Tour du Valat Research Center

Azay-le-Rideau, France

Tour du Valat Research Center

Azay-le-Rideau, France
SEARCH FILTERS
Time filter
Source Type

Davranche A.,University of Angers | Poulin B.,Tour du Valat Research Center | Lefebvre G.,Tour du Valat Research Center
Remote Sensing of Environment | Year: 2013

Reflectance data from multiseasonal SPOT-5 imagery was combined with monthly measures of water levels collected in the RhÔne river delta (Camargue) in 2005 and 2006. Classification tree and regression models using monthly values of 17 multispectral indices and 4 bands, as well as their seasonal variations, were used for predicting the presence and levels of water, independently of vegetation type and density in shallow marshes. Accuracy of the classification model was estimated by cross-validation and by calculating the percentage of correctly classified pixels on the resulting maps using an independent sampling. Goodness-of-fit of the regression model was assessed by calculating the coefficient of correlation between predicted and observed values. Predictive accuracy of both models was estimated by calculating NRMSE for the independent validation sample. Regression model robustness was also tested using Scheffé post-hoc analyses on the residuals. Biophysical parameters of Camargue marsh vegetation were used to interpret misclassifications and model deficiency. Both models were composed of a single variable consisting of a multispectral index using the mid-infrared band. The resulting classification tree provided a cross-validation accuracy of 76% and a map validation accuracy of 83%. With an R. = 0.5, the regression model predicted water level with a 6-cm precision up to 20. cm of water depth. For both approaches, the predictive power of model was most affected by close canopy. This study highlights the usefulness of data mining for long-term monitoring of wetland hydrology based on multispectral indices using the mid-infrared band. © 2013 Elsevier Inc.


Jakob C.,Libelo | Poulin B.,Tour du Valat Research Center
Insect Conservation and Diversity | Year: 2016

Bacillus thuringiensis var. israelensis (Bti) has become the most commonly used larvicide to control mosquitoes worldwide. Bti is considered non-toxic to most organisms, except some Diptera such as chironomids, which are a major prey in wetland food webs. Although Odonata are important predators of mosquitoes and chironomids at the larval and adult stages, no study has ever considered the potential indirect effects of Bti on Odonata abundance through trophic interactions. We addressed this topic in the Camargue where 2500 of the 25 000 ha of mosquito larval biotopes are Bti-sprayed (aqueous solution of VectoBac 12AS at 2.5 L ha-1) whenever mosquito larvae appear in water bodies (i.e. 30-50 aerial treatments overall annually). Adult Odonata were surveyed along a 100-m line transect in spring, summer and autumn at three control and three treated sites over a 5-year period. Mean number of species (9.9 vs. 5.2) and of individuals (100 vs. 50) detected per year were significantly higher in control areas compared to Bti-sprayed areas. Bti treatment contributed to 87.3% of the explained variance in Odonata richness, compared to 2.9% for site, 6.8% for year and 3.0% for salinity effects. These results are coherent with other studies carried out in the same area and time period highlighting a lower abundance of chironomids, and a lower intake of odonates by breeding birds in treated areas. We conclude that mosquito control using Bti should be acknowledged as a potential threat to Odonata. © 2016 The Royal Entomological Society.


Poulin B.,Tour du Valat Research Center | Lefebvre G.,Tour du Valat Research Center | Paz L.,University College London
Journal of Applied Ecology | Year: 2010

The expanding use of selective pest-control agents provides a unique opportunity to study food web interactions in the field while addressing major environmental issues. Bacillus thuringiensis israelensis (Bti) is the most commonly used microbial agent to control mosquitoes worldwide. Using breeding house martins Delichon urbicum as a model species, we assessed the effect of Bti spraying on foraging rates and chick diet prior to and during 3 years of Bti spraying in the Camargue, France. Some 9051 feeding flights and 14 857 prey items were recorded in the early, mid and late nesting season at up to three control and three treated sites. Breeding parameters were assessed during 1 year at two control and two treated sites. Intake of Nematocera (Diptera sub-order including midges and mosquitoes) and their predators (spiders and dragonflies) decreased significantly at treated sites, concurrently with increase of flying ant intake. Small prey (<2·5 mm) were significantly more taken at treated sites, and large prey (>7·5 mm) at control sites, with lower foraging rates at treated sites. Clutch size and fledgling survival were significantly lower at treated sites relative to control with respectively 2·3 vs. 3·2 chicks produced per nest. Breeding success was positively correlated with intake of Nematocera and their predators at the nest level. No previous study has provided compelling evidence of Bti affecting vertebrate populations following the suppression of prey species. Indirect effects caused by repeated application of Bti through food web interactions warrant more attention.6. Synthesis and applications. Bti is considered the most selective and least toxic agent currently available to control mosquitoes. Mosquito-control programmes should integrate non-biased awareness campaigns and mitigation measures balancing the social demands for mosquito reduction with the factors involved in mosquito proliferation and dispersion. Such measures could consist in improved wetland management; reduction in areas and periods of Bti spraying; consideration of alternatives to Bti spraying, such as mosquito traps; specific measures to reinforce animal populations affected by Bti; and suspension of mosquito control in environmentally sensitive areas where nature preservation is a priority. © 2010 The Authors. Journal compilation © 2010 British Ecological Society.


