Non-native trees profoundly alter the structure and resilience of native forest ecosystems through direct or indirect effects on ecosystem processes, e.g. by altering invertebrate communities, but such effects are poorly understood in New Zealand. We sampled adjacent stands of the non-native tree Douglas fir (Pseudotsuga menziesii) and native beech (Nothofagaceae) forests and tested whether the overall invertebrate communities varied across forest types.
The measurement of parasitism rates of wasp nests;lt Pelorus Bridge, New Zealand, at different distances from the initial release point suggests that the mean displacement of the parasitoid has increased by 1—1.5 km y(-1) from 1988 to 1993. Since average parasitism rates within this radius at any given site show little trend over time, this suggests an approximate 3-fold increase in the total parasitoid population each year, two-thirds of which is devoted to dispersal and one-third to maintaining local populations.