Impacts of the weed Tradescantia fluminensis on insect communities in fragmented forests in New Zealand

The impact of the weed Tradescantia fluminensis on insect communities, as represented by Malaise-trapped beetles (Coleoptera) and fungus gnats (Diptera: Mycetophilidae s. l.), was studied in three forest fragments. Each fragment contained three plots with and without a dense weed cover. Data on vegetation and habitat variables were collected. Twinspan and Decorana analyses separated the plots by fragment for fungus gnat communities, and nearly so for the presence/absence of beetle species. The fungus gnat communities separated into plots with and without tradescantia at two sites, and there were fewer species of fungus gnats and beetles in tradescantia plots at the site with the simplest habitat structure. The richness of beetle and fungus gnat species was correlated with vascular plant richness. As tradescantia is known to prevent regeneration of many native plants, we predict a corresponding decline in invertebrate diversity and fragment complementarity where the weed is established.