A global view of the future for biological control of gorse, Ulex europaeus L.

Gorse (Ulex europaeus L.) has become naturalized in at least 50 countries outside its native range, from the high elevation tropics to the subantarctic islands and Scandinavia. Its habit, adaptability and ability to colonize disturbed ground makes it one of the world’s most invasive temperate weeds. It is 80 years since New Zealand first initiated research into biological control for gorse. This paper briefly reviews the progress made worldwide since then, and examines future opportunities for biological control of this weed. The range of available agents is now known, and this list is critically assessed. Ten organisms have been released variously in six countries and islands and their performance is reviewed. In most cases, agent populations have been regulated either from ‘top-down’ or ‘bottomup’, and there is no evidence anywhere of consistent outbreaks that could cause significant reduction in existing gorse populations in the medium term. Habitat disturbance and seedling competition are important drivers of gorse population dynamics. Existing agents may yet have long-term impact through sublethal effects on maximum plant age, another key factor in gorse population dynamics. Along with habitat manipulation, seed-feeding insects may yet play a long-term role in reducing seed banks below critical levels for replacement in some populations. In the short term, progress will rely on rational and integrated weed management practices, exploiting biological control where possible.