Vegetation maps based on remote sensing are informative predictors of habitat selection of grassland birds across a wetness gradient

Vegetation is a major environmental factor influencing habitat selection in bird species. High resolution mapping of vegetation cover is essential to model the distribution of populations and improve the management of breeding habitats. However, the task is challenging for grassland birds because microhabitat variations relevant at the territory scale cannot be measured continuously over large areas to delineate areas of higher suitability. Remote sensing may help to circumvent this problem. We addressed this issue by using two methods. We (i) mapped the continuous Ellenberg index of moisture and (ii) identified 5 vegetation classes distributed accross the wetness gradient. These two methods produced consistent output maps, but they also provided more information about vegetation structure, and possibly trophic resources. In spite of the apprent uniformity of meadows, our data show that birds do not settle randomly along the moisture and vegetation gradients. Overall birds tend to avoid the driest vegetation classes, i.e. the highest grounds. Thus, vegetation maps based on remote sensing could be valuable tools to study habitat selection and niche partition in grassland bird communities. It is also a valuable tool for conservation and habitat management

Sediment and plant dynamics in saltmarshes pioneer zone: Puccinellia maritima as a key species?

International audienc

Structure de la végétation en prairies humides et réponse à différentes modalités de gestion

National audienceL'étude présentée dans cet article porte sur les prairies permanentes de marais situées dans trois sites principaux: le Marais breton-vendéen, le Marais poitevin et les Marais du Cotentin présentant des systèmes prairiaux sur sol tourbeux. Ces travaux se situent clairement dans le contexte de l'agri-environnement puisque nous cherchons à analyser les effets de différents modes de gestion sur la diversité et la composition de la végétation, dans une analyse dynamique, aussi bien temporelle que spatiale, d'une part ; et la capacité de production fourragère de ces prairies, tant en terme quantitatif que qualitatif d'autre part. Nous cherchons en particulier à comprendre la réponse de ces communautés végétales aux diverses modalités de gestion. Nous nous intéressons : - à l'effet de différentes modalités de pâturage sur la dynamique, la diversité et la production fourragère ; - aux conséquences des différents scénarii de fertilisation ainsi qu'à la variation de dates de fauche ; - et enfin, à l'effet des différentes durées d'inondation sur le niveau de production, sur la diversité ainsi que sur la composition spécifique des prairies de zones inondables

Patrons d'organisation des communautés végétales dans un ancien polder et maintient d'une flore halophytique.

International audienceThe presence of halophytic and sub-halophytic flora in grasslands reclaimed from the sea several centuries ago on the west Atlantic coast in France appears very unusual and the reasons for its survival are still uncertain. our objectives is to document its distribution pattern and to investigate whether its persistence is related to abiotic conditions and/or management practices. Vegetation survey were carried out in seven different sites with 26 relevés on grazed sites and 11 on mown sites. This flora shows some similarity with the vegetation of recent polders and can be classified into groups of species differing by their degree of salt tolerance but also their response to management mode. It was found that halophytes are only present on very saline soils, in a situation where the level of competition with more competitive species is reduced. The sub-halophytes also required low competition on lower soil salinity. In old polders, these two groups only occured on grazed slopes and declined or even disappeared in the absence of grazing. In exclosures, the community became strongly dominated by competitive species and the soil salinity decreased on the slopes. The maintenance of sub-halophytes on old polders seems to be mainly conditioned by competition limitation whereas halophytes showed also a strong dependency to soil salt level, two requirements, which are met on continuously grazed slopes. Grazing maintains inter-specific competition at a low level while trampling increases soil compaction. Soil compaction modifies water and salt circulation, which could explain the high level of soil conductivity observed on grazed slopes

Hétérogénéité spatiale de la végétation induite par les herbivores : conséquences pour la valeur et la production fourragère et la biodiversité en prairies humides

Extrait de documentIn wet natural grasslands, spatial heterogeneity of vegetation appeared related both to abiotic factors and to herbivores' foraging behaviour. An in-situ experimental design showed that the spatial patterns of plant community differ depending of the species of herbivore (horses vs cattle). In term of plant richness, the optimal management is achieved by mixed grazing as horses and cattle show some complementary uses of the resources. The agronomic consequences of the existence of patches have been examined by investigating the biomass production as well as the qualitative value of the vegetation (C/N). The intensity of forage use by herbivore has also been calculated on the field. Some patches contrasted in their agronomic characteristics while others showed similarities despite difference in their floristic composition. The relationships between the forage qualitative and quantitative value and the species composition are discussed. Overall, the agronomic valueof these grasslands appears to have been underestimated and is largely compatible with their biodiversity value. Spatial heterogeneity in grazing and thereafter plant community spatial heterogeneity appears determining for the compatibility between agronomic and biodiversity values

