Weed numbers in New Zealand's forest and scrub reserves

New Zealand's protected natural areas are being increasingly threatened by weeds as the natural landscape is fragmented and surrounding land use intensifies. To assist in designing management to reduce the threat, we attempted to determine the most important reserve characteristics influencing the presence of problem weeds in forest and scrub reserves. Data on 15 reserve characteristics were derived from surveys of 234 reserves. From correlation analysis, analysis of variance and consideration of several multivariate models, it appears that the most important characteristics influencing the number of problem weeds in reserves are proximity to towns, distance from roads and railway lines, human use, reserve shape, and habitat diversity. These factors reflect principally increased proximity to source of propagules associated with intensifying land use, including urbanisation. Reserves with the most weeds are narrow remnants on fertile soils with clearings and a history of modification, and those close to towns or sites of high human activity. If these reserves are to continue to protect natural values, they will require regular attention to prevent the establishment of further weeds. Accidental spread of weeds and disturbance in reserves should be minimised.