EFFECTS OF FOREST MANAGEMENT AND GRAZING ON BREEDING BIRD COMMUNITIESIN PLANTATIONS OF BROADLEAVED AND CONIFEROUS TREES IN WESTERN ENGLAND

Management options in commercial forestry include choice of conifers o r broadleaves, rotation length, stand size and grazing regime. Each fa ctor potentially affects the conservation value of woodland for birds. Relationships between these factors and the structure and composition of breeding bird communities were examined in 69 stands distributed a cross a range of plantations composed of predominantly native broadlea ved and non-native coniferous trees in the Forest of Dean, western Eng land, in 1992 and 1993. Each stand was classified as one: of three hig h forest types: broadleaved, coniferous or mixed broadleaves and conif ers. Stand size had no effect on bird communities. Species richness an d overall bird abundance increased with forest age when all forest typ es were combined. Within stands of similar ages, there were no consist ent differences in species richness or overall bird abundance between the three forest types or between grazed and ungrazed stands. However, bird communities in mixed stands were intermediate in their overall s pecies composition to those in broadleaved and coniferous stands. Regr ession and gradient analyses (CCA and PCA) revealed that major gradien ts in the species composition of the bird communities were associated with stand age and with tree species composition. The proportion of in dividuals contributed by hole-nesting species was higher in broadleave d than coniferous stands and increased with stand age. The proportion of individuals contributed by migrants was higher in especially the ea rly years, but also in the late years of the rotation. The proportion of migrants was higher in ungrazed than in grazed stands and increased with openness of the canopy and development of low vegetation. The di versity of stands in terms of tree sizes and tree species was positive ly correlated with both number of bird species and overall bird abunda nce. The relevance of these findings is discussed in relation to the i ntegration of bird conservation into coniferous forestry, focusing par ticularly on the value of broadleaved stands and the effects on bird c ommunities of stand structure and grazing pressure. (C) 1998 Elsevier Science Ltd. All rights reserved.