The Effects on Song-Bird Populations of Upland Afforestation with Spruce

Abstract

Large coniferous plantations have been established widely in uplands previously used for rearing sheep and cattle, causing fundamental changes in the wild life of these areas. Breeding song-birds were censused in south-west Scotland on upland moorland grazed by sheep and in spruce plantations at different stages of growth. The commonest song-bird species were meadow pipit and skylark on unplanted areas, meadow pipit in establishment plantation, willow warbler and wren in thicket, and goldcrest, chaffinch and wren in polestage and thinned plantations. Total song-bird densities were 40–70 pairs km ⁻² on unplanted heather, 70–130 pairs km ⁻² on unplanted grass, 125–200 pairs km ⁻² on 6 year old trees, 230–290 pairs km ⁻² on 12–14 year old trees, and 300–440 pairs km ⁻² on trees over 20 years old. Bird species diversity was also greatest in trees over 20 years old, with one exception. Many bird species depend on unafforested moorland, but were not censused since they are too sparsely distributed. Their loss is to be set against the gain in numbers of smaller song birds following afforestation which was inferred from the study plots. From the standpoint of bird conservation, diverse forest structure and the retention of some large unafforested upland areas is advocated.