Relationships between bird assemblages, vegetation structure, and floristic composition of mosaic patches in riparian forests

Abstract

The vegetation structure and the plant taxonomic composition of riparian forests, together with the birds, were mapped and analysed. The forest 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 plant taxonomic composition associated with plant succession showed the strongest correlations with the variables of bird community. Disturbances caused by forestry is correlated with reduced bird species richness in forest patches of all ages. Canonical correspondence analyses of the bird data constrained by the vegetation data allowed us to identify that variables that explain most of the variance in bird data are those related strongly to succession. Partial CCA revealed the relative influence of plant structure versus floristic variables as well as their combined influence on bird community structure (17, 17, 21 % respectively). When the same analysis is applied after removal of early-successional vegetation types, the importance of floristic variables increased.