Diverse temperate forest bird assemblages demonstrate closer correspondence to plant species composition than vegetation structure

The aggregate structure of vegetation has long provided a strong conceptual basis for understanding the ecological separation of faunal species, while correspondence with plant species composition remains largely underdeveloped and considered secondary to structure. Longstanding ecological debate on the matter has likely been sustained by statistical methods incapable of accommodating an entire species composition in the explanatory role. We used direct ordination methodologies (predictive co-correspondence and canonical correspondence analyses) that allow the comparison of prediction levels between composition and structure for understanding avian assemblage composition in a temperate forestland in southeastern Ohio. Compositional (birds and woody plants) and structural (both vertical and horizontal dimensions) data were collected from point samples comprising a spectrum in topography and successional state. Total woody plant composition (11.22%) explained more (cross-validatory) variation in avian species composition than structure, quantified with dense LiDAR recordings (7.35%) and field methods (6.31%). Plant composition assumed an integrative character, synthesizing aspects of environmental condition, structure, and most likely species-specific preferences for tree and shrub species that structural indices alone could not for predicting avian species composition. These results conflict with the traditional view that structure be most influential to avian assemblage composition. Instead these results demonstrate that plant and avian assemblages are closely linked, and that plant species per se can be a powerful tool for predicting avian habitat. More importantly, in furthering ecological understanding, it is critical to consider the complex web of interacting processes that make up temperate forest ecosystems, in which composition occupies a key position.