Avian species richness in relation to forest management practices in early seral tree plantations

Background/Question/Methods

Managers of landscapes dedicated to commodity production require information about how current practices influence biological diversity.  Individual species or communities may be threatened by forestry practices that truncate or simplify seral stages required to fulfill life history requirements.  The degradation and loss of early seral breeding habitat has been associated with declines in Neotropical migrant bird populations in the Pacific Northwest, USA.  These declines may be exacerbated by current practices that reduce hardwood and broadleaf shrub cover, features that comprise high quality breeding habitat for numerous species, in order to promote rapid stand regeneration.We used a hierarchical model to evaluate the relationships between avian species richness and habitat covariates that represent stand management intensity on 212 forest stands in the Coast Range, Oregon, USA, and analyzed the model using a Bayesian approach.The model estimated species-specific occurrence and the effects of elevation and percent cover of conifer, broadleaf, deciduous broadleaf, and hardwood plant species, while accounting for imperfect detection of species. 

 Results/Conclusions

We used the fitted model to make predictions of species richness within forest stands that varied in elevation and habitat structure.  Total species richness and leaf-gleaner (a subset of the community which is expected to respond negatively to control of hardwood and deciduous broadleaf vegetation) richness responded positively to increases in both conifer and hardwood cover.  When imperfect detection was ignored, we did not find relationships between species or leaf-gleaner richness and any of the covariates.  Our results revealed that individual and community responses, even for leaf-gleaning species that were expected to be strongly dependent on deciduous vegetation, were positively associated with conifer and hardwood cover.  To promote the development and maintenance of high quality breeding habitat, stand management strategies should retain or increase hardwood vegetation while achieving desired stocking levels of conifer vegetation.  In landscapes where intensive management predominates, the maintenance of a varied vegetation community may be crucial for maintaining breeding bird populations.