Poulin B.,Tour du Valat Research Center | Duborper E.,Tour du Valat Research Center | Lefebvre G.,Tour du Valat Research Center
Ardeola | Year: 2010

Mist netting with playback was conducted in five marshes in the Camargue (France) in April-May 2009 to document the use of a Mediterranean route by aquatic warblers during spring migration. Six individuals were captured or observed at three sites. Habitat characteristics corresponded to grazed stands dominated by reed Phragmites australis or to stands within reeds dominated by Juncus, Cladium or Schoenoplectus spp., with 7 - 27 cm water levels and a denser vegetation stratum in the first 55 - 80 cm. Mediterranean studies are needed to identify and promote wetland management compatible with the ecology of this globally threatened species.


Poulin B.,Tour du Valat Research Center | Davranche A.,Tour du Valat Research Center | Davranche A.,Friedrich - Alexander - University, Erlangen - Nuremberg | Lefebvre G.,Tour du Valat Research Center
Remote Sensing of Environment | Year: 2010

Ecologists and conservationists need accurate and replicable tools for monitoring wetland conditions in order to develop and implement adaptive management strategies efficiently. The Rhone Delta (Camargue) in southern France encloses 9200 ha of fragmented reed marshes actively managed for reed harvesting, waterfowl hunting or cattle grazing, and holding significant numbers of vulnerable European birds. We used multi-season SPOT-5 data in conjunction with ground survey to assess the predictive power of satellite imagery in modelling indicators of reed structure (height, diameter, density and cover of green/dry stems) relevant to ecosystem management and bird ecology. All indicators could be predicted accurately with a combination of bands (SWIR, NIR) and indices (SAVI, OSAVI, NDWI, DVI, DVW, MSI) issued from scenes of March, June, July, September or December and subtraction between these. All models were robust when validated with an independent set of satellite and field data. The high spatial resolution of SPOT-5 scenes (pixel of 10 × 10 m) permits the monitoring of detailed attributes characterizing the reed ecosystem across a large spatial extent, providing a scientifically-based, replicable tool for managers, stakeholders and decision-makers to follow wetland conditions in the short and long-term. Combined with models on the ecological requirements of vulnerable bird species, these tools can provide maps of potential species ranges at spatial extents that are relevant to ecosystem functioning and bird populations. © 2010 Elsevier Inc. All rights reserved.


Davranche A.,Friedrich - Alexander - University, Erlangen - Nuremberg | Lefebvre G.,Tour du Valat Research Center | Poulin B.,Tour du Valat Research Center
Remote Sensing of Environment | Year: 2010

Multiseason reflectance data from radiometrically and geometrically corrected multispectral SPOT-5 images of 10-m resolution were combined with thorough field campaigns and land cover digitizing using a binary classification tree algorithm to estimate the area of marshes covered with common reeds (Phragmites australis) and submerged macrophytes (Potamogeton pectinatus, P. pusillus, Myriophyllum spicatum, Ruppia maritima, Chara sp.) over an area of 145,000 ha. Accuracy of these models was estimated by cross-validation and by calculating the percentage of correctly classified pixels on the resulting maps. Robustness of this approach was assessed by applying these models to an independent set of images using independent field data for validation. Biophysical parameters of both habitat types were used to interpret the misclassifications. The resulting trees provided a cross-validation accuracy of 98.7% for common reed and 97.4% for submerged macrophytes. Variables discriminating reed marshes from other land covers were the difference in the near-infrared band between March and June, the Optimized Soil Adjusted Vegetation Index of December, and the Normalized Difference Water Index (NDWI) of September. Submerged macrophyte beds were discriminated with the shortwave-infrared band of December, the NDWI of September, the red band of September and the Simple Ratio index of March. Mapping validations provided accuracies of 98.6% (2005) and 98.1% (2006) for common reed, and 86.7% (2005) and 85.9% (2006) for submerged macrophytes. The combination of multispectral and multiseasonal satellite data thus discriminated these wetland vegetation types efficiently. Misclassifications were partly explained by digitizing inaccuracies, and were not related to biophysical parameters for reedbeds. The classification accuracy of submerged macrophytes was influenced by the proportion of plants showing on the water surface, percent cover of submerged species, water turbidity, and salinity. Classification trees applied to time series of SPOT-5 images appear as a powerful and reliable tool for monitoring wetland vegetation experiencing different hydrological regimes even with a small training sample (N = 25) when initially combined with thorough field measurements. © 2009 Elsevier Inc. All rights reserved.


