Effect of distance to urban areas on saproxylic beetles in urban forests

Abstract: Urban forests play key roles in animal and plant biodiversity and provide important ecosystem services.  Habitat fragmentation and expanding urbanization threaten biodiversity in and around urban areas.  Saproxylic beetles can act as bioindicators of forest health and their diversity may help to explain and define urban-forest edge effects.  I explored the relationship between saproxylic beetle diversity and distance to an urban area along nine transects in the Västra Götaland region of Sweden.  Specifically, the relationships between abundance and species richness and distance from the urban-forest boundary, forest age, forest volume, and tree species ratio was investigated Unbaited flight interception traps were set at intervals of 0, 250, and 500 meters from an urban-forest boundary to measure beetle abundance and richness.  A total of 4182 saproxylic beetles representing 179 species were captured over two months.  Distance from the urban forest boundary showed little overall effect on abundance suggesting urban proximity does not affect saproxylic beetle abundance.  There was an effect on species richness, with saproxylic species richness greater closer to the urban-forest boundary.  Forest volume had a very small positive effect on both abundance and species richness likely due to a limited change in volume along each transect.  An increase in the occurrence of deciduous tree species proved to be an important factor driving saproxylic beetle abundance moving closer to the urban-forest.  Overall, analysis showed inconsistent effects on both abundance and richness as functions of proximity to the urban-forest boundary.  Urban edge effects, forest volume, forest age, and forest tree species make up are all variables that may effect saproxylic abundance and species richness.  Forest managers should consider these variables when making management decisions.