Prioritising local habitat quality for woodland hoverflies

Kirsty Park and colleagues discuss the importance of habitat quality in restoration efforts. Read the full article, Local-scale attributes determine the suitability of woodland creation sites for Diptera in Journal of Applied Ecology.

To benefit woodland-associated Diptera, and in particular hoverflies, woodland creation and restoration efforts should focus on ‘habitat quality’, in particular to ensure a diverse tree and understory vegetation structure. These are the findings of a new study in Journal of Applied Ecology which surveyed hoverflies and craneflies in 78 secondary woodlands created over the last 160 years in England and Scotland.

Diptera, or true flies, the group encompassing hoverflies and craneflies, may not be what managers have in mind when planting a new woodland, or trying to restore a degraded one. However, the larvae and adults of these insects play an important role in the ecosystem through performing functions such as decomposition and pollination. Whether a species can colonise a new woodland, and whether it can persist once established, is likely to be influenced by the characteristics of both the woodland itself and the wider landscape, as well as by the dispersal ability of the species. This study set out to examine the relative importance of woodland characteristics (such as the woodland age, area of woodland patch, tree species richness and variation in tree size) and the landscape (such as the amount and connectivity of surrounding woodland). Hoverflies and craneflies were chosen because of their associations with woodland and differing dispersal abilities.

Through repeated surveys at the same sites the authors detected a quarter of British woodland hoverfly species and almost half of all British woodland cranefly species in the study sites, indicating that woodland insects are colonising created native woodlands, despite their small size (sites averaged 3.3 ha) and fragmented nature. Unsurprisingly, they also caught large numbers of agricultural and grassland species which are more closely associated with the surrounding landscape. The high mobility and low abundance of hoverflies could mean many of the species found were just passing through the woodland. Woodland cranefly species were more abundant than hoverflies, possibly because their low mobility which makes them very dependent on small-scale woodland microhabitats and more confined to the woodland interior. Whilst craneflies did not appear to be influenced greatly by woodland or landscape characteristics, hoverflies responded positively to variation in tree size and amount of understorey cover. The authors do acknowledge, however, that the landscape context of these woodlands may be important for other Diptera that have yet to reach these new woodlands.

This study is part of a wider long-term collaboration called the WrEN project (Woodland Creation & Ecological Networks) which uses a natural experiment approach to assess the impact of past woodland creation on current biodiversity. To date the team, comprising academics, practitioners and policy makers, have surveyed 106 secondary woodlands and 27 ancient woodlands for a wide variety of taxa including lower plants, vascular plants, small mammals, bats, birds and invertebrates. Analyses have been completed for foraging bats and breeding birds, and the WrEN team will be publishing a multi-taxa synthesis in due course.

Read the full article, Local-scale attributes determine the suitability of woodland creation sites for Diptera in Journal of Applied Ecology.

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