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Les articles de Pierre Mallet
de Pierre Mallet, Arnaud Béchet, Thomas Galewski, François Mesléard, Samuel Hilaire, Gaëtan Lefebvre, Brigitte Poulin, Clelia Sirami
2022, 8
En ligne : www.sciencedirect.com[...]
Increase in pesticide use and landscape homogenization are two key drivers of the decline in farmland biodiversity. The effects of these two drivers are often complex, interactive and vary among taxonomic groups. Our study tested the hypothesis that pesticide use influences the effect of different components of landscape complexity on different taxonomic groups. We sampled 32 rice paddy landscapes of 1 * 1 km in the Camargue (south of France), a wetland internationally recognized as an exceptional biodiversity hotspot. We assessed the abundance and diversity of 7 taxa (plants, bees, butterflies, hoverflies, carabids, spiders and birds) in 3 or 4 crop fields per landscape. For each landscape, we measured the length of different field margins (ditch, grass strip, hedgerow), the proportion of semi-natural areas and crop diversity. For each field, we measured management intensity by the treatment frequency index (TFI) of pesticides. We then tested our hypothesis across 118 fields. Our results show that different components of landscape complexity influence different taxonomic groups: crop diversity and the length of ditches influence bee abundance and species richness, the proportion of semi-natural areas influence spider abundance and species richness, and the length of grass strips influences bird abundance. Moreover, we show that local pesticide use modulates these effects, with more positive effects of landscape complexity in intensively-managed fields. However, we found no interactive effect between landscape complexity and field management for plants, butterflies, hoverflies and carabids. Our study therefore suggests that different components of landscape complexity need to be maintained in order to preserve multiple taxonomic groups. Moreover, it suggests that increasing landscape complexity is particularly relevant to restore biodiversity in intensively-managed fields. Agricultural policies should therefore support the simultaneous increase in semi-natural areas, field margins length and crop diversity to conserve a wide range of taxonomic groups in intensively-managed rice paddy landscapes.Field margins as substitute habitat for the conservation of birds in agricultural wetlands
de Pierre Mallet, Arnaud Béchet, Clelia Sirami, François Mesléard, Thomas Blanchon, Francois Calatayud, Thomas Dagonet, Elie Gaget, Carole Leray, Thomas Galewski
In Peer Community Journal, 3 (August, 2023)
En ligne : peercommunityjournal.org[...]
Breeding birds in agricultural landscapes have declined considerably since the 1950s and the beginning of agricultural intensification in Europe. Given the increasing pressure on agricultural land, it is necessary to identify conservation measures that consume little productive land. We tested the compensation hypothesis which states that field margins may represent substitute habitats for bird species in agricultural wetlands. We monitored bird species in 86 crop fields in rice paddy landscapes of Camargue (southern France), a wetland of international importance for birds. We investigated whether the area of three types of field margins (reed strips, grass strips and hedgerows) within a 500 meter buffer around the centroid of each crop fields had an effect on the abundance of bird species from three groups defined based on their primary habitat (reedbeds, grasslands, and forest edge species). We controlled for the area of each type of semi-natural habitat (wetlands, grasslands, and woodlands), crop diversity (rice, wheat, alfalfa, rape, and market gardening) and mean crop field size. Results show partial support of the compensation hypothesis with species-dependent responses to primary and substitute habitat area. Some species within the reedbed and grassland bird guilds are favored by the area of their primary habitat as well as by the area of field margins, in line with the compensation hypothesis. Eurasian reed warbler is favored by the area of both wetlands and reed strips. Corn bunting is favored by grassland and grass strip areas. We could not confirm the compensation hypothesis for other species. However, this may be due to the fact that most of these species did not respond to their primary habitat. These results therefore suggest that field margins may represent substitute habitats for some species but further studies, in contexts where species are strongly associated with their primary habitat, would be needed to confirm the generality of this hypothesis. Our results also suggest that species response to increasing the area of a field margin type may vary among guilds and even within guilds. Therefore, it may be difficult to favor all species within a given landscape and management actions may need to be tailored to whichever species are locally associated with the highest conservation priority. To tackle this challenge, it may be necessary to design landscape management actions at different spatial scales.
de Lionel Bruhat, Anthony Olivier, Pierre Mallet, Marc Thibault
In Ecologia Balkanica, 18(1) (June, 2026), 219-232
En ligne : eb.bio.uni-plovdiv.bg[...]
