34 research outputs found
Drought and stand susceptibility to attacks by the European spruce bark beetle: A remote sensing approach
Several time-series analyses have demonstrated that after extreme summer droughtbark beetle damage increased. However, studies predicting stand susceptibility overlarge spatial extents are limited by technical constraints in obtaining detailed,spatially-explicit data on infestation spot occurrence.2. Using a unique dataset of georeferenced bark beetle infestation data, we testedwhether the spatial variation of local growing conditions of forest stands, topogra-phy, and landscape variables modified the local occurrence ofIps typographusinfes-tations after a severe hot drought in Central Europe.3. Bark beetle infestation occurrence depended on soil-related aridity intensity, eleva-tion, slope, and soil conditions. We showed that elevation interacted with growingconditions and topography. At low elevations, spruce forests growing on flat areasand wetter soils were more sensitive to the infestations. On the contrary, forestson steep slopes and soils with low water availability were rarely attacked. At thelandscape scale, bark beetle damage increased with host tree cover but decreasedwith compositional diversity.4. Our findings are generally consistent with the growth-differentiation balancehypothesis that predicts that trees growing under chronic dry conditions tend to bemore resistant against biotic disturbances.5. Spruce stands at low elevations located in homogeneous landscapes dominated byspruce were those more exposed to bark beetles in the initial phase of a drought-induced outbrea
StratĂ©gies dâĂ©chantillonnage des dommages forestiers Ă lâĂ©chelle du paysage - Application aux forĂȘts cultivĂ©es de pin maritime (Pinus pinaster, AĂŻt.)
DiplĂŽme : Dr. d'Universit
StratĂ©gies d'Ă©chantillonnage des dommages forestiers Ă l'Ă©chelle du paysage : application aux forĂȘts cultivĂ©es de pin maritime (Pinus pinaster, AĂŻt.)
LâĂ©valuation de la santĂ© des Ă©cosystĂšmes forestiers nĂ©cessite la mise en place de stratĂ©gies de surveillance au sol applicables sur le long terme et selon un continuum dâĂ©chelles spatiales. Entre les rĂ©seaux de placettes permanentes Ă©laborĂ©s de façon empirique Ă l'Ă©chelle europĂ©enne et les protocoles dâobservation Ă portĂ©e trĂšs locale, peu de stratĂ©gies dâĂ©chantillonnage des dommages forestiers ont Ă©tĂ© validĂ©s Ă l'Ă©chelle du paysage (de quelques centaines Ă plusieurs milliers dâhectares), qui est pourtant celle de l'amĂ©nagement forestier. Pour optimiser les performances de lâĂ©chantillonnage des dommages forestiers trois critĂšres ont Ă©tĂ© envisagĂ©s : les caractĂ©ristiques du paysage, la variabilitĂ© des estimations Ă diffĂ©rentes Ă©chelles spatiales et le coĂ»t des observations et des dĂ©placements. Pour cela, deux paysages de forĂȘt cultivĂ©e de pin maritime ont Ă©tĂ© suivi de façon intensive. Lâusage de statistiques non-paramĂ©triques (bootstrap, simulations gĂ©ostatistiques) et des statistiques spatiales a Ă©tĂ© privilĂ©giĂ© pour optimiser la rĂ©partition de lâeffort dâobservation au sein de plans dâĂ©chantillonnage emboĂźtĂ©s. Dans un premier temps, lâoptimisation des rĂ©seaux systĂ©matiques dâobservations actuels (RĂ©seau EuropĂ©en â ICP Forest level I, Inventaire Forestier National) Ă Ă©tĂ© envisagĂ© dans le cadre dâune stratĂ©gie de suivi simultanĂ© de lâensemble des dommages forestiers (biotiques ou abiotiques). Puis, des stratĂ©gies dâĂ©chantillonnage spĂ©cifiques ont Ă©tĂ© envisagĂ©es pour deux insectes ravageurs (la chenille processionnaire du pin Thaumetopoea pityocampa et le scolyte Ips sexdentatus) afin de prendre en compte de façon explicite la distribution spatiale de leurs dommages dans lâĂ©chantillonnage. Les rĂ©sultats montrent quâil est envisageable dâassoir un protocole dâinventaire des dommages forestiers sur