"I think we're in danger of losing what has been a very high reputation for environmental management," he said.
Some northern hemisphere countries such as Norway, with "very impressive landscapes" and an "impressive record in environmental management", were already promoting themselves as positive visitor destinations.
As environmental awareness grew, potential tourists could perceive such countries as requiring fewer "pollution miles" to reach via air travel, by comparison with New Zealand, he said.
Prof Mark (78) said New Zealand's international clean green image was "a good sales pitch" but many "insufficiencies and deficiencies" also needed to be addressed.
New Zealand had achieved some important conservation successes, such as establishing 10 high country conservation parks, but more work was needed.
Prof Mark, of the University of Otago botany department, was last year awarded the 2010 Charles Fleming Award for Environmental Achievement from the Royal Society of New Zealand.
In announcing the national environmental science award, Royal Society officials said Prof Mark was "regarded as New Zealand's leading environmental scientist and conservationist".
During his long research career, Prof Mark had "explored and illuminated the ecology of southern ecosystems", including tussock grasslands and wetlands, society officials said.
As part of the national award, Prof Mark has become the Charles Fleming Lecturer for 2011 and at Otago University this week he gave the first of a series of lectures to be given throughout the country.
The talk focused on "mountain tops to ocean depths" and considered his "involvement with a range of ecological/environmental issues, mainly in the south".
Prof Mark, who has also been awarded the society's Hutton Medal, described a lifetime involvement with "pure and applied ecological studies" of indigenous upland snow tussock grasslands, mostly with the Hellaby Indigenous Grasslands Research Trust.
He said he was concerned about mooted cuts to Government funding for the Department of Conservation and said New Zealand could not afford to rest on its laurels if it was to maintain its positive international image.
Asked about New Zealand promoting itself abroad as "100% pure", he said more work was needed to improve the water quality of streams and rivers, and to address water abstraction issues.
New Zealand's endemic bird populations were in a "very critical state" and it was a "sad reflection on the rest of the country" that some endangered New Zealand animals were fully protected only in small sanctuary areas, such as the Orokonui Ecosanctuary near Dunedin, he said.
Prof Mark has served as a government appointee on several conservation bodies and is deputy director of the Temperate Grasslands Conservation Initiative of the International Union for the Conservation of Nature.
