Gahnia Grove - Umbrella Project's Journal

Fortunately, it appears that the recent Indian Dipole effect that contributed to Australian and NZ drought in the last few years is ending, or ended:
https://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=12299203
These Dipole events have not apparently been recognised and recorded over a long history, but are reported to have occurred with increased frequency in the last decade or two, and are predicted to occur more frequently with global warming.

Though the recent Diplole event may have concluded, the Auckland drought persists and "The New Zealand Drought Index (NZDI) shows that meteorological drought and severe meteorological drought remain in place across parts of the Coromandel Peninsula and a small part of northern Auckland."

https://niwa.co.nz/news/hotspot-watch-1-may-2020

Confirmation of our observations in Gahnia Grove, where the impact of the drought is visible and tangible, particularly because of itstreeless, roadside ridge-top situation. Temperatures recorded by our camera on the ridge and specifically at the treeless bank top of Gahnia Grove's Arena and CHF banks, have confirmed our formerly untested pperception that this ridge is several degrees than streets a few hundred metres away, and the kikuyu at the top of Gahnia Grove is several degrees hotter hotter than Rimu Ridge, ie 50-100m down the road on the same Northern aspect of this East/West facing ridge.

The light intensity and angle change throughout the day, so that leaf litter under trees in a cool shady spot at 10am can be hot to the touch at 2 or 3pm.

None of this is surprising, but land managers need to be aware of the conditions being experienced in this location, to take into account the extreme stress currently experienced by vegetation, and likely unprecedented impacts of works impacting soil and plant hydration, eg the planned removal of the large stand of Flame Trees, the source of a growing invasion down the adjoining forest, but also the most significant source of shade along this ridge in summer, at a gullyhead with a streamside plant community.

Some of the native seedlings observed within the boundaries of Tanekaha Ridge , ie the forest between Gahnia Grove and the forest path, from the margins of the mown recreational grass field to the gully below the Flame Trees,
and from there North, on Rimu Ridge. The majority of observations made on Rimu Ridge have yet to be uploaded.

People visiting the Eskdale Forest's Glenfield Rd margin often stop, comment on or ask about the restoration project, and some express an interest in casual participation.

We encourage them to contact the Kaipatiki Project and the Auckland Council Community Ranger for training and co-ordination, as we do not have any free time to offer to train and supervise them, and until now none have indicated they already have the necessary plant identification skills, ecological awareness and commitment to training.

Happily, in November 2019 we accepted an ideal trainee and volunteer into the Methodology trial, allocating them a discrete area of operation. The creation of El Sitio and Pohutukawa Bank extended our Northern boundary by about 50m and forms a large part of Rimu Ridge.

While this has of course involved some extra input of time on our part, it has been rewarding to find that the fundamental principles of this methodology are transferable to those with corresponding aims, skills and aptitudes.

It has also resulted in a good deal of honeysuckle being controlled in a previously unaddressed area.

Working North along this margin to control the imminent reinvasion of honeysuckle to Gahnia Grove from the North resulted in release, mostly from Japanese honeysuckle but also some moth plant and Elaeagnus, of a few dozen trees 4 -8mH. Many of the vine-covered trees were mature, fruiting wherever a branch tip could still penetrate the weed to reach sunlight,

This has produced an extension of the Gahnia Grove trial methodology along the Glenfield Road-side upper margin of Eskdale forest and created the new sub-sites "Strawberry Stand Bank, Putaputaweta Bank, El Sitio, Pohutukawa Bank", and the "Forest below ----" each of those.

This combined area of extension contains a markedly more diverse and streamside community with many Putaputaweta, as well as extensive dense mats of Blechnunm filiforme and Adiantum oblongifolium.

To identify the area for contractors and volunteers, the pigtail cordon along Gahnia Grove at Glenfield Rd has been extended North almost to the petrol station,

To maintain the validity of the data produced for Gahnia Grove from June 2018 -June 2019 Year 1, and for that c. 60 x 40m area, the hours of work and the observations for this extension are being tallied separately.

This June 2019 streamside-community extension North is being referred to as "Rimu Ridge". (cf the extension June 2019 into the kauri-community forest downhill to the forest path is referred to as "Tanekaha Ridge").

This lovely regenerating forest holds towai and other uncommon species, and is infested by Elaeagnus of up to 10cm D. trunks and thorns 8cm L, Japanese honeysuckle up to 6cm D in the margin and up to 2cm D 20 metres into the canopy among the ground ferns and in the trees, many square metres of a monoculture of Palmgrass/Palmaria setifolia, and occasional Madeira tubers, all of which are being contained, suppressed or uprooted as appropriate to this stage of the Project.

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.

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.

October 23, 2019

Culling the ox-tongues on Strawberry Bank - and mulching the first natives
Oxtongues are now dense in the Strawberry Stand Bank kikuyu margin, as along much of the previously sprayed Eskdale Forest Upper Margin North.

Growing as close as a few centimetres apart and up to about 1m H, their single stems are leafless to about 30cm H, providing ideal nursery conditions for light-loving native plants. Oxtongues were culled today to make spaces for natives, initially for quick-growing herbs such as Haloragis erecta, Dark nightshade and Esler's weed, and if necessary for some of th less aggressive exotic herbs which will be easy to remove when the natives arrive.

The ox-tongues are also being culled before they flower, to use as mulch while they are still leafy, as once they they flower the leaves shrivel.

As mulch, they help retain moisture in the ground (which is already very dry on the surface) , and create humus to support other seedlings.

During culling we found two Haloragis erecta (shrubby toatoa) seedlings and a Pteris tremula sporeling. Both were mulched heavily with cut ox-tongues to keep weeds from arising next to them and to feed them.

A number of observations have been made specific to the management of the kikuyu invasion of the forest and planting margins generally in Eskdale Reserve's Upper Forest margin, and documenting the management of these margins in Gahnia Grove.

For clarity and detailed ongoing monitoring, these have been divided into (in order of development over time - ie work on CHF Bank and Flame Tree Bank was only begun in November 2018) the mown kikuyu margins of:
The Arena
https://inaturalist.nz/projects/gahnia-grove-arena-kikuyu-margin
The Apron
https://inaturalist.nz/projects/gahnia-grove-apron-kikuyu-margin
The Annexe
https://inaturalist.nz/projects/gahnia-grove-the-annexe-kikuyu-margin
CHF Bank
https://inaturalist.nz/projects/gahnia-grove-chf-bank-kikuyu-margin
Flame Tree Bank
https://inaturalist.nz/projects/gahnia-grove-flame-tree-bank-kikuyu-margin

Also being hand-weeded, hopefully to be formally included in the area for suspension of edging services, is the Annexe canopy/Top Clearing margin of mixed exotic grasses incl. kikuyu:
https://inaturalist.nz/projects/gahnia-grove-annexe-canopy-clearing-margin

Explanation of the method specific to kikuyu control,with some observations from all the above areas of kikuyu margin, is at "Kikuyu Edge in Transition to Native Ground Cover"
https://inaturalist.nz/projects/gahnia-grove-kikuyu-edge-in-transition-to-native-ground-cover