Capacity of older plantations to host bird assemblages of naturally-regenerated conifer forests: A test at stand and landscape levels

Abstract

Conifer plantations are thought to provide lower-quality habitat for many old forest specialists because of their simplified stand structure and relative paucity of habitat elements such as dead wood. However, at the landscape scale, plantations may have a positive influence on biodiversity, e.g. through landscape supplementation. Here, we test the quality of older spruce plantations as breeding habitat for forest birds at local and landscape levels. We compared bird species assemblages of 40–50year-old native spruce plantations with those of mature, naturally-regenerated conifer forests using a Bayesian hierarchical model, which accounts for imperfect detection of species. Median species richness was higher in naturally-regenerated conifer stands than in spruce plantations (29.2 vs. 24.4; 95% probability interval=3.9–5.7), which probably reflects the absence of primary cavity nesters from many stations within plantations. In contrast, more species of canopy nesters were detected in plantations. The proportion of naturally-regenerated conifer forest in the landscape was a predictor of species occurrence for five ground nesters, four primary cavity nesters, and two weak excavators. Older spruce plantations did not provide suitable habitat for some species, mainly cavity nesters. Snag densities in plantations were lower than the estimated threshold requirements for several cavity-nesting birds. Hence, mature, naturally-regenerated forest patches are essential components of intensively-managed forest landscapes to maintain rich forest bird assemblages.