Hauturu – War on weeds

Pest weeds are often the ones that produce thousands of tiny seeds borne on the wind or dropped by birds. Some seem to be able to thrive under any conditions, even surviving digging out or spraying with weed killer. Many weeds are garden escapees that have naturalised or those brought with a purpose in mind; think of gorse brought by Scottish settlers to make farm hedges and now covering hillsides throughout the country.

The issue with weeds is not just interfering with productivity in gardens, horticultural and farm land, but also in our native forests, wetlands, alpine and coastal landscapes. By their very nature they are vigorous, productive growers that can soon out-compete our unique native plant species by taking up space and nutrients. By displacing native plant species there is the roll-on effect on native animals and insects, whose important food source or hiding place is no longer growing in sufficient numbers.

On Te Hauturu o Toi (Little Barrier Island), with its healthy balanced ecosystem and without mammalian pests, such as rats or possums, that can also affect vegetation health, there is still opportunity for weeds to establish, particularly in vulnerable open spaces like coastal cliffs and stream edges or slip faces. Over the years most of the non-native plants that were around areas of human habitation on the island have been removed or reduced in number. A weed management programme was begun in 1996 by the Department of Conservation. This was reviewed and expanded in 2004 with the aim of eradicating some 37 targeted weeds.

The main problem weeds on the island now are pampas (Cortaderia spp), a relative of our native toetoe (Austroderia splendens). Pampas is recognisable by its more upright flowering heads, either cream or purple, and slightly later flowering time than the October to late January of the graceful, creamy toetoe. To work towards eradicating pampas on the island, it was initially necessary to use helicopters and weed spray on the inaccessible cliff faces and slip sites. Now ground teams removing young plants can accomplish some of the work. The seeds are wind blown, so there is the high chance of reinfestation from the mainland or other gulf islands. A simple way we can all reduce the spread of pampas is to cut off the flower heads before seed forms.

Climbing asparagus (Asparagus scandens) is the other main weed of concern. Birds commuting to the mainland can return with bellies full of illicit seeds. This weed is of particular concern as it can grow in the dim light of the forest and strangle the understory (plant life growing underneath the canopy), transforming the forest. Several sites have been found on cliffs and have required the expertise of abseilers to remove the plants by hand to make sure the tuberous roots are also removed. Again, if you know of sites on the mainland, removing plants before they fruit in the autumn will greatly help to reduce the spread.

The Little Barrier Island/Hauturu Supporters Trust has assisted this weed programme by sourcing funding from Foundation North, DOC’s Community Conservation fund and Chisholm Whitney Family Trust. Fiskars have provided tools for the team and Nufarm have donated some necessary chemicals.