DISTRIBUTIONS AND CLIMATIC CORRELATIONS OF SOME EXOTIC SPECIES ALONG ROADSIDES IN SOUTH ISLAND, NEW-ZEALAND

A survey was made of the distribution of twenty-four exotic species along roadsides on South Island, New Zealand. All species could be correlated to some degree with climatic factors, though for several species, alternative, correlated environmental factors gave almost as good a fit. Four species occurred in the colder/wetter areas (e.g. Cirsium palustre); the majority were more frequent in the warmer/drier areas (e.g. Lactuca serriola). Some species were confined to small areas with high summer temperatures, sunshine, and water deficit (e.g. Onopordum acanthium). Several pairs/trios of species correlated best with the same factors (e.g. Marrubium vulgare and Navarettia squarrosa with water deficit), though rarely were the species distributions the same in detail. There was usually some discrepancy between distribution and the best-fitting climatic factor. Possible reasons are discussed, including possible inaccuracy of published climate maps, and for four species the possibility that the distributions reflect dispersal limitations. Comparisons with the distributions of the species in their native ranges gave close agreement in climatic limits for some species (e.g. Echium vulgare, Onopordum acanthium, Senecio jacobaea), but considerable differences for others (e.g. Verbascum virgatum). Correlations were generally reasonable for Britain, but poor for continental Canada.