Impact of an invasive clonal herb on epigaeic invertebrates in forest remnants in New Zealand

This study determines the impact of an invasive herbaceous weed Tradescantia fluminensis on invertebrates within three lowland podocarp/ broadleaved forest remnants in southern North Island, New Zealand. Epigaeic invertebrates were sampled within three Tradescantia-infested plots and three non-infested plots at each of three sites using pitfall traps. The abundance of invertebrates was reduced in Tradescantia plots compared with non-Tradescantia plots if Collembola and Acarina, the two most abundant and variable orders, are excluded (647 +/- 123 (mean SE) compared with 1153 +/- 370), though this difference is not statistically significant. There was no difference if they were included (3897 +/- 2530 compared with 2505 +/- 1095). Five of the 23 orders collected were sorted into recognisable taxonomic units (RTUs). RTU richness was lower in Tradescantia plots compared with non-Tradescantia plots (39.7 +/- 5.5 compared with 51.7 +/- 8.9) though there was weak statistical support. Deirended correspondence analyses separated Tradescantia and non-Tradescantia plots within sites when based on RTUs, but not when based on orders/families. Overall, impacts of Tradescantia were apparent despite large differences in invertebrate assemblages among sites. The impact of Tradescantia could be a result of the weed's tall, dense vegetation structure and associated microclimate, relative to native ground covers. (C) 2003 Elsevier Ltd. All rights reserved.