New Weed Naturalisation Checklist For New Zealand
The fifth installment of the triennial “Checklist of dicotyledons, gymnosperms, and pteridophytes naturalised or casual in New Zealand” (Heenan et al. 2008) is now available in the June issue of the New Zealand Journal of Botany (45: 257-283 (2008)). In that paper the authors now accept six exotic species (Japanese wax tree (Toxicodendron succedaneum), Hydrocotyle bowlesioides, Geranium gardneri, Oxalis chnoodes, and plane tree (Platanus ×acerifolia)) as fully naturalised – notably – two of these are trees that have escaped from cultivation. A further 162 exotic taxa with “casual status” are recorded as establishing in New Zealand. Casual Status is further subdivided using a new classification scheme developed to reflect the weed establishment process. The new categories are: Cultivation Escape, Spontaneous Occurrence, Garden Discard and Intentional Release.The new classification scheme has been in development for several years. The intention is to document the degrees of exotic plant establishment to provide better information on future weed threats, the ways by which weeds enter our countryside and spread, and the degree to which they may threaten our “natural” environment. The authors developed the system to reflect that weed colonisation is ongoing, and so it is vital that botanists document any exotic plant establishment, be it seedlings germinating under the parent plant in a garden, to plants appearing “spontaneously” well outside the range of cultivation. Disturbingly the authors saw a need for another category “Intentional Release” to reflect that individuals and some plant societies appear to have been responsible for the ill informed and deliberate attempted establishment of exotic plants.
The new checklist admits 10 new exotic ferns, three conifers, and 149 dicotyledonous plants to the ever growing naturalised New Zealand Flora. The main source of all these weeds remains garden plantings. Of course these figures pale when the naturalised monocotyledonous flora is considered – an update on weedy monocots is long overdue, the last listing being that in Flora 3 published in 1980!
Reference
Heenan, P.B.; de Lange, P.J.; Cameron, E.K.; Parris, B.S. 2008: Checklist of Dicotyledons, gymnosperms, and pteridophytes naturalised or casual in New Zealand: additional records 2004–06. New Zealand Journal of Botany 45: 257–283.
Posted: 11/08/2008