Effects of riparian buffer strips on ground beetles (Coleoptera, Carabidae) within an agricultural landscape

1. Current restoration of stream and lotic freshwater systems to
‘good ecological status’ has focused on the creation of vegetated riparian buffer
strips. Yet, despite this constituting a major land-use change, surprisingly little
is known about the effects of these strips on riparian organisms. We investigated the effect that widespread adoption of buffer strips may have on activity
density, species diversity, and assemblage composition of ground beetles (Coleoptera, Carabidae).
2. Over 2 years, we sampled carabids from 41 riparian margins within two
river catchments in north-east Scotland. We compared three types of riparian
margin: unbuffered (i.e. ‘unimproved’), vegetated buffer strips, and wooded, the
latter acting as reference sites. A range of site parameters including characteristics of soil, water, and vegetation were recorded and the extent to which they
correlated with ground beetle assemblages was explored.
3. Catchment and treatment effects were detected on ground beetle activity
density and species diversity with unbuffered sites showing higher activity density and species richness. The assemblage structure differed according to catchment, treatment, and local characteristics. Multivariate analysis suggested that
soil and vegetation parameters and stream width, together with buffer strip age
and length were determinants of assemblage structure. Few riparian species
were found in large numbers.
4. This study shows that in intensively managed agricultural landscapes riparian buffer strips do not create the quality of habitat required by truly riparian
species. They do, however, provide habitat for woodland and stenotopic species
and with more careful planning could play a role in increasing habitat heterogeneity at a landscape scale.