Activity-densities of ground-dwelling invertebrate assemblages in the transition zone between adjacent conifer and hardwood forests

The effects of forest edges adjacent to open lands are well established. However, knowledge about the edges between two different forests, which represent relatively smaller changes in microclimatic conditions due to continuous canopy cover, is limited. Here, we investigated the activity-density of ground-dwelling invertebrates across the zone between conifer and hardwood forests. Most of the major invertebrate groups (Coleoptera, Formicidae, Prostigmata, Gamasida and Oribatida) were more active in the hardwood forests than in the conifer forests, and none of the groups revealed higher activity-densities in the conifer forests than in the hardwood forests. Especially, Formicidae and Prostigmata decreased their activity-densities from the forest edges towards the interior parts of the conifer stands. These suggest that many invertebrates leak from the hardwood to the conifer forests. We indicate that the responses of the major invertebrate groups to the distance from forest edges towards the interior of conifer or hardwood stands were taxon-dependent. Our findings suggest that forest edges between the conifer and hardwood forests were not distinct boundaries for ground-dwelling invertebrates unlike the aboveground vegetation structure. However, the conifer plantations adjacent to hardwood forests hinder the dispersal of some invertebrates to other hardwood habitats. Therefore, the continuity of hardwood forests should be taken into account for the conservation of forest biodiversity.