Hétérogénéité spatiale de la végétation induite par les herbivores : conséquences pour la valeur et la production fourragère et la biodiversité en prairies humides

Extrait de documentIn wet natural grasslands, spatial heterogeneity of vegetation appeared related both to abiotic factors and to herbivores' foraging behaviour. An in-situ experimental design showed that the spatial patterns of plant community differ depending of the species of herbivore (horses vs cattle). In term of plant richness, the optimal management is achieved by mixed grazing as horses and cattle show some complementary uses of the resources. The agronomic consequences of the existence of patches have been examined by investigating the biomass production as well as the qualitative value of the vegetation (C/N). The intensity of forage use by herbivore has also been calculated on the field. Some patches contrasted in their agronomic characteristics while others showed similarities despite difference in their floristic composition. The relationships between the forage qualitative and quantitative value and the species composition are discussed. Overall, the agronomic valueof these grasslands appears to have been underestimated and is largely compatible with their biodiversity value. Spatial heterogeneity in grazing and thereafter plant community spatial heterogeneity appears determining for the compatibility between agronomic and biodiversity values

Patrons d'organisation des communautés végétales dans un ancien polder et maintient d'une flore halophytique.

International audienceThe presence of halophytic and sub-halophytic flora in grasslands reclaimed from the sea several centuries ago on the west Atlantic coast in France appears very unusual and the reasons for its survival are still uncertain. our objectives is to document its distribution pattern and to investigate whether its persistence is related to abiotic conditions and/or management practices. Vegetation survey were carried out in seven different sites with 26 relevés on grazed sites and 11 on mown sites. This flora shows some similarity with the vegetation of recent polders and can be classified into groups of species differing by their degree of salt tolerance but also their response to management mode. It was found that halophytes are only present on very saline soils, in a situation where the level of competition with more competitive species is reduced. The sub-halophytes also required low competition on lower soil salinity. In old polders, these two groups only occured on grazed slopes and declined or even disappeared in the absence of grazing. In exclosures, the community became strongly dominated by competitive species and the soil salinity decreased on the slopes. The maintenance of sub-halophytes on old polders seems to be mainly conditioned by competition limitation whereas halophytes showed also a strong dependency to soil salt level, two requirements, which are met on continuously grazed slopes. Grazing maintains inter-specific competition at a low level while trampling increases soil compaction. Soil compaction modifies water and salt circulation, which could explain the high level of soil conductivity observed on grazed slopes

Végétation et gradients écologiques dans les salines abandonnées de l'ouest de la France

International audienceLes marais salés le long de la Côte atlantique française ont été convertis en salines depuis le 7e siècle. La production de sel décline fortement depuis le 18e siècle, menant à l'abandon nombre de ces salines. La forte salinité du sol est une rémanence de la production salicole d'origine et varie d'une saline à l'autre selon la date d'abandon, le régime d'inondation et les conditions de drainage. Les relations entre les communautés de plantes et sept variables environnementales ont été analysées par analyse canonique des correspondances. La durée d'inondation, la conductivité électrique et la sodicité du sol sont le plus fortement corrélées avec les variations dans la végétation. L'Heleocharo-Hippuridetum vulgaris et le Caricetum ripariae occupe les salines au sol peu salé et inondées pendant la plus longue période ; le Scripetum-Maritimi compacti fréquente les salines au sol salé et longtemps submergées ; l'Alopecuro-Juncetum perennis n'est jamais submergé et n'occupe que les sols peu salés. La salinité du sol et la durée de submersion fournissent une explication satisfaisante des variations de la composition spécifique dans les anciennes salines abandonnées mais les pratiques agricoles, spécialement le pâturage, doivent être prises en compte pour comprendre de manière précise leur composition floristique

The response of Puccinellia maritima to burial: A key to understanding its role in salt‐marsh dynamics?

International audienc