Permeability of protected natural areas to problem plants

Weeds are increasing in New Zealand's protected natural areas as the natural landscape is fragmented and land use intensifies. There are presently about 75 species that are considered to be problem weeds (Timmins & Williams, 1987). We attempted to determine the most important factors influencing the susceptibility of forest and scrub reserves to invasion by problem weeds. The data set was derived from 3 surveys of scenic and allied reserves: Auckland (Gardner et al., 1981); Taranaki (Clarkson & Boase, 1982); and Marlborough Sounds (Walls, 1984). Weediness was related to 14 reserve characteristics, using correlation coefficients and regression equations: size, shape, setting, i.e., surrounding land use, proximity to nearest town, proximity to railways and roads, presence of flowing water, soil fertility, fire history, presence of rubbish, proportion of woody vegetation, presence of clearings, stock use, and human use. About half the parameters are significantly correlated with weediness in at least one region. Results suggest the most important factors influencing the weediness of reserves are proximity to towns, and the setting. These are both a reflection of intensifying land use. The most vulnerable reserves are small, narrow remnants, with clearings, on fertile soils, and close to towns. These require close monitoring for plant species known to be problem weeds, and those whose weed potential has yet to be demonstrated.