les rĂ©seaux dâobservations existant Ă lâĂ©chelle nationale Ă condition de porter la densitĂ© dâĂ©chantillonnage Ă environ 1 placette pour 700 ha. La configuration optimale des placettes rĂ©side alors dans lâobservation de 25 arbres, sĂ©lectionnĂ©s sans discrimination de statut social et intĂ©grant pour partie les arbres en lisiĂšres de peuplement (20%). Seules les populations de T. pityocampa ont montrĂ© une structure spatiale sur plusieurs dizaines de kilomĂštres. Un plan dâĂ©chantillonnage systĂ©matique, dâune maille carrĂ©e comprise entre 2 km et 3km, semble un bon compromis pour lâestimation et la cartographie des densitĂ©s de population de cette chenille dĂ©foliatrice. En revanche, les rĂ©seaux systĂ©matiques dâobservations s'avĂšrent inadaptĂ©s pour lâĂ©valuation de dĂ©gĂąts de trĂšs faible intensitĂ© et/ou agrĂ©gĂ©s dans lâespace comme ceux des scolytes. Ainsi lâĂ©tude rĂ©trospective de dĂ©gĂąts post-tempĂȘte 1999 de I. sexdentatus a montrĂ© l'intĂ©rĂȘt dâune stratĂ©gie dâĂ©chantillonnage par cheminement adaptatif le long des pistes forestiĂšres. Lâutilisation des lisiĂšres forestiĂšres en tant quâ«arbres sentinelles» apparaĂźt prometteuse et ses applications pratiques sont proposĂ©es pour la surveillance sanitaire Ă lâĂ©chelle du paysage.Forest ecosystem health assessment relies on long-term and multiple scales sampling strategies. Neither European networks of permanent plots developed empirically, nor local observation protocols can produce reliable estimates of forest damages over areas ranging from a few hundred to several thousands of hectares. Little attention has been paid to the development of robust sampling designs at the landscape scale, which is however the operational one for forest management. Three criteria were considered to optimize the performance of forest damage sampling: landscape features, variability estimates at different spatial scales and logistics costs of observations. Intensive monitoring was performed on two landscapes of maritime pine plantation forests. Nonparametric statistics (bootstrap, geostatistical simulations) and spatial statistics were used to optimize allocation of sampling effort within nested sampling designs. Firstly, the monitoring of all types of forest damage (biotic or abiotic) was investigated through the optimization of sampling schemes currently applied at the national scale (European Network - ICP forest level I and National Forest Inventory). Then, specific sampling strategies were developed for two insect pests (the defoliator Thaumetopoea pityocampa and the bark beetle Ips sexdentatus), taking into account the spatial distribution of their damage. Increasing the sampling density of national plot networks up to 1/700 ha would be necessary for forest damage survey at the landscape scale. The optimal configuration of inventory plots lies in the observation of about 25 trees, selected without discrimination of social status and partly integrating trees at stand edges (20%). At a large scale, only populations of T. pityocampa showed a spatial structure over several kilometers. A systematic sampling plan, with a square grid between 2 km and 3 km, seems to be a good compromise for estimation and mapping of its nest density. However, systematic plot networks are inadequate for assessing rare and spatially clustered phenomenon such as damage caused by bark beetles damages. A retrospective post-storm 1999 survey of I.sexdentatus damages emphasizes the effectiveness of an adaptive roadside sampling method to monitor this type of damage. The use of forest edges as "sentinel trees" seems promising and its practical applications are proposed for forest health monitoring at the landscape scale
StratĂ©gies d'Ă©chantillonnage des dommages forestiers Ă l'Ă©chelle du paysage : application aux forĂȘts cultivĂ©es de pin maritime (Pinus pinaster, AĂŻt.)
