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Durabilité écologique des paysages agricoles et production de bois, bocage et néobocage

Abstract : Typical agricultural landscapes of western Europe and France are called "bocage". They are made of hedgerows delimiting pastures and crop fields, they provide fuel wood especially for farmers. In these landscapes hedgerows and trees have been used for a long time, they produce wood for timber and energy (firewood) and provide many services to farmers. The multifunctionality of these hedgerows has been identified from economic, environmental and social viewpoints. In recent decades, the agricultural intensification and mechanization have led to enlargement of fields and removal of many hedgerows. The changes of farmers' lifestyle have also accelerated this transformation. In this context, we have studied the effects of these changes on the ecological sustainability of bocage , addressing this issue by analysing the sustainability of firewood production. We studied the potentiality of these landscapes for wood production as an index of sustainability of this landscape. Three aspects have been developed: study of the variability of woody biomass in bocage landscapes, evaluation of woody biomass in these landscapes and study of the socio-economic importance of woody biomass in agricultural landscapes.The study area is situated in northern Brittany, France, in the department of Ille-et-Vilaine. We have used a multi-scale approach to estimate the woody biomass from branch to landscape (branch, tree, hedgerow, landscape) and a socio-economic approach to identify the characteristics of farms which use firewood from hedgerows. At the level of branch, an allometric equation has been built to estimate the biomass of branches from their circumference. At the second level (tree), the biomass of branches has been estimated using the equation of the lower level. The variability of the branches biomass has been studied using of tree characteristics and environmental data. At the hedgerow level, the variability of woody biomass has been evaluated according to structure of the hedgerow and environmental factors. At the landscape level, spatial distribution and temporal management of hedgerows has been related to the structure of the landscape and the socioeconomic characteristics of farms. The results confirmed that a multi-scale method is relevant to assess the woody biomass at the landscape level. The circumference of branches is a reliable factor for estimating the biomass of branches. The branch biomass of trees is related to the characteristics of trees. The competition between trees and the land use type of adjacent parcels are important factors in the tree biomass. The structure of the hedgerow and type of tree management (pruning, shredding) are the factors influencing in the hedgerow level. At the landscape level, decreasing of the rate of hedgerow pruning has been observed from 1996 to 2006. During this period, the rate of hedgerow removal has increased. At the landscape level we have observed that hedgerows management and pruning is related to the land use type of adjacent parcels. The socio-economic section has shown the importance of woody biomass as energy source. The planting of hedgerows and their management are related to the economic structure of farms. Integration of grasslands within crop succession is of interest for wood production. We underlined importance of hedgerows in rural economy, mainly for large farms.
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Ali Lotfi. Durabilité écologique des paysages agricoles et production de bois, bocage et néobocage. Ecologie, Environnement. Université Rennes 1, 2008. Français. ⟨tel-00588228⟩

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