Long-term influence of forest management on Diptera abundance

Abstract

Intensive forestry practices, particularly clear-cutting, have significantly altered Norway’s forest landscapes since the mid-20th century. This shift away from traditional, more selective logging methods, has in many areas reduced the forest habitat connectivity and dead wood availability, which are known to be important for many insects. To understand the consequences from these forestry practices, it is essential to perform comparability studies between forest types.

In this study, Diptera were sampled using Malaise traps across 12 forest pairs in southeastern Norway to compare Diptera abundance between two forest types. Each pair consisted of one mature clear-cut stand and one near-natural forest stand. The samples were sorted, counted, and identified to the family level. They were also analysed both at the individual family level and collectively as total Diptera and saproxylic Diptera. Other potential predictor variables, such as dead wood volume, connectivity, period and weather variables were also measured. The results were analysed using a general linear mixed model (GLMM). The results revealed few differences in abundance between mature clear-cuts and near-natural forests, except for Phoridae, who were more abundant in mature clear-cuts. Dead wood was correlated only with the abundance of Tipulidae, while connectivity showed a correlation with saproxylic families as a group, as well as with some selected families.

To better understand the correlation between forest types and Diptera abundance, the study design could be improved using other trap types and an extended sampling period. Identifying Diptera to the species level is necessary, as broad ecological variation within many Diptera families can mask potential effects of forest type. Advances in DNA metabarcoding may offer a promising approach to overcome challenges in Diptera species identification.