Relationships between insect diversity and habitat characteristics in plantation forests

A methodological approach to the identification of biodiversity indicators in commercial forest stands is illustrated by analysis of the relationships between syrphid (hoverflies) and carabid (ground beetles) community compos ition and diversity, and stand structure and field layer vegetation. Data w ere collected from 12 commercial forest sites encompassing a range of clima tic conditions and different crop types (Scots pine, Sitka spruce, Norway s pruce and Corsican pine) across the UK. Comparisons were also made between unmanaged semi-natural Scots pine woods and Scots pine plantations. For bot h syrphids and carabids, no differences in species richness and diversity w ere recorded between semi-natural stands and plantations; one rare syrphid considered to be restricted to semi-natural pine stands was also found in s pruce. Syrphid species diversity and richness was higher in southern spruce sites than in the northern sites. Northern sites had distinctive carabid c ommunities, as did sites in the New Forest, a large ancient woodland in sou thern England. Of the measured habitat variables, vertical stand structure showed the best correlation with species richness and diversity of both car abids and syrphids. Richness and diversity were less in stands with high ve rtical cover values for canopy layers. Stands with higher field layer cover supported greater syrphid diversity, but lower carabid diversity. Measures of stand structure could be used as potential indicators of syrphid and ca rabid diversity, but additional habitat parameters also need to be tested. (C) 1999 Published by Elsevier Science B.V. All rights reserved.