Birds and insects respond differently to combinations of semi-natural features in farm landscapes

Semi-natural features among farmland have a key role in maintaining
wildlife in rural landscapes. Practical conservation requires knowledge of
which combinations of features are of greatest value and whether this
differs among faunal groups. We used a ‘landscape’ approach to investigate
the relative importance to birds and insects (bees, flies, wasps) of
combinations of three wooded features typical of farmland in south-eastern
Australia: scattered trees, wooded roadsides and wooded streamside
vegetation. We selected 44 landscapes (1 km diameter) representing four
combinations: a) landscapes with all three features present, b) landscapes
lacking scattered trees, c) lacking wooded roadsides, and d) lacking
wooded streamsides. We surveyed birds and selected insects, and compared
mean alpha (α, site), beta (β, between site) and gamma (γ, landscape)
diversity for each taxon between landscape types; and gamma (γ) diversity
of bird species displaying breeding activity. Mean α-diversity of birds
was reduced in landscapes lacking wooded roadsides or streams, relative to
those with all three wooded features; while species differentiation
(β-diversity) increased in these landscapes. Loss of streamside vegetation
had the greatest landscape-scale impact, reducing γ-diversity by ~33% for
all land-birds and ~50% for woodland birds. Bird breeding activity
declined by ~50% in landscapes lacking wooded streamsides. In contrast,
insects showed little response, except bees for which mean α-diversity was
greater in more-open landscapes lacking scattered trees or wooded
roadsides, compared with those containing all wooded features. This did
not lead to differences in landscape-level (γ) diversity. Synthesis and
applications. Marked differences in how birds and insects respond to
different combinations of semi-natural features mean that a ‘one size fits
all’ approach to nature conservation is insufficient. Wooded features,
especially streamside vegetation, are critical for maintaining diversity
and breeding activity of woodland birds. In the absence of adequate
knowledge of many insect groups in southern Australia, a prudent approach
is to foster a diverse farmland mosaic comprising semi-natural habitats
together with floristically rich, modified features that provide
temporally dynamic resources. Small semi-natural features have
disproportionate value for conservation, relative to their area, while
also benefitting farm productivity and supporting ecosystem
services.