Stand type is more important than red wood ant abundance for the structure of ground-dwelling arthropod assemblages in managed boreal forests

Abstract

1 The relationships between red wood ants (Formica rufa group) and other ground-dwelling arthropods were studied in young managed forests stands in Eastern Finland. The main objectives were: (i) to test the influence of stand type (dominant tree species; age: sapling versus pole stage) and numbers of red wood ants on the occurrence of other ground-dwelling arthropods and (ii) to study the occurrence of red wood ants versus other arthropods on a distance gradient from ant mounds. We used pitfall traps set in 5–14-year-old sapling stands and 30–45-year-old pole-stage stands of Scots pine (Pinus sylvestris L.) and birch (Betula spp.) forests. 2 Pitfall trap catches of red wood ants did not vary significantly between the forest stand types, although some groups of other arthropods showed clear responses to stand type (e.g. catches of other Formicinae and Gnaphosidae were higher in sapling stands than in pole-stage stands). The number of red wood ants clearly explained less of the variation in assemblages of other ground-dwelling arthropods than the forest stand type. 3 Red wood ant numbers decreased significantly with distance from the mounds, but the other ground-dwelling arthropods were insensitive to this gradient or even showed a preference for proximity to ant mounds and high ant activity. 4 The results obtained in the present study suggest that wood ants do not have strong effects on several other ground-dwelling arthropod groups in young managed forests other than in the immediate vicinity of their mounds.