Ernoul L.,Tour du Valat Research Center | Ernoul L.,Aix - Marseille University | Wardell-Johnson A.,University of The Sunshine Coast
Ocean and Coastal Management | Year: 2015

The Integrated Coastal Zone Management (ICZM) protocol for the Mediterranean basin provides a common strategy for coastal management that is applicable to all countries bordering the Mediterranean Sea. Despite the regionalization of ICZM policy, previous studies have shown that ICZM is being implemented differently across the Mediterranean basin. The differences in ICZM implementation could be attributed to the different environmental discourses that are embedded in the perceptions and socio-cultural values in each site. This study analyzed the differences in environmental discourses as they apply to ICZM policy in two Mediterranean Deltas (Rhone Delta in southern France and Gediz Delta in Western Turkey). A cross-section of 39 (Rhone Delta) and 54 (Gediz Delta) participants contributed to a survey questionnaire. Qualitative and quantitative techniques provided insights into complex relationships between environmental ideals, ideologies and practice in the adoption of ICZM principles. The results demonstrated incorporation of ICZM in environmental discourse in both sites with distinct differences in ICZM strategies. Differences in environmental discourses have implications for applying the ICZM protocol. The identification of these differences provides a more effective focus for conservation strategies accounting for specific context. © 2014 Elsevier Ltd.


Ernoul L.,Tour du Valat Research Center | Ernoul L.,Aix - Marseille University | Wardell-Johnson A.,University of The Sunshine Coast
Environmental Conservation | Year: 2013

The Integrated Coastal Zone Management protocol of the Barcelona Convention sets governance objectives for countries bordering the Mediterranean Sea. This protocol emphasizes collaborative approaches to acknowledge the role of local people in coastal management. Evaluating the quality of governance processes is critical if coastal zone values are to be effectively managed in times of global climate change. This study examined the structure and attributes of collaborative governance networks in two Mediterranean deltas, the Camargue (France) and Gediz Delta (Turkey). A deliberative social catchment sampling was used to target actors with physical, cultural, social or economic ties. Forty-five different organizations/professions were interviewed using a standardized questionnaire to identify the frequency and quality of contacts, information flows, and subject matter relevant to natural resource management. There were higher levels of degree centrality and reciprocal ties in the Camargue, while the Gediz Delta had a greater homogeneity of actors, with one centralized influential actor. Civil society played a greater role in the Camargue network, and government organizations were more central in the Gediz Delta. The differences between the two sites call into question the use of the same integrated management strategies and suggest the need to acknowledge the importance of existing governance models and relationships within local contexts. © Foundation for Environmental Conservation 2013.


Following its high selectivity and low toxicity to nontarget organisms, Bacillus thuringiensis var. israelensis (Bti) has become the most commonly used microbial agent to control mosquitoes worldwide. Considered non-toxic to mammals, birds, fish, plants and most aquatic organisms, Bti direct effects on the nontarget fauna are largely limited to non-biting midges (Chironomidae). Studies addressing the indirect effects of Bti through food web perturbations are scanty and showed no significant results. Mosquito-control in southern France was implemented in 1965 using various insecticides over 400 km of coast. In spite of a high mosquito nuisance, the Camargue wetlands were excluded from this control programme to preserve biodiversity. The expanding use of Bti has prompted the implementation of an experimental mosquito control in 2006 involving 2500 of the 25,000 ha of larval biotopes of the Camargue, accompanied by impact studies on the nontarget fauna. Using birds from natural and human-inhabited areas as model species, we assessed trophic perturbations caused by three years of Bti applications. The preliminary results of this 5-yr programme revealed significant effects of Bti spraying on abundance of reed-dwelling invertebrates serving as food to passerines, as well as on the diet and breeding success of house martins nesting in rural estates and small towns. Very few studies (if any) have provided such compelling evidence of an insecticide affecting vertebrate populations, putting into question the environmental-friendly character of Bti, at least in some areas. The significance of these results are discussed within a wider context and completed with an analysis of the current Bti bibliography to highlight and orient priorities for future research on this topic. © 2011 Elsevier Masson SAS.


Lefebvre G.,Tour du Valat Research Center | Germain C.,Tour du Valat Research Center | Poulin B.,Tour du Valat Research Center
Environmental Modelling and Software | Year: 2015

Mediterranean wetlands are increasingly managed to maintain their functions and services following modification in water allocation, embankment and climate change, calling for proactive and adaptive water management. In a first step, we used long-term monitoring of water levels in 37 adjacent embanked marshes in the Camargue as a repeated non-controlled experiment to build a hydrological model. Without information on water input/output by marsh users, we could nevertheless estimate evapotranspiration under flooding and dry conditions, and soil water coefficient. The model provided a high predictive accuracy (adjusted R2 = 0.73-0.83) of monthly water levels when applied to an independent sample of 12 marshes. In a second step we developed an interactive decision-aid tool that allows users to visualize the impact of their management strategy (desired water level at a specific month) on subsequent water levels, and their consequence on different components of the ecosystem over a 10-yr period. © 2015 Elsevier Ltd.

Loading Tour du Valat Research Center collaborators
Loading Tour du Valat Research Center collaborators