Diario del proyecto Gahnia Grove - Umbrella Project

The kikuyu within the original project area, ie the Annexe, Apron, Arena, Cape Honey Flower Bank, and from the outer edge of those areas along the mown kikuyu adjoining them, was eradicated by June 2019. Ingrowth from the mown sward has been suppressed since then by a number of experimental methods to try and find the most labour-efficient.

The remains of the 3 cu m of wood chip mulch applied to this edge in December 2018 have been instrumental in controlling new growth, but a deep layer of mulch seems to encourage the formation of deep rhizomes forcing underground into the cleared area. At present these are few, and have been suppressed, but until the development of dense shade along the margin they will continue to occur.

New surface runners can be lifted quite easily at a certain stage, and allowed to continue growing unrooted, for later pullback and self-rotting as alternate ground cover develops, eg exotic herbs. Mulch is thus being removed from the outer edge in order to allow ingrowth to be superficial and esily uprooted, rather than by deep rhizomes. Over the summer we shall see if this has the intended effect, and whether shade by exotic herbs develops soon enough to control the ingrowth by this method.

While this undesired mulch remains nearby, it can be used to assist with the composting, rather than drying, of any long unrooted material.

Therefore kikuyu will now appear within the cordoned area, being controlled experimentally at differing stages according to the degree of shade and competition provided by the exotic and native herbs and native trees as they develop.

From August to October 2019, release of about 40 m adjoining forest margin to the North from honeysuckle in the trees has required simultaneous control of honeysuckle on the ground beneath them, so this adjoining margin has been included in the trial of manual kikuyu edge control. There is no wood chip mulch here, but there was a lot of mulch provided by pullback of honeysuckle and kikuyu, and oxtongues and wild carrot are so far providing dense shade at ground level.

This provides the opportunity to trial and assess the effectiveness of strategies for manual control of kikuyu edge without wood chip mulch, and surrounding different tree species.

(UPDATE June 2020... few or no deep rhizomes emerged inside the Trial area since the above intervention.)

The areas are Flame Tree Zone, Strawberry Stand and Putaputaweta Bank.

In this recent release from honeysuckle, surviving trees at the kikuyu margin include karo, puriri, kanuka, manuka, karamu, taupata, tarata, puahou and ti kouka. Behind them down the bank, released trees include mahoe, kohuhu, hangehange, nikau, mapou, porokaiwhiri (pigeonwood), kanono and a single kauri juvenile. Revegetation of the kikuyu margin is intended to buffer these.

The tanekaha/kanuka forest of which Gahnia Grove forms about 100m of the Eastern, ridge-top, margin has been surveyed from Gahnia Grove down to the Upper Forest path, from the boardwalk below the Flame Tree Zone, to the forest path's entry at the lower recreational grassed area referred to as the "Glade", "field" or "paddock".

This area was found to hold a diverse kauri ridge community vegetation, very weedy only at its margin at the lower end of the Top field, and from the boardwalk up to the roadside, but largely free of weeds within the forest, other than several mature radiata and black pine, a dense infestation of Bulbil Watsonia in the manuka canopy along the Glade margin, and abundant infestations of Aristea ecklonii, whose seedlings currently occur in thousands under canopy in light to moderate shade.

This area has now been hand-weeded and included in the Restoration Methodology Trial, creating a herbicide-free area from the Glenfield Rd margin down to the forest path, from the Glade to the boardwalk.

In addition to the widespread Aristea and Watsonia invasions near the outer margin, we found numerous scattered weed occurrences within this area of forest canopy, including seedlings of bangalow, phoenix, climbing asparagus, ivy, pampas, and exotic pine. A similar annual survey for these and other new invasions will be needed to head off significant future forest destruction which would not be manageable by current Council contracts.

A pigtail cordon has been placed from Gahnia Grove down to the end of the Top Field or Glade, and cut gorse has been used to help define the border from there down to the Top Forest Path.

Observations of Tanekaha Ridge are here.