Patterns of terricolous and field layer invertebrates along a boreal mire-forest gradient

Abstract

In a study area ca. 5 km N of Umeâ, Sweden, we tested the relationship between abundance and biomass of terricolous and field layer invertebrate taxa along a light gradient (consisting of four different forest habitats of boreal coniferous forests, each represented by one stand). In 1984, five sampling locations, each having 6 pitfall traps and 3 sweep-net samples, were randomly allocated in each stand. In total, 4879 terricolous invertebrates with a biomass of 63 490 mg and 1894 field-layer invertebrates with a biomass of 17 143 mg were caught. Mean values for each sampling location were used to analyse the pattern of invertebrate groups along the gradient using Spearman rank correlation (n = 20). There was a decrease in both abundance and biomass from shaded to sunny forests of Diptera (both terricolous and field layer), Hymenoptera (terricolous), Collembola (field layer) and Lepidoptera larvae (field layer), and for the abundance of terricolous Coleoptera and field layer Hymenoptera. An increase in both abundance and biomass from shaded to sunny forests was found for terricolous Collembola, Homoptera and Acari, and the abundance of terricolous Formicidae and Coleoptera larvae, and the biomass of field layer Hymenoptera larvae and total invertebrates. Diptera, Coleoptera and, especially, Lepidoptera larvae have earlier been shown to be important prey for several bird species breeding in the boreal forest and the high number and biomass of these taxa in the shaded forest habitats may indicate that preserving buffer zones and fragments of wet, shaded forest, currently done in forest management at final felling, is a good strategy.