Weedbusting, summer 2016

mothplant-thumbOur Project Island Song summer weed-busting season on Urupukapuka finished at the end of April with the conclusion of Explore’s summer ferry service to Otehei Bay, and is now underway on Moturua.

The team continued to remove kahili ginger from the valley system behind the Otehei Bay resort and the south face of the ridge on the northern side of the bay. This is a prime area for regeneration of native vegetation because of good soil moisture levels along the valley floors and the shaded ridge slopes, as indicated by the ferns Blechnum novae-zelandiae (kiokio) and Deparia petersenii.

The ginger removal process in Otehei Bay began at the end of 2009 and ginger control is now a feature of summer weed busting. This season only five ginger flower heads were found; last season there were closer to 100, so we are getting on top of the flowering-size plants. Although there were very few seedlings, we had a lot of small old plants that apparently had been dormant for some time, but burst into growth with the warm wet summer and the increased light levels following removal of big old ginger plants. Each week saw another crop of these appear, and one of the group swears that a couple shot into growth during our lunch break!

There has massive regeneration of native plants in the sites cleared of ginger which can form dense clumps under which nothing can grow. Coprosma (several species), hangehange, kawakawa and mahoe are most common, with occasional totara, kowhai, puriri and towai appearing, all due to six years of weed busting.

Autumn to spring is Moturua time, particularly the species-rich Mangahawea creek surrounds, site of serious moth plant control since March 2012 and the only site on Ipipiri with native (non-planted) populations of kohekohe and puriri. In 2012 6700 moth plant pods were collected along the creek system – each pod has at least 500 seeds – and rotted down on-site in black rubbish bags. We are still dealing with the residue of seeds from pre-2012 moth plant crops, which can stay alive in the soil for at least 13 years, so frequent visits are necessary.

In addition to the creek area we have sites at the northern and southern ends of Mangahawea Bay (controlled from 2010 onwards) and one in Frenchman’s Bay (controlled from 2011 onwards). Fortunately, we have a grant for transport from QEII/Weedbusters which will get us out to Moturua more often in future.

Moth plant growth can be fast in these warm wet summer conditions. We did a clear-out of the lower Mangahawea creek on Moturua in November to get rid of all moth plants from seedlings to 4m-high climbers, yet by April another crop had taken hold.

However, there are fewer moth plants now and numbers of Mexican Devil, Cape gooseberry, tobacco weed and brush wattle seedlings have reduced after four years of intensive weeding. The creek system now supports a grove of young cabbage trees and sedges, with coprosma, kawakawa, hangehange, mahoe and whau seedlings.

May 2016 sees the return of Tim and Helen Armitage to Moturua, this time accompanied by daughter Emma, for their third blitz on pines, wattles, tobacco weed and moth plant. Their species-based approach to weeds is complementary to that of the site-based Project Island Song weed busters and there is good collaboration between us so that we are not targeting the same plants in the same area. Tim’s dead pines are now visible from out at sea – perhaps you have seen them as you sail past Moturua.

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Tags: Ecological restoration, Pest management

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