Weeds, weeds, weeds

Howell, C. 2008. Consolidated list of environmental weeds in New Zealand. DOC Research & Development Series 292, Department of Conservation, Wellington, New Zealand.

Clayson Howell of the Department of Conservation (DOC) has compiled a useful list of all the 328 vascular plant species that DOC regards as environmental weeds, and which are actively controlled on DOC-managed wildlands.

As Clayson writes, "New Zealand is a very weedy place" (p. 4). It's likely to become more so. It's well known now that naturalised exotic vascular plants in New Zealand have outnumbered native plants. There is something over two thousand native vascular plant species in New Zealand, almost all endemic (it's 2158 species according to de Lange et al.'s 2006 New Zealand indigenous plant checklist, published by the New Zealand Plant Conservation Network). Howell and Sawyer (2006, New Zealand naturalised vascular plant checklist, published by the New Zealand Plant Conservation Network) recognise 2391 naturalised exotic species. With DOC now managing 348 of these as weeds, that's 13% of New Zealand's naturalised plants that are nasty enough to justify control as environmental weeds. I recently combined the DOC list with all plants listed as pests on the Regional Council's various pest management strategies (RPMS), to get about 400 species. Add on that weeds being controlled by agriculture, horticulture, and forestry (plus private gardeners), and it is becoming clear that ecologist's "Tens Rule" of about 10% of naturalised plants becoming weeds (and 10% of introduced plants naturalising) is looking increasing optimistic for New Zealand.

While most of the report is a species list, Clayson also provides a useful overview of where and why these species are regarded by DOC as weeds, when they were first discovered in NZ, and an overview of which lifeforms are over- and under-repesented as weeds from the full naturalised flora.

The report is available from http://www.doc.govt.nz/upload/documents/science-and-technical/drds292.pdf (278 KB).