RIPARIAN EDGE EFFECTS ON BOREL BALSAM FIR BIRD COMMUNITIES

Riparian forests are often identified as prime habitat for wildlife be cause of the presence of particular plant communities and edges creati ng a highly developed and diversified vegetation structure. However, i n the northeastern boreal forests of Canada, where narrow land-water e cotones with abrupt edges are quite common, the relative habitat value of riparian forests remains to be demonstrated. We compared bird comm unities of eight pairs of riparian and nonriparian plots, similar in v egetation structure and composition, to Verify the relative value for breeding birds of typical coniferous riparian forest stands of the sou thern boreal region of eastern Quebec. Bird abundance (P = 0.02), rich ness (P = 0.03), and diversity (P = 0.02) were significantly higher in the riparian stands, where the spatial sequence of three distinct hab itats (a balsam fir (Abies balsamea (L.) Mill.) - northern white cedar (Thuja occidentalis L.) forest, a narrow alder (Alnus rugosa (Du Roi) Spreng.) - grass wetland, and water) created high horizontal vegetati on diversity. In riparian stands median bird richness and density were , respectively, 23.5 species and 437.5 territories/km(2) compared with 19.0 species and 348.2 territories/km(2) for interior stands. Nine sp ecies were observed exclusively in riparian plots. In addition to the species usually found in the studied nonriparian forests, the riparian plots were used by species typically related to the water edge such a s the Northern Waterthrush (Seiurus noveboracensis Gmelin) and Rusty B lackbird (Euphagus carolinus Muller) as well as species associated wit h the shrub and grass wetland such as the American Robin (Turdus migra torius L.), the Veery (Catharus fuscescens Stephens), and the Common Y ellowthroat (Geothlypis trichas L.). The shrub-foraging guild showed h igher abundance in riparian stands. The tree-foraging and tree-bole fo raging guilds, however, were comparable in both groups of stands. In t his study, the natural conditions prevailing along he riparian sites a ppeared mostly positive for the breeding-bird community; it created wh at is perceived as being an ''edge effect.'' The edge effect can be de fined, in this case, as being the additional density and number of spe cies induced by the added horizontal vegetation diversity created by t he close association of three extremely different ecosystems: a forest stand, an aquatic ecosystem, and a narrow but distinct shrub-grass we tland. This also confirms the necessity of distinguishing natural edge s that are permanent features of the landscape from induced edges crea ted by human activity.