Albania's bat fauna is rich but still poorly studied and subject to numerous pressures. One immediate pressure includes the plans to build hydroelectric dams on the Vjosa River and its tributaries, recently classified as a national park. This study was part of an international movement to improve knowledge of both a taxonomic group and a geographical area that have not been studied extensively, to take them into account for conservation purposes. In June 2022, 15 passive bat acoustic sampling sites were set up in four distinct sectors along the Drinos and Suha Rivers, two tributaries of the Vjosa. The Drinos River was included within the national park boundaries in 2023. These recordings were analyzed using automatic identification software and manually verified. Our study identified 16 of the 32 species known to occur in Albania, of which four had fewer than 25 previous records in Albania: Myotis bechsteinii, Myotis emarginatus, Myotis nattereri and Rhinolophus blasii. Our results highlight a high level of activity observed at the sampling sites and the importance of alluvial and riparian hydroecosystems for bats. This study supports the need to take bats into account in the management plans and projects of the Vjosa Wild River National Park. It also produced 135 additional bat records for the country, adding to the 1243 national records.
de Pierre Mallet
Avignon : Université d'Avignon, 2022, 227
L’intensification de l’agriculture est une menace majeure pour la biodiversité. L’homogénéisation des paysages et les changements de pratiques réduisent la quantité et la qualité des habitats disponibles. Dans ce contexte, l’écologie des paysages peut être utilisée dans le but de proposer des modes de gestion agroécologique favorables à la biodiversité.
Dans cette thèse j’ai étudié les effets des interactions entre les bordures de parcelles et les pratiques agricoles ainsi qu’entre les bordures de parcelles et les milieux semi-naturels. J’ai pris pour modèle d’étude les paysages rizicoles du delta du Rhône en Camargue. Les paysages camarguais se caractérisent par de grands espaces de zones humides protégés en réserve, des zones de pâturage extensif et de marais à vocation cynégétique et des parcelles de grande culture. Selon leur localisation, ces cultures sont entourées de milieux semi-naturels ou dans des paysages d’openfields. En tant que zone humide majeure du bassin méditerranéen, il existe dans le delta du Rhône des enjeux de conservation de la biodiversité très importants. La Camargue est donc une zone d’étude intéressante pour travailler sur des modes de gestion agroécologique qui permettent de concilier la production alimentaire et la conservation de la biodiversité.
En étudiant l’effet de l’hétérogénéité du paysage le long d’un gradient d’intensité d’utilisation de produits phytopharmaceutiques, je montre que la présence de milieux semi-naturels surfaciques et de bordures de parcelles a un effet positif plus important pour la biodiversité dans les paysages agricoles intensifs. Ces milieux sont utilisés comme des zones refuges par différentes espèces. J’ai ensuite étudié l’effet des surfaces de bordures de parcelles le long d’un gradient de surface de milieux semi-naturels dans des paysages en agriculture biologique. J’ai ainsi mis en évidence le rôle d’habitat de substitution que peuvent avoir les bordures de parcelles pour les oiseaux nicheurs ainsi que leur utilisation comme habitat complémentaire pour les oiseaux hivernants. Cependant, la diversité des niches des espèces rencontrées dans les milieux agricoles camarguais induit des réponses contrastées aux variations de la quantité des différents types d’infrastructures agroécologiques. Afin de prendre en compte ces variations, j’ai modélisé l’effet de la plantation de haies dans le but d’optimiser la conservation de la biodiversité et la fourniture de services écosystémiques.
En conclusion, l’intensification agricole est une menace majeure pour la biodiversité, mais l’adoption de pratiques agroécologiques peut permettre de réduire ces impacts et même offrir des milieux favorables aux espèces. La prise en compte des milieux agricoles dans les programmes de conservation de la biodiversité en Europe est donc nécessaire.
