Environmental Weeds In New Zealand: Impacts And Management

More than 25 000 plant species have been introduced to New Zealand, with 8.5% of those having naturalised so far, and an additional 20 species estimated to naturalise each year. Two-thirds of naturalised species were introduced as garden plants. The number of recognised environmental weeds in New Zealand has almost reached 400 species. Empirical impact data exists for less than 5% of our current environmental weeds, and these are almost all widespread or locally dominant species. The research that does exist has demonstrated a variety of negative impacts, ranging from reduced native species diversity, to altered nutrient regimes. However, management of weeds is more cost effective in the early stages of weed invasion, and there is rarely empirical impact research available at these stages of invasion. While it is not feasible to conduct empirical research on the impacts of all environmental weeds in New Zealand, the development of a comprehensive framework that evaluates known impacts would help inform timely weed management decisions.