LâĂ©valuation de la santĂ© des Ă©cosystĂšmes forestiers nĂ©cessite la mise en place de stratĂ©gies de surveillance au sol applicables sur le long terme et selon un continuum dâĂ©chelles spatiales. Entre les rĂ©seaux de placettes permanentes Ă©laborĂ©s de façon empirique Ă l'Ă©chelle europĂ©enne et les protocoles dâobservation Ă portĂ©e trĂšs locale, peu de stratĂ©gies dâĂ©chantillonnage des dommages forestiers ont Ă©tĂ© validĂ©s Ă l'Ă©chelle du paysage (de quelques centaines Ă plusieurs milliers dâhectares), qui est pourtant celle de l'amĂ©nagement forestier. Pour optimiser les performances de lâĂ©chantillonnage des dommages forestiers trois critĂšres ont Ă©tĂ© envisagĂ©s : les caractĂ©ristiques du paysage, la variabilitĂ© des estimations Ă diffĂ©rentes Ă©chelles spatiales et le coĂ»t des observations et des dĂ©placements. Pour cela, deux paysages de forĂȘt cultivĂ©e de pin maritime ont Ă©tĂ© suivi de façon intensive. Lâusage de statistiques non-paramĂ©triques (bootstrap, simulations gĂ©ostatistiques) et des statistiques spatiales a Ă©tĂ© privilĂ©giĂ© pour optimiser la rĂ©partition de lâeffort dâobservation au sein de plans dâĂ©chantillonnage emboĂźtĂ©s. Dans un premier temps, lâoptimisation des rĂ©seaux systĂ©matiques dâobservations actuels (RĂ©seau EuropĂ©en â ICP Forest level I, Inventaire Forestier National) Ă Ă©tĂ© envisagĂ© dans le cadre dâune stratĂ©gie de suivi simultanĂ© de lâensemble des dommages forestiers (biotiques ou abiotiques). Puis, des stratĂ©gies dâĂ©chantillonnage spĂ©cifiques ont Ă©tĂ© envisagĂ©es pour deux insectes ravageurs (la chenille processionnaire du pin Thaumetopoea pityocampa et le scolyte Ips sexdentatus) afin de prendre en compte de façon explicite la distribution spatiale de leurs dommages dans lâĂ©chantillonnage. Les rĂ©sultats montrent quâil est envisageable dâassoir un protocole dâinventaire des dommages forestiers sur les rĂ©seaux dâobservations existant Ă lâĂ©chelle nationale Ă condition de porter la densitĂ© dâĂ©chantillonnage Ă environ 1 placette pour 700 ha. La configuration optimale des placettes rĂ©side alors dans lâobservation de 25 arbres, sĂ©lectionnĂ©s sans discrimination de statut social et intĂ©grant pour partie les arbres en lisiĂšres de peuplement (20%). Seules les populations de T. pityocampa ont montrĂ© une structure spatiale sur plusieurs dizaines de kilomĂštres. Un plan dâĂ©chantillonnage systĂ©matique, dâune maille carrĂ©e comprise entre 2 km et 3km, semble un bon compromis pour lâestimation et la cartographie des densitĂ©s de population de cette chenille dĂ©foliatrice. En revanche, les rĂ©seaux systĂ©matiques dâobservations s'avĂšrent inadaptĂ©s pour lâĂ©valuation de dĂ©gĂąts de trĂšs faible intensitĂ© et/ou agrĂ©gĂ©s dans lâespace comme ceux des scolytes. Ainsi lâĂ©tude rĂ©trospective de dĂ©gĂąts post-tempĂȘte 1999 de I. sexdentatus a montrĂ© l'intĂ©rĂȘt dâune stratĂ©gie dâĂ©chantillonnage par cheminement adaptatif le long des pistes forestiĂšres. Lâutilisation des lisiĂšres forestiĂšres en tant quâ«arbres sentinelles» apparaĂźt prometteuse et ses applications pratiques sont proposĂ©es pour la surveillance sanitaire Ă lâĂ©chelle du paysage.Forest ecosystem health assessment relies on long-term and multiple scales sampling strategies. Neither European networks of permanent plots developed empirically, nor local observation protocols can produce reliable estimates of forest damages over areas ranging from a few hundred to several thousands of hectares. Little attention has been paid to the development of robust sampling designs at the landscape scale, which is however the operational one for forest management. Three criteria were considered to optimize the performance of forest damage sampling: landscape features, variability estimates at different spatial scales and logistics costs of observations. Intensive monitoring was performed on two landscapes of maritime pine plantation forests. Nonparametric statistics (bootstrap, geostatistical simulations) and spatial statistics were used to optimize allocation of sampling effort within nested sampling designs. Firstly, the monitoring of all types of forest damage (biotic or abiotic) was investigated through the optimization of sampling schemes currently applied at the national scale (European