Agricultural land-use change and ash (Fraxinus excelsior L.) colonization in Pyrenean landscapes: an interdisciplinary case study

 ONLINE FIRSTInternational audienceChanges in agricultural land use are responsible for significant modifications in mountain landscapes. This study is part of an interdisciplinary research on the processes and consequences of spontaneous afforestation of Pyrenean landscapes by ash, and the possibilities for its management. We address the relationships between vegetation dynamics and land-use change from the combination of an agricultural study of change in farm management and an ecological study of grassland colonization by ash. In the framework of a village case study, we characterized parcels management and land-use histories, and analyzed the dynamics of the composition of grassland vegetation communities. From a joint analysis of the results obtained in each discipline, we discuss the limitations and comple-mentarities of the two approaches for the interdisciplinary assessment of the afforestation process

Detecting clear-cuts and decreases in forest vitality using MODIS NDVI time series

This paper examines the potential of MODIS-NDVI time series for detecting clear-cuts in a coniferous forest stand in the south of France. The proposed approach forms part of a survey monitoring the status of forest health and evaluating the forest decline phenomena observed over the last few decades. One of the prerequisites for this survey was that a rapid and easily reproducible method had to be developed that differentiates between forest clear-cuts and changes in forest health induced by environmental factors such as summer droughts. The proposed approach is based on analysis of the breakpoints detected within NDVI time series, using the “Break for Additive Seasonal and Trend” (BFAST) algorithm. To overcome difficulties detecting small areas on the study site, we chose a probabilistic approach based on the use of a conditional inference tree. For model calibration, clear-cut reference data were produced at MODIS resolution (250 m). According to the magnitude of the detected breakpoints, probability classes for the presence of clear-cuts were defined, from greater than 90% to less than 3% probability of a clear-cut. One of the advantages of the probabilistic model is that it allows end users to choose an acceptable level of uncertainty depending on the application. In addition, the use of BFAST allows events to be dated, thus making it possible to perform a retrospective analysis of decreases in forest vitality in the study area

Modelling and simulating change in reforesting mountain landscapes using a social-ecological framework

Natural reforestation of European mountain landscapes raises major environmental and societal issues. With local stakeholders in the Pyrenees National Park area (France), we studied agricultural landscape colonisation by ash (Fraxinus excelsior) to enlighten its impacts on biodiversity and other landscape functions of importance for the valley socio-economics. The study comprised an integrated assessment of land-use and land-cover change (LUCC) since the 1950s, and a scenario analysis of alternative future policy. We combined knowledge and methods from landscape ecology, land change and agricultural sciences, and a set of coordinated field studies to capture interactions and feedback in the local landscape/land-use system. Our results elicited the hierarchically-nested relationships between social and ecological processes. Agricultural change played a preeminent role in the spatial and temporal patterns of LUCC. Landscape colonisation by ash at the parcel level of organisation was merely controlled by grassland management, and in fact depended on the farmer's land management at the whole-farm level. LUCC patterns at the landscape level depended to a great extent on interactions between farm household behaviours and the spatial arrangement of landholdings within the landscape mosaic. Our results stressed the need to represent the local SES function at a fine scale to adequately capture scenarios of change in landscape functions. These findings orientated our modelling choices in the building an agent-based model for LUCC simulation (SMASH - Spatialized Multi-Agent System of landscape colonization by ASH). We discuss our method and results with reference to topical issues in interdisciplinary research into the sustainability of multifunctional landscapes

Biodiversity indicators in organic and conventional farming systems: main results from the European project BIOBIO

In the framework of the European project BIOBIO, we compared between countries habitat and cumulated species richnesses of plants, wild bees, spiders and earthworms, measured in 169 conventional and organic farms belonging to 10 case studies in 10 European countries. For the French case study (Gascony Valleys and Hills), correlations between direct (habitat and taxonomic richnesses) and indirect (agricultural practices) indicators of biodiversity within 8 conventional and 8 organic farms, were calculated. Results showed that the main driver of biodiversity at the farm level was the number of cultivated and above all semi-natural habitats, inthe French case study region as well as inthe other regions. This factor partially explained the highest biodiversity level of the French case study region. However, farming practices, specific or not to the organic and conventional systems, most often drove biodiversity parameters at the habitat level. In fine, the project proposed the BIOBIO method for monitoring biodiversity in farms

Indicateurs de biodiversité dans les exploitations agricoles biologiques et conventionnelles des Vallées et Coteaux de Gascogne, cas d’étude français du projet européen BIOBIO

