Importance of Sampling Along a Vertical Gradient to Compare the Insect Fauna in Managed Forests

Unbiased samples from insect traps are dependent on the placement of traps to account for variation in the spatial distribution of insect fauna. In forests, the spatial distribution of insects reflects forest vertical structure. However, comparative studies of insect diversity in managed forests have traditionally focused a single forest stratum (e.g., forest floor, canopy). We evaluated the importance of sampling along a vertical gradient to assess the effects of silvicultural treatments on insect fauna. We compared the catch from flight-intercept traps suspended at 1, 3, 5, 7, 9, and 11 m above the forest floor in eight forest stands representing three management types: two clearcut stands, two shelterwood stands, and four selection stands. The vertical distribution of insects was significantly different across the three management systems. A greater proportion of the insect fauna was recovered close to the forest floor in clearcut stands than in selection and shelterwood stands. Some insect taxa were restricted to the higher traps; whereas other taxa showed different height associations across the three management systems. Therefore, vertical sampling is important to compare the insect fauna in managed forests differing in vertical structure.