By Graeme La ****, Technical Advisor (Ecology)
DOC and the New Zealand Army recently held a field day to share information about one of New Zealand’s rarest and least understood ecosystems – the volcanic dunes of the Central Plateau.
What are New Zealand’s volcanic dunes?
Volcanic dunes comprise drifting sand derived from volcanic deposits that accumulate on volcanic ring plains during major eruptions and are then reworked by wind and water. This results in a chaotic assortment of mounds and hollows on a matrix of flat gravels, whereas coastal dunes have a linear sequence of crests and swales.
The only site in New Zealand where volcanic dunes occur is on the Central Plateau of the North Island, where they cover around 3000 hectares of the Rangipo Desert, or Onetapu (Maori for ‘forbidden sands’).
Actually they’re pretty rare around the world, with a cluster of sites on the west coast of the USA down to Mexico, and in Peru, Hawaii, Iceland, and Indonesia.
Why are the dunes of interest to DOC?
DOC’s interest in the dunes stems from the need to manage the northern end of the dunefield, which occurs in part of Tongariro National Park. The rest of the dunefield is in the Waiouru army training ground.
The field trip
The New Zealand Army and its new environmental manager have taken a renewed interest in the management of the dunes, so it made sense for us to get together recently on site to discuss the functioning of the dunes and future management.
After a few attempts we finally managed to find a day when the main body of dunes weren’t being used for Army training. Twenty of us gathered in an old house behind the Army Museum for an information day.
The group included biodiversity planners, rangers, visitor centre staff, technical staff from DOC, range control, environmental staff from the Army, invited speakers and a rehabilitation and coastal dunes expert. After we all crammed into Range Control for a safety briefing by Major Patrick Hibbs, he led our convoy into the dunefield.
Philosophical debates (such as why it’s a desert if it has two metres of rainfall a year, and whether it really is a dunefield) were mixed with practical discussions. Major Hibbs outlined the army’s use of the site; Mark Smale discussed the age, vegetation and ephemeral nature of the dunes; Angelina Smith spoke about the impacts of vehicles on the desert; and Alison Pickett spoke about the army’s management of weeds, particularly wilding pines.
We ended with a discussion on whether we should be re-vegetating the dunes near Tukino Road. It was evident from research and past attempts that trying to establish vegetation on the dunes, particularly red tussock, was a fruitless exercise, and that efforts should rather be put into limiting damage by vehicles and rabbits.
Overall the feedback on the day was very positive. Everybody seemed to learn something. Major Hibbs appreciated the opportunity to get out with experts, and to share his knowledge gathered over many years on the site. The biodiversity planners have a lot more information on which to base prescriptions, and for some people the idea that revegetation is a last resort, not a quick fix, came as a bit of a surprise.
Bill Fleury has even speculated on whether Logania depressa, a presumed extinct plant known from its first and only collection by William Colenso in the vicinity in 1847, may have been from this habitat. So there was plenty to pique our interest. I’m particularly pleased that visitor centre staff and hut wardens will have some new information to share with visitors.