Scott Lassau
M.Sc. (Env) 1999
Roads and their edges form major barriers to the movement of terrestrial fauna
and disrupt local species distributions. Studies of edge effects to date have
often lacked controlled, quantitative sampling. This study examined the effects
of road edge and traffic density on abundance of small mammals and the abundance,
species richness and species composition of invertebrates in the Hornsby Shire
of New South Wales, Australia. The need for such a study was introduced by an
analysis of shortcomings of the methodology used in recent major road Environmental
Impact Assessments in New South Wales.
Nine sites representing three replicates of three different road types were sampled, using a trapping grid with five individual transects, extending from 0m to 200m from each road. Live trapping and pitfall trapping survey methods were used for small mammals and invertebrates, respectively. Effects of road type were evident during at least one trapping period for both Antechinus stuartii and Rattus fuscipes, significantly greater abundances of each occurring at control roads than experimental roads. There was a general increase in small mammal abundance with increasing distance from the road edge, the significant effect of distance being within 100m and 200m for A. stuartii and R. fuscipes, respectively, suggesting both species prefer interior habitat.
The species richness of ants was highest at the road edge, lowest 25m from
the road edge, then increased steadily to 200m. The abundance of ants was significantly
greater at traffic free experimental sites (bushroads) than at either controls
or high traffic density sites. Beetle species richness generally increased with
increasing distance from high traffic-density roads. No trends existed in spider
abundance nor species richness. High traffic-density sites contained a significantly
less homogenous ant and combined target taxa species composition than bushroads
or control sites. The ant species Rhytidoponera metallica and Iridomyrmex sp.
showed the most dissimilar distribution patterns with respect to road edge distance,
suggesting they are edge and interior specialists, respectively.
If the effects of road edge from this study are taken into account, a nature
reserve, if surrounded by roads consisting of traffic, or nature corridors between
roads, must be at least 400m x 400m to allow suitable living habitat for all
fauna surveyed in this project. Road edges rendered effects on fauna operating
at different spatial scales, implying an influence on several components of
ecological communities in the Hornsby Shire of New South Wales. Environmental
managers need to consider the implications of edge effects before making decisions
regarding the impacts and mitigative measures of anthropogenic disturbances
such as road construction.