatiotemporal evolution, (3) species-habitat modeling while integrating history as one of the factors likely to explain hoverflies diversity. Several methodological contributions were made. We proposed a new geometric correction approach based on kernel ridge regression to make consistent past and present selected data sources. We also developed an automatic extraction approach of forest from Historical Map of France of the 19th century. Finally, spatial uncertainty effects on ecological models responses have been assessed. From an ecological viewpoint, a significant effect from historical continuity of patches on forest hoverflies diversity was revealed. The most isolated fragments presented an extinction debt or a colonization credit according to area dynamics occurred in the last time-period (1970-2010). As it turns out, 30 years was not sufficient for forest hoverflies to reach new equilibrium after isolated habitat changes
Using the new French Land Cover Map (OSO) as spatial inputs in forest ecological modeling
International audienceSince 2016, a new French Land Cover Map (the OSO product) is available at a country scale with 17 land cover classes representing main land cover types (urban, agricultural and semi-natural). It is based on a fully automatic processing chain using Sentinel-2 image time series and Landsat images. The classification accuracy is around 90\% and reasonably enables to use this map as spatial inputs in species-habitat model. However, information on potential spatial uncertainty effects in these ecological models remain limited yet.In this study, we explore the impact of spatial uncertainty on a Generalized Linear Model (GLM) that investigates area and connectivity effects of 48 woodlands on the species richness of forest specialist hoverflies. We compared three different models calibrated from the three OSO products available (10m raster, 20m raster and the 20m vectorized product).Firstly, AREA and CONNECTIVITY were derived for all detected sampled forest fragments in each forest product. Then, a statistical protocol was defined in order to evaluate performances and sensitivity of each model : (1) a Leave One Out Cross Validation (LOOCV) was applied. Then, we computed mean and standard deviation for indicators usually analyzed in ecological statistical models outputs : the deviance explained (D2), the significance of regression coefficients (p-value) and the predictive capability (Root Mean Squared Error - RMSE) ; (2) We used a boostrapping technique (1000 runs) to approximate the distribution and test the stability of regression coefficients estimates for each model. Therefore, for each k-1 cross validation run, we also analyzed the standard deviation of the RMSE.Preliminar results show that spatial inputs derived from OSO products had no impacts on the predictive capability of the models (Rho = 0.85, p < 0.001). Nevertheless, we observed strong impacts on the quantity of Deviance explained (Mean Absolute Error (D2) = -0.12 ± 0.08) and the significance of the coefficients. AREA effect on the response variable remains significant with the « raster 10 m » (p-value <0.05) product but disappears in the other modelâs configurations. The significance level of the connectivity variable also decreases with the increase of spatial resolution and/or simplification. It became strictly non-existent in the model based 192 on variables from the « vectorized product"
Quality assessment of MODIS vegetation continuous fields of tree cover over France
International audienceThe MODIS VCF is the unique product that enable to map tree cover at globalscale and assess its dynamic for almost two decades. It is used for a wide rangeof environmental studies and provide essential knowledge on the distribution oftrees on earth. The product has already been validated in different areas ofthe world. However, information on its accuracy remains very patchy and theunderstanding of the spatial distribution of errors limited.In this study, we investigate the accuracy of the MODIS VCF percent treecover layer (collection 5, 250-m spatial resolution) over France using the mostdetailed topographical vector database available at the national scale (BDTopo,French mapping agency IGN; minimum mapping unit of 500 m2). We alsocompare the VCF data with a new national land cover map (the OSO product)based on a fully automatic processing 191 chain using Sentinel-2 image time series.In a first time, we estimate for each VCF pixel (n = 5,909,620), the corresponding tree cover percentage of the two reference datasets, while ensuring consistency between the production years. Then, a set of multiple independentvariables are computed including some environmental factors (such as elevationand slope), the level of fragmentation of woody vegetation, and the land covercomposition in the VCF pixel. Finally, uncertainty is quantified from classicalstatistical indicators (Root-Mean-Squared Error, Mean Bias Error, Mean Abso-lute Error) and differences in tree cover are mapped, to understand the spatialpattern and possible sources of errors.Preliminary results show significant differences between the VCF tree coverand the reference products despite the high positive correlation (Spearmanâsrho correlation = 0.75 for VCF vs BDTopo, and rho = 0.74 for VCF vs OSO;p<0.001). Negative bias with high variability was measured relative to BDTopo(MBE = -12.04 ± 22.41%; RMSE = 25.44%) and OSO (MBE = -6.59 ± 22.34%;RMSE=23.29%). Understimation of VCF tree cover is mainly observed from25% to 75% of cover. Overestimation also appears, mainly in pixels dominatedby grasslands. These findings corroborate previous studies, except for sparselytree areas. No relationship is observed with the quality level of the VCF product.Differences are only slightly explained by slope and elevation.This study contributes to the effort of independant validation of the VCFproduct and may help to better understand the classification errors in variouslandscape contexts
Assessing the Influence of Landscape on Biodiversity Using the QGIS Plugin LecoS
International audienceThis chapter illustrates the implementation of a conventional methodology in landscape ecology. The method is based on an existing landscape representation, i.e. a land cover description of the landscape which consists of the following steps: computation of a set of features and use of the features as explanatory variables in a descriptive model built on the observed biodiversity. The chapter shows the feasibility of the analysis in landscape ecology by combining several free tools interfaced with GIS software: the remote sensing tool, Orfeo Toolbox; the landscape descriptors calculation tool, Landscape ecology statistics (LecoS); and the statistical modeling tool, R, and its development interface, R Studio. The proposed threeâstep method is adapted to the free and openâaccess software, Quantum GIS (QGIS 2.18 Windows), so that a user, without large expertise in remote sensing and geomatics, can use it without signing up for use of software licenses
Vectorisation automatique des forĂȘts dans les minutes de la carte d'Etat-Major du 19 e siĂšcle
International audienceDans cet article, nous proposons une nouvelle mĂ©thode pour extraire automatiquement les forĂȘts dans les cartes d'Etat-major du 19 Ăšme siĂšcle numĂ©risĂ©es. La dĂ©marche proposĂ©e est constituĂ©e de quatre Ă©tapes principales : filtrage de l'image, changement d'espace colorimĂ©trique, identification des forĂȘts Ă l'aide d'un dĂ©tecteur non paramĂ©trique (SVDD), post-traitement. La mĂ©thode est suffisamment robuste pour prendre en compte la diversitĂ© des reprĂ©sentations possibles des forĂȘts dans ces cartes anciennes. Les rĂ©sultats montrent des performances Ă©levĂ©es avec une prĂ©cision globale de dĂ©tection obtenue de 95%. Cette approche ouvre de nouvelles perspectives pour les diffĂ©rentes Ă©tudes environnementales incluant une dimension historique
Reconstructing forest changes in a fragmented landscape of southwest France from multiple data sources: ecological implications
International audienc