Network - ICP forest level I and National Forest Inventory). Then, specific sampling strategies were developed for two insect pests (the defoliator Thaumetopoea pityocampa and the bark beetle Ips sexdentatus), taking into account the spatial distribution of their damage. Increasing the sampling density of national plot networks up to 1/700 ha would be necessary for forest damage survey at the landscape scale. The optimal configuration of inventory plots lies in the observation of about 25 trees, selected without discrimination of social status and partly integrating trees at stand edges (20%). At a large scale, only populations of T. pityocampa showed a spatial structure over several kilometers. A systematic sampling plan, with a square grid between 2 km and 3 km, seems to be a good compromise for estimation and mapping of its nest density. However, systematic plot networks are inadequate for assessing rare and spatially clustered phenomenon such as damage caused by bark beetles damages. A retrospective post-storm 1999 survey of I.sexdentatus damages emphasizes the effectiveness of an adaptive roadside sampling method to monitor this type of damage. The use of forest edges as "sentinel trees" seems promising and its practical applications are proposed for forest health monitoring at the landscape scale
Does landscape composition alter the spatiotemporal distribution of the pine processionary moth in a pine plantation forest?
International audienc
Forest foliar phenology disturbances monitoring using satellite based data time series at medium spatial resolution and long-term in-situ observations
International audienceOngoing climate change directly affects tree physiology and forest productivity but is also likely to affect the global vulnerability of forest ecosystems through an amplification of diseases and parasitism. Tree phenology reflects their adaptive responses to climate change and can therefore be used to infer forest condition. Although phenological trends studies based on remotely-sensed data have been widely investigated at the global scale, still little is known on pheno-phases anomalies at regional scales. Sufficient long-term satellite data time series at medium spatial resolution (†1km) are now available to fill this gap but the derived indicators still need to be validated and/or related to disturbance processes. Over the whole French forests and for the last decade, we compared several biophysical parameters from the latest reprocessed products (e.g. MODIS combined and SPOT VEGETATION CYCLOPES data). Chrono-sequences of vegetation indices were computed to investigate the best vegetation health indexes or relative indicators of perturbations: (i) non-parametric modelisation of the forest foliar dynamic was performed using the TIMESAT software to explore inter-annual anomalies (ii) long-term trends and seasonal changes were distinguished by means of the BFAST algorithm. Results were validated and interpreted thanks to 10 years of phenological and sanitary observations provided by the French Permanent Plot Networks for Forest Monitoring (Level I and RENECOFOR). Spatial patterns of tree species phenophases and their anomalies can be depicted. Both latitudinal and altitudinal temperature gradients can be retrieved as well as discrepancies between tree species. Moreover, spatially explicit analysis reveal consistency between satellite-based perturbation index and large scale abiotic (i.e. drought) and biotic (i.e. bark beetles, defoliators) damages inventories. Based on those results, we review the abilities of long-term data series for near real time forest health monitoring and the perspectives of applications in the frame of future satellite missions combining high temporal and spatial resolution
Vine Vigour Characterization using a Multi-temporal X-band SAR Very High Resolution dataset
