Abstract
ABSTRACTCapsule: Smaller woodlands not only support fewer species but also show different avian community composition due to loss of woodland interior and an increase in edge habitat.Aims: To use observed community composition changes, rather than traditional total species richness-area relationships, to make area-specific management recommendations for optimizing woodland habitat for avian communities in fragmented landscapes.Methods: 17 woodlands were selected in Oxfordshire, UK, with areas between 0.2 and 120 ha. Three dawn area searches were conducted in each woodland between 1st April and 28th May 2016 to record encounter rates for each species. The impact of internal habitat variation on woodland comparability was assessed using habitat surveys.Results: Woodlands with area less than 3.6 ha showed a significant positive relationship between total avian species richness and woodland area. Woodlands with area over 3.6 ha were all consistent with a mean (± se) total richness of 25.4 ± 0.6 species, however the number of woodland specialists continued to increase with woodland area. Woodland generalists dominated the total encounter rate across the area range, however the fractional contribution of woodland specialists showed a significant positive correlation with woodland area, while the fractional contribution of non-woodland species significantly decreased. Non-woodland species numbers peaked in mid-sized woodlands with enhanced habitat heterogeneity.Conclusions: Community composition analysis enabled more targeted recommendations than total species richness analysis, specifically: large woodlands (over 25 ha) in southern UK should focus conservation efforts on providing the specific internal habitats required by woodland specialists; medium-sized woodlands (between approximately 4 and 25 ha) should focus on promoting internal habitat variety, which can benefit both woodland species and non-woodland species of conservation concern in the surrounding landscape; small woodlands (under 4 ha) should focus on providing nesting opportunities for non-woodland species and on improving connectivity to maximize habitat for woodland generalists and facilitate movement of woodland specialists.
Highlights
Deforestation has reduced woodland cover in the UK to just 11% (Smith & Gilbert 2003) and much of this woodland consists of relatively small and isolated fragments
Much work has focused solely on total species richness and using species–area relationships to determine the optimum size and configuration of habitat patches in order to maximize within-patch diversity (Margules et al 1982, Le Roux et al 2015). This approach overlooks these two key area-dependent effects: that the species–area relationships may hide a turnover of species, due to species composition altering with patch area, and that the function provided by the habitat patch to its species may alter with patch area, such that smaller patches with lower within-patch diversity may contribute to outside-patch diversity by providing just one function to non-habitat specialists (Spellerberg & Sawyer 1999)
This suggests better landscape-level conservation outcomes might be achieved by assessing community composition as a function of woodland area and managing each woodland appropriately for the avian communities that typically use woodlands of that size
Summary
Deforestation has reduced woodland cover in the UK to just 11% (Smith & Gilbert 2003) and much of this woodland consists of relatively small and isolated fragments. Much work has focused solely on total species richness and using species–area relationships to determine the optimum size and configuration of habitat patches (such as woodland) in order to maximize within-patch diversity (Margules et al 1982, Le Roux et al 2015) This approach overlooks these two key area-dependent effects: that the species–area relationships may hide a turnover of species, due to species composition altering with patch area, and that the function provided by the habitat patch to its species may alter with patch area, such that smaller patches with lower within-patch diversity may contribute to outside-patch (i.e. landscape-level) diversity by providing just one function to non-habitat specialists (Spellerberg & Sawyer 1999). This suggests better landscape-level conservation outcomes might be achieved by assessing community composition as a function of woodland area and managing each woodland appropriately for the avian communities that typically use woodlands of that size
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