Dans le cadre du projet européen BIOBIO, nous avons comparé entre pays les richesses en habitats et richesses spécifiques cumulées de quatre groupes taxonomiques (plantes, abeilles sauvages, araignées, vers de terre), de 169 exploitations biologiques ou conventionnelles appartenant à 10 pays. Pour le cas d’étude français, Vallées et Coteaux de Gascogne, les corrélations entre indicateurs directs (richesses spécifiques des taxons et habitats) et indirects (pratiques agricoles) de biodiversité, relevés dans 8 exploitations conventionnelles et 8 biologiques, ont été recherchées. Les résultats montrent que le nombre d’habitats cultivés et surtout semi-naturels par exploitation est le principal facteur déterminant le niveau de biodiversité à cette échelle, pour le cas d’étude français comme pour les autres cas d’étude. Ce facteur explique en partie le plus haut niveau de biodiversité observé pour le cas d’étude français. Néanmoins, les pratiques, spécifiques ou non des modes de production biologique et conventionnelle, gouvernent généralement les paramètres de biodiversité à l’échelle de l’habitat. In fine, le projet propose la méthode BIOBIO de suivi de la biodiversité dans les exploitations agricoles

Patterns of ash (Fraxinus excelsior L.) colonization in mountain grasslands: the importance of management practices

International audienceWoody colonization of grasslands is often associated with changes in abiotic or biotic conditions or a combination of both. Widely used as fodder and litter in the past traditional agro-pastoral system, ash (Fraxinus excelsior L.) has now become a colonizing species of mountain grasslands in the French Pyrenees. Its present distribution is dependent on past human activities and it is locally controlled by propagule pressure and abiotic conditions. However, even when all favourable conditions are met, all the potentially colonizable grasslands are not invaded. We hypothesize that management practices should play a crucial role in the control of ash colonization. From empirical field surveys we have compared the botanical composition of a set of grasslands (present and former) differing in management practices and level of ash colonization. We have displayed a kind of successional gradient positively linked to both ash cover and height but not to the age of trees. We have tested the relationships between ash presence in grassland and management types i.e. cutting and/or grazing, management intensity and some grassland communities' features i.e. total and local specific richness and species heterogeneity. Mixed use (cutting and grazing) is negatively linked to ash presence in grassland whereas grazing alone positively. Mixed use and high grazing intensity are directly preventing ash seedlings establishment, when low grazing intensity is allowing ash seedlings establishment indirectly through herbaceous vegetation neglected by livestock. Our results show the existence of a limit between grasslands with and without established ashes corresponding to a threshold in the intensity of use. Under this threshold, when ash is established, the colonization process seems to become irreversible. Ash possesses the ability of compensatory growth and therefore under a high grazing intensity develops a subterranean vegetative reproduction. However the question remains at which stage of seedling development and grazing intensity these strategies could occur

Conception de zone de filtration des eaux effluentes de parcelles agricoles : approche bibliographique

It seems that scientific knowledge is good enough to plan the creation or maintenance of buffer ground covers able to purify surface waters by eliminating part of its pollutants, among which nitrates. The understanding of purification ecological treatments permits to define the main efficiency conditions of buffer areas. They must be set up at the scale of hydrographic units, by acting as upstream as possible. The purification conditions are not contradictory with a development of the buffer areas, even an intensive one. Wood production or grazing are often possible. It is the duty of the authorities to design these areas not as production tools, but as services to the community, and to take measures necessary to their development. On another hand, some data seem to indicate that the buffer areas are less costly to society than other measures with similar efficiency. / Il apparaît que les connaissances scientifiques sont suffisantes pour envisager la création ou l'entretien de formations végétales tampons capables d'épurer les eaux de la nappe superficielle d'une partie de ses polluants, dont les nitrates. La connaissance des processus écologiques d'épuration permet de cerner les principales conditions d'efficacité des zones tampons. Leurs mise en oeuvre doit se concevoir à l'échelle d'une unité hydrographique, en intervenant le plus en amont possible. Les conditions d'épuration ne sont pas contradictoires avec une exploitation des zones tampons, même intensive. La production des bois ou le pâturage sont souvent possibles. Il revient aux pouvoirs publics de concevoir ces zones non pas comme des outils de production, mais comme des services pour la collectivité, et de prendre les mesures nécessaires à leur développement. Par ailleurs, quelques données semblent montrer que les zones tampons sont moins coûteuses à la société que d'autres mesures d'efficacité comparables