Effects of vegetation structure on the diversity of breeding bird communities in forest stands of non-native black pine (Pinus nigra A.) and black locust (Robinia pseudoacacia L.) in the Czech Republic

- Bird communities were surveyed in stands of non-native and native trees.
- Bird species richness increased with increasing vegetation heterogeneity.
- Non-native tree stands were impoverished in habitat specialists and canopy foragers.
- The gradient broadleaved-coniferous stands determined bird community composition.
- Tree origin is of less importance for birds compared to basic stand characteristics.

Forest management affects stands' vegetation structure, which influences bird communities. Since the effects of forest practices are usually more pronounced if the exotic tree species are planted, we surveyed bird communities and mapped the vegetation structure in stands of non-native broad-leaved and coniferous trees, black locust and black pine, in a central European country, the Czech Republic. By means of spatial analysis - generalized least squares models - we investigated whether the positive relationship between bird species richness in various ecological groups and vegetation heterogeneity is weakened by an assumed negative effect of the exotic tree origin. Further, we tested whether the bird community composition is more impacted by tree origin (native and non-native) than forest type (coniferous and broad-leaved) using multivariate direct gradient redundancy analyses. We found that total bird species richness, species richness of habitat specialists, ground foragers and foliage gleaners significantly increased with increasing vegetation heterogeneity after taking tree origin into account. Since there was higher vegetation heterogeneity in non-native tree stands, we suggest that the potential benefits of this higher heterogeneity were suppressed by some other (unmeasured) characteristics (e.g. limited food supply) of these stands, which might also be the reason for lower richness of habitat specialists and canopy foragers. The most important gradient in the bird community composition was from broad-leaved to coniferous stands irrespective of tree origin. The effect of tree origin was expressed as the secondary gradient, albeit still significant. It seems that the birds' adaptations to different leaf morphology play more important role in structuring bird communities than the influence of tree origin. Our results indicate that the forest management should focus on the increase of the vegetation heterogeneity in native tree stands to maximize total bird species richness, and on avoiding establishment of non-native tree plantations to prevent loss of habitat specialist birds.