RELATIONSHIPS BETWEEN BIRD ASSEMBLAGES, VEGETATION STRUCTURE, AND FLORISTIC COMPOSITION OF MOSAIC PATCHES IN RIPARIAN FORESTS

The vegetation structure and the plant taxonomic composition of ripari an forests, together with the birds, were mapped and analysed. The for est plots were 100 m wide and 1 600 to 2 000 m long, and were located near lake Grand Lieu, Brittany, France. The plots were not homogeneous , but a mosaic of different vegetation types. The patches of the same vegetation type were combined. We recognized 21 vegetation types, but we retained only 16 that were of sufficient size to neutralize species -area effects. Variables of vegetation structure as well as variables of plane taxonomic composition associated with plant succession showed the strongest correlations with the variables of bird community. Dist urbances caused by forestry is correlated with reduced bird species ri chness in forest patches of all ages. Canonical correspondence analyse s of the bird data constrained by the vegetation data allowed us to id entify that variables that explain most of the variance in bird data a re those related strongly to succession. Partial CCA revealed the rela tive influence of plant structure versus floristic variables as well a s their combined influence on bird community structure (17, 17, 21% re spectively). When the same analysis is applied after removal of early- successional vegetation types, the importance of floristic variables i ncreased.