Under which conditions does retention harvesting support ground beetles of boreal forests?

Forestry is currently undergoing a paradigm shift from clear-cut, even-age timber-production model toward a model that is based on spatially and temporally complex natural disturbances and structures, i.e., disturbance-based management model. This model involves a variety of logging methods, high level of green-tree retention, better consideration of legacy elements, and modifications of density, age and species structure of harvested forests. Many characteristics of this model have been studied using boreal ground beetles (Coleoptera, Carabidae). These are mostly short term (up to 10 years after logging) and conducted at spatial scales of within or between stands. Compared to "classic" clear-cutting, modifications of it - green-tree retention and decreasing clear-cut size - positively affect closed-forest species and attenuate the increase of canopy-closure generalists and open-habitat species. Thresholds in carabid response occur at 40-50% retention (trees/ha), below which closed-canopy specialists start to quickly decrease, and at 20-30%, below which open-habitat specialists drastically increase. Selective logging in principle creates gaps of up to ca. r = 5 m through removals of single trees and does not significantly affect forest carabids, assuming >60% retention. However, >0.1-ha clear-cut gaps (ca. r = 10 m) may face rapid changes in species composition: the larger the gap, the larger the change. Forest carabids also generally benefit from retention of patches of subdominant species and wet bogs, and increased downed dead wood. Notable knowledge gaps in carabid research in the boreal region exist particularly on large-scale responses of carabids to forestry, especially specific responses of arboreal species, and carabid responses to forestry in rare habitat types, such as groves, pine heaths and forest streams. Long-term studies would be extremely valuable now, considering the many rapid global-scale climate and land-use changes.