Vertical stratification of scolytine beetles in temperate forests

Although most studies exploring the vertical distribution of arthropods in forests have been limited to discrete comparisons between understorey and canopy, few have sampled across multiple heights. We studied vertical distribution of scolytine beetle flight activity in temperate lowland broadleaf and montane beech-fir forests using flight interception traps arranged in vertical transects with traps placed 0.4, 1.2, 7, 14, and 21 m above ground. In each forest type 15 vertical transects (75 traps) were used. The assemblages sampled at 0.4 and 1.2 m above ground (undergrowth) clearly differed from those at 7, 14, and 21 m (midstorey and canopy). Ambrosia-fungi feeder abundance peaked at 1.2 m in the mountains, whereas in the lowland they were almost evenly distributed from 1.2 to 21 m. Phloem feeders were significantly more abundant in the midstorey and canopy than in the undergrowth. Height preferences of eleven species were identified. Four species were associated with traps exposed at 7, 14, or 21 m, whereas seven species were associated with the height of 1.2 m. No species was associated with the 0.4 m height. To cover entire scolytine assemblages of forest stands, sampling should thus not be restricted to the usually sampled understorey level, but also cover the canopy.