Insects and their habitat: dead wood.

The ConFoBi-project offers nice opportunities for students to work on their Bachelor’s or Master’s theses. I have already had the pleasure to supervise two ambitious Bachelor and Master candidates. One of their Bachelor theses studied how insect diversity is associated with coarse woody debris.

Of the approximately 11.000 species that occur in Central European forests, 20-50 % depend on dying or dead wood, for at least one stage within their life cycle. Half of these saproxylic species are currently endangered, as managed forests usually lack these habitat structures. Recently, forestry management practices have tried to increase the amount of dead wood of different dimensions and decay stages again (this is called retention forestry).

One of my tasks within ConFoBi is to investigate how the success of forest retentions measures is related to the landscape. Therefore, we set up two flight-intercept traps (see the previous blog entry on FIT) in each of our 135 forest plots in different landscapes with varying amounts of dead wood, and this to analyze diversity patterns of insects across the landscape. When planning this, I was curious whether two traps on each plot of 1 ha size would actually deliver a good measure of the insect diversity of that plot. Thus, we addressed this question (among others) in a Bachelor thesis.

One student distributed ten traps on one plot and then identified the captured Hymenoptera. She found 44 (morpho-) species of 16 families with 109 individuals. We found out that species assemblages differed strongly between each trap as most species were found in just one of the traps. Moreover, two traps represented on average only about 30% of the species that were captured by all ten traps.

Thanks to the students’ research we could conclude that the two traps that we set up on each forest plot are not  sufficient to depict the complete species richness that we may find in our research area. Nevertheless, even only two traps should capture more insects in forests with high insect activity than in forests with lower levels of insect activity. So, I am already quite excited whether differences in numbers of caught insect species correspond with dead wood amount and quality in forests and how this is also linked to the surrounding landscape. Let’s see what happens!

by Anna Knuff (B3)