Josephine Pithon

Effects of growth stage and tree species composition on breeding bird assemblages of plantation forests

Capsule Bird species assemblages are strongly dependent on growth stage and forest structure, but do not appear to be greatly affected by tree species composition. Aims To investigate changes in bird species composition of plantation forests in relation to crop tree species and forest growth stage. Methods We surveyed populations of birds in 44 plantation forests throughout Ireland in the summers of 2001 and 2002. Our study sites represented three combinations of tree species (pure Sitka Spruce Picea sitchensis, pure Ash Fraxinus exelsior, and Sitka Spruce/Ash mixed at inter-stand level) at five ages (4–8 years, 9–17 years, 23–29 years, 35–50 years and 50+ years). We used ordinations and indicator species analyses to explain the influence of growth stage and tree species composition on the bird assemblages of these forests. Results Bird species assemblage is dependent on growth stage. Changes in bird species composition over the commercial forest cycle are related to shrub layer and proximity to the forest edge. The bird assemblages of pre-canopy closure forests are typical of open habitats, some of the constituent bird species being of conservation concern within Ireland. As forests mature, these are replaced by commoner, more generalist species. We found no significant effect of tree species on bird species assemblage. Possible reasons for this include the relatively narrow range of tree species mixtures studied, and the paucity of forest specialist birds in Ireland. Conclusions Forest management for bird diversity in Ireland should promote the shrub layer in and around forest plantations, and ensure that new afforestation does not take place in areas with diverse communities of open-habitat birds. Opportunities for Irish forest plantations to provide habitat for bird forest specialists may be limited.

Selection of nesting habitat by Montagu's Harriers Circus pygargus and Hen Harriers Circus cyaneus in managed heaths

Capsule Montagus Harriers avoided tree plantations and selected plots with dense heath of intermediate height, while sympatric Hen Harriers preferred afforested or taller plots of heath. Aims To investigate relationships between vegetation structure and nest selection by Montagus and Hen Harriers. Methods We defined three vegetation strata: upper, intermediate and lower. Height and cover of plant species in each stratum were recorded in a 9-m2 area centred on nests or unused random points. Statistical analysis was performed to reveal predictors for classifying plots (i) with a Montagus Harrier nest, (ii) with a Hen Harrier nest and (iii) without a nest. Results Montagus Harriers selected places where tree cover was less than 25%, the maximum height of the upper stratum was 1.87 m, and the cover of the intermediate stratum was greater than 75%. Hen Harriers nested either in plots where the upper stratum was higher than 1.87 m, or where tree coverage was greater than 25%. Conclusions To encourage the breeding of Montagus Harriers, the planting of pine should be avoided and the heath should be rejuvenated before it reaches 1.80 m in height. For Hen Harriers, certain plots of heath higher than 2 m should be kept. In agricultural landscapes, patches of managed shrubland or heathland could help conservation of both species.