Breeding bird communities of second-rotation plantations at different stages of the forest cycle

Capsule Early stages of the plantation forest cycle have distinct bird communities and bird density was significantly higher in the second rotation than in the first for a given age class. Aims To characterize the bird communities in Irish second-rotation plantations and to compare them with those of first-rotation plantations. Methods Point counts were used to survey 20 plantation forests in four age classes (Pre-thicket; Thicket; Mid-rotation; and Mature) in the breeding season of 2007. DISTANCE software was used to generate bird densities. Ordination, indicator species analysis, and GLM were used to analyse the bird communities. Results Bird communities of Pre-thicket and, to a lesser extent, Thicket age classes were distinct from those of more mature forests. Bird communities of Mid-rotation and Mature age classes were indistinguishable from each other and were therefore combined into a single age class (Closed canopy). Pre-thicket held significantly lower total bird density, but significantly higher migrant bird density, than this Closed canopy age class. Bird density was significantly higher in the second rotation in all age classes except for Pre-thicket, but migrant density was significantly higher in Pre-thicket in the second rotation. There was no difference in species richness between the first and second rotation. Conclusions Differences between rotations are probably due to changes in vegetation structure, and the increase in second-rotation forests in Ireland is likely to be a positive development for bird communities. Especially encouraging is the higher migrant bird density in second-rotation Pre-thicket, as some of these species are in decline throughout Europe. However, the largest differences in population density between rotations were exhibited by common species and such species will likely benefit most from future increases in the area of second-rotation plantation forests

The value of plantation forests for plant, invertebrate and bird diversity and the potential for cross-taxon surrogacy

As the area of plantation forest expands worldwide and natural, unmanaged forests decline there is much interest in the potential for planted forests to provide habitat for biodiversity. In regions where little semi-natural woodland remains, the biodiversity supported by forest plantations, typically non-native conifers, may be particularly important. Few studies provide detailed comparisons between the species diversity of native woodlands which are being depleted and non-native plantation forests, which are now expanding, based on data collected from multiple taxa in the same study sites. Here we compare the species diversity and community composition of plants, invertebrates and birds in Sitka spruce- (Picea sitchensis-) dominated and Norway spruce- (Picea abies-) dominated plantations, which have expanded significantly in recent decades in the study area in Ireland, with that of oak- and ash-dominated semi-natural woodlands in the same area. The results show that species richness in spruce plantations can be as high as semi-natural woodlands, but that the two forest types support different assemblages of species. In areas where non-native conifer plantations are the principle forest type, their role in the provision of habitat for biodiversity conservation should not be overlooked. Appropriate management should target the introduction of semi-natural woodland characteristics, and on the extension of existing semi-natural woodlands to maintain and enhance forest species diversity. Our data show that although some relatively easily surveyed groups, such as vascular plants and birds, were congruent with many of the other taxa when looking across all study sites, the similarities in response were not strong enough to warrant use of these taxa as surrogates of the others. In order to capture a wide range of biotic variation, assessments of forest biodiversity should either encompass several taxonomic groups, or rely on the use of indicators of diversity that are not species based