Though New Zealand has 2,065 plant species which grow nowhere else on the planet, 22,000 non-native plants have also made the isles their home. Of those, 2,069 have become naturalized: they have spread out across the country on their own. There are more naturalized invasive plant species in New Zealand than native species. It sounds like the makings of an ecological disaster: an epidemic of invasive species that wipes out the delicate native species in its path. However, the number of documented extinctions of native New Zealand plant species is a grand total of three. American scientists Dr Dov Sax and Dr Steven Gaines argue that attitudes about exotic species are too simplistic. While some invasions are indeed devastating, they often do not set off extinctions. They can even spur the evolution of new diversity. “I hate the ‘exotics are evil’ bit, because it’s so unscientific,” Dr Sax said.