Bark beetle diversity at different spatial scales

To determine how the scale of observation affects ecological patterns we studied balk beetle (Colcoptera, Scolytidae) diversity in southern Finland. A block severing 160 x 160 m of a forest was delimited in four stands of different site types. Each block was divided into 256 squares (10 x 10 m) in which the occurrence of bark beetle species was recorded. In addition, environmental variables describing site type, trees, and breeding material appropriate for bark beetles were measured. The species presence/absence data were combined at different scales of resolution (10 x 10 m, 20 x 20 m, 40 x 40 m, 80 x 80 m, 160 x 160 m). At the finest scale a recently thinned pine stand showed relatively high diversity compared to other study stands due to a few evenly distributed and abundant species. However, the species diversity increased faster toward larger scales in mature spruce stands with several sporadically distributed species. According to logistic regression analyses, breeding material and site characteristics explained the occurrence of most beetle species. However, these variables did not explain the occurrence of the six most frequent species, probably because the factors regulating their distribution and occurrence operate at larger scales.