The new trends in agricultural policy in Western Europe conduct to new management problems in maintaining and utilizing biological resources. In the South-Western France, the evolution of agricultural practices occurs in two opposite ways. On one hand, the intensification of agriculture leads to simplify the landscape by hedgerows removal, grasslands ploughing and drainage for corn cultivation. On the other hand, the decreasing numbers of cattle and sheep conduct the less fertile parts of the territory to evolve into fallow. These two processes are closely linked on a same territory and important interactions exist between intensive agricultural areas and semi-natural communities. To understand the importance of these interactions and their role in ecological stability of landscapes, we use passerine bird communities as an ecological indicator.
We modelized the relationships between birds and landscape structure from 256 relev6s. Each relev6 includes a bird count point of 20 mn and a description of the landscape feature on the surrounding 6.25 ha. An ordination of the relev6s along the main ecological gradients was realized using Correspondence Analysis. Then, these ordinations where related to the landscape structure with Stepwise and Multiple Regression Analysis. The rate of woody area, the hedgerow network complexity and the rate of fallow land are the main ecological gradients. We have used this model to measure the importance of the changes induced on landscape by a range of management practices differing in intensity. To achieve this aim we compare the displacement of 116 relev6s along the ecological gradients between 1983 and 1988. The changes occurring both in bird composition and landscape structure reveal the ecological impacts of the different management practices (hedgerow removal, drainage, ploughing, decreasing grazing pressure). We examine the behaviour of ecological diversity of landscape units differing in structure and use.