In the vine-growing industry, the regular acquisition of image data throughout the vine-growing season is of great interest for accurate plot monitoring and grape yield prediction. In this context SAR backscattering data, which can be acquired at any time without being affected by clouds or night-time, seems particularly suitable, especially as their spatial resolution has significantly increased over the past few years. In this paper, we investigate the ability of X-band very high resolution (1 meter) SAR backscattering signal to characterize vine-plots. For that purpose, we used a multi-temporal dataset in order to study three vine-related factors : vine variety, ranks orientation and vine vigour. In our case, we want to monitor a known area for which vine variety and ranks orientation are well defined. As a consequence, we decided to focus on the most useful factor for vine-growers, i.e. vine vigour. The methodology used is a whole sensitivity analysis over a vine vigour classification and regularization process by using only the amplitude of the SAR backscattering
Wavelet based texture modeling for VHR image classification: application to the differentiation of maritime pine forest age classes
National audienc
Epidémiologie du paysage : le cas de la chenille processionnaire du pin (Thaumetopoea pityocampa)
Les perturbations d'origines biotiques qui affectent les forĂȘts sont des phĂ©nomĂšnes qui Ă la fois influencent et sont influencĂ©es par l'hĂ©tĂ©rogĂ©nĂ©itĂ© du paysage. Pourtant, si les relations hĂŽte- ravageur sont couramment apprĂ©hendĂ©es Ă l'Ă©chelle de l'individu ou de la parcelle, relativement peu d'Ă©tudes envisagent la dynamique de la relation entre ce pathosystĂšme et le paysage lui-mĂȘme. C'est dans ce contexte que s'inscrit notre synthĂšse sur la dynamique des populations d'une chenille dĂ©foliatrice des pins en se focalisant sur deux questions particuliĂšres: (i) quels sont les processus qui gouvernent la rĂ©partition de l'insecte dans le paysage ? (ii) peut-on se baser sur la relation paysage/ravageur pour optimiser la surveillance des Ă©cosystĂšmes forestiers ? L'abondance de l'insecte a Ă©tĂ© inventoriĂ©e plusieurs annĂ©es au sein de deux paysages oĂč l'arbre hĂŽte n'est pas un facteur limitant : l'un en condition de plaine au cĆur du massif des Landes de Gascogne et l'autre le long d'un gradient altitudinal au Mont Ventoux. Ces paysages sont dĂ©crits par classification et segmentation morphologique d'images satellites et Ă l'aide de plusieurs mĂ©triques calculĂ©es au sein de zones tampons concentriques de 100 Ă 1000 m autour des points d'inventaires. Les processus Ă l'origine de la rĂ©partition spatiale observĂ©e ont Ă©tĂ© analysĂ©s par la mĂ©thode des vecteurs propres spatiaux. Cette mĂ©thode permet en outre de pouvoir discriminer l'effet de variables paysagĂšres de la composante purement spatiale des relevĂ©s. Les rĂ©sultats tendent Ă confirmer une relation nĂ©gative entre diversitĂ© des espĂšces forestiĂšres et l'herbivorie puisque la proximitĂ© d'arbres non-hĂŽte rĂ©duit significativement l'abondance de l'insecte ravageur. En revanche sa concentration est environ 2,5 fois plus abondante le long des lisiĂšres forestiĂšres. L'analyse Ă diffĂ©rente Ă©chelles spatiales de cette rĂ©ponse Ă la fragmentation permet de bĂątir une stratĂ©gie optimale d'observation des dommages basĂ©e sur l'observation des lisiĂšres forestiĂšres. L'intensitĂ© de l'effet du paysage sur la rĂ©partition spatiale du ravageur sera finalement discutĂ©e en fonction des fluctuations cycliques des niveaux de populations
Satellite-based forest health monitoring using coarse resolution data: Focus on the 2003 and 2011 droughts in France
International audienceNumerous studies showed the impact of droughts events on the seasonal dynamic of satellite-based vegetation index but validation and relation to ground observations is still lacking. Focusing on the impacts of 2003 and 2011 droughts events, we defined and validated forest health indicators using extensive in-situ damage inventories carried out on all French forests. Analysis of vegetation indices dynamics (EVI, LAI) at the national scale was performed using MODIS and SPOT VEGETATION products (MOD13A2 V5 and CYCLOPES V3.1). Satellite-based indicators of (i) crown condition - which is itself a commonly used forest health indicator - and (ii) leaf phenology anomalies were calibrated and validated. In our study, average of CYCLOPES LAI during the growing season is a good proxi of crown condition (r2=0.79, p<0.001). Inter-annual MODIS EVI anomalies can effectively capture drought effects on the vegetation dynamics and its recovery both in time and space