Seeing the woods amongst the weeds: Weeding out Huramua Reserve

Huramua Reserve, freed from 890 kg
of weeds

You wouldn't think it possible, but its true - 890 kg of weeds were cleared from this "handkerchief" reserve near Wairoa, Hawke's Bay.

At just under 2 ha, Huramua Nature Reserve is tiny. In terms of conservation value though, it is more like a giant. Huramua Reserve is home to a healthy population of the nationally endangered shrub Pittosporum obcordatum. And a major weeding exercise is helping to keep them safe.

In October 2002 DOC staff members Helen Jonas and Bec Stanley, with volunteer Margaret Fraser visited the reserve for the first time in ten years to survey Pittosporum obcordatum. There was good news and bad news. The good news was that the population of Pittosporum obcordatum was alive and well; the bad news was that weeds were on the rampage, and without major weed work the future of the reserve was looking grim.

Japanese honeysuckle

Japanese honeysuckle was the main culprit and had clambered and spread through most of the reserve. Helen says this was by far the most difficult weed to control and fears that the devastating powers of Japanese honeysuckle have been underestimated, rating it in terms of environmental damage as "up there with old man's beard". Other weeds present included blackberry, hawthorn, privet, Chinese privet and pampas.

The Huramua challenge then, was to deal to these weeds without damaging the endangered Pittosporum; with such a small reserve any translocation of herbicide, spray drift or careless spraying could be disastrous. Rising to this challenge, Helen Jonas got a team of three on the job (2 WINZ contractors and a trainee ranger), and for two weeks last December the "Huramua Weeders" heaped trailers high with weeds.

Hawthorn berries

Weeds were taken to the local landfill where they weighed in at 890 kg. Most of the weeding had to be done by hand, and piles of Japanese honeysuckle, blackberry and hawthorn were laboriously hand-pulled. Cut stumps were carefully treated with Roundup, and some large hawthorn trees were drilled and Roundup poured into the holes. Privet and Chinese privet were all cut and stump-treated, and a big clump of pampas was cut and sprayed.

On-going weeding in this small but precious reserve is a must, and funds have been secured for half-to-a-day's weeding once every month with plans afoot for future planting of kahikatea, cabbage tree and kawakawa.

Tree privet

Small reserves are easy prey for weeds since their large amount of edge (margin) and relatively small area makes them vulnerable to weed invasion. Light-loving weeds such as Japanese honeysuckle have plenty of places to seed around the edge and to grow and climb to the canopy. Other reserve invaders such as hawthorn can make the most of any damage caused by the climbers and other disturbances and get a firm foot-in-the-door of the reserve. For Huramua Reserve, only the very centre was weed free - and this area has been fenced and undisturbed since the 1930s when it was protected as one of New Zealand's two known sites of the Pittosporum obcordatum.

The endangered Pittosporum
obcordatum

Pittosporum obcordatum is now known to occur from as far north as Kaitaia to as far south as Lake Manapouri. Throughout the country one of the main threats to the species is out-competition by weeds. The mammoth weeding effort at Huramua Reserve proves that this is not an insurmountable threat, but is certainly one that requires constant work.

Many thanks to Helen Jonas (Wairoa Field Centre) and Mike Thorsen (East Coast/Hawke's Bay Conservancy).

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