Weed threat to native species

Rod Butcher Photo/File

Last week I had a visit from the Horizons pest plant manager. I showed him the problem weeds I have here on my 4ha lifestyle block at Aramoho. These weeds include old man's beard, field horsetail and Elaeagnus. His main concern is old man's beard which is epidemic in Aramoho.

I showed him how I had "cleaned up" half the block in my 13 years' residence here and felt confident about dealing with the rest.

Of all these obnoxious weeds, however, the plant that I find the most daunting is karaka (Corynocarpus laevigatus). This tree is very firmly established on my block, and I do not think I can control it.

The crazy part is it is still being sold as an attractive garden tree in nurseries and plant shops. Karaka is thought to have been introduced to the country by early Maori settlers and is not endemic here. The large, orange fruits are highly toxic to humans and have cost many lives and deformities in Maori children in the past.

Karaka has been banned in many Pacific islands, where it is superseding their native species. I believe we must act urgently to protect our native bush from this species, I think the karaka will become the "possum" of the plant world.

I cut down several mature fruiting karaka here three years ago, but there are still several mature trees growing on inaccessible faces that the pigeons feed on each year. Every year a fresh "carpet" of glossy, 100mm-high seedlings covers the bush floor, smothering out all other species. They can grow to 2m high trees in two years. I have spent a lot of time pulling up these seedlings, but I am losing the battle and now many are too big to pull out and have to be lopped off.

Apparently native pigeons have learned how to digest the harmless fruit covering and eject the stone, which is the toxic part. This ensures a steady supply of fertilised seed distributed all over the forests.

So I am definitely losing the battle against karaka.

When I came here 13 years ago, the bush areas were all badly infested with old man's beard, Elaeagnus and Japanese honeysuckle, which formed a dense mat over the top of the mahoe and kawakawa scrub.

I have managed to clean up about half of the block and have yet to tackle the remaining two hectares or so.

This work is highly rewarding with the beautiful transformation of the native species that quickly follow. Native seedlings soon miraculously appear, like the quick-growing pigeon wood and ribbon wood.

This all depends, of course, on my being able to control the karaka.

Rob Butcher is a conservationist, retired engineer and beekeeper.