The importance of CWD for Insect Diversity

Posted by Darren Ward @nzhymenoptera

Trees are mostly made of woody stuff. Sometimes this stuff breaks and falls on the ground. It’s called coarse woody debris (CWD).

CWD is considered a ‘wasted’ resource if it just lies around in a forest. Not so! Overseas, the role of CWD has often been heavily studied for its role in restoration, succession, nutrient recycling, and in maintaining the diversity of invertebrates, fungi, et al. But this appears not to be the case for New Zealand, at least from an entomological perspective.

good cwd.png

Good use of CWD

bad cwd.jpg

Less good use of CWD

 

Some of our recent work had highlighted the entomological importance of CWD in forests in the Waitakere Ranges. Our broad aim has been to examine the abiotic factors affecting the diversity of invertebrates, and more specifically different groups of wasps, both native and exotic species.

In each of the studies completed so far, CWD has been a key factor in influencing insect diversity, both the number of species, and the functional diversity of communities.

For example, the abundance of parasitoid wasps in the subfamily Cryptinae, who predominantly attack wood-boring insects (e.g. the larvae of beetles, caterpillars), were positively associated with total CWD volume; while parasitoids that predominantly attack larvae on exposed surfaces such as leaves were negatively related to CWD volumes. Our results also suggest many parasitoid species (and their hosts) utilise small sized pieces of dead wood, indicating the importance of having a range of resources in an environment.

CWD also affects the community structure of spider-hunting wasps (Pompilidae), where greater CWD volume facilitates greater species richness; and specialist deadwood species are only present in areas with higher volumes of CWD.

However, CWD not only influences native insect communities. It also plays a role in regulating the density of an exotic wasp, Meteorus pulchricornis. Here, densities of this parasitoid declined with increasing coarse woody debris, suggesting some type biotic resistance mechanism where Meteorus pulchricornis is less able to invade native forests.

So CWD, it’s cool. Keep it. For the bugs.

Darren Ward is an entomologist in the New Zealand Arthropod Collection at Landcare Research, and a senior lecturer at the School of Biological Sciences, University of Auckland.

Kendall L, Ward DF. 2016. Habitat determinants of the taxonomic and functional diversity of parasitoid wasps. Biodiversity & Conservation. 25(10), 1955-1972i

Kendall L, Ward DF. The role of habitat variability in determining community structure of spider-hunting wasps (Hymenoptera: Pompilidae). Submitted!

 McGrath Z. 2017. Quantifying the ecological risk of exotic species–a case study using the parasitoid Meteorus pulchricornis. MSc Thesis, University of Auckland. Almost submitted!!

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