Methodology Trial Report for Year Two

Contents


Gahnia Grove Methodology Trial Hours for 2019/20

The hours of site work for the year 2019/20 have been recorded separately for Gahnia Grove (the Glenfield Rd forest margin worked on from 20 May 2018), Tanekaha Ridge (the forest area downhill of Gahnia Grove, worked on from June 2019) and Rimu Ridge (the Glenfield Rd forest margin North of Gahnia Grove, worked on from August 2019).

This separation of hours enables a rough comparison of the hours needed in subsequent years to control and eventually eradicate the mass weed invasion of a defined area by this Trial methodology, particularly with regard to kikuyu, honeysuckle, ginger, and tree/shrub weeds. The initially weed-dominated roadside forest margin site adopted in June 2018 for this Methodology Trial, and mapped in iNaturalist as a "Place", is called Gahnia Grove. It's Sitework hours serve as a measure of the time required to survey, monitor and restore by this Methodology...including a large proportion of time spent onsite observing, reviewing techniques, thinking and planning.

Gahnia Grove in Year Two received less than half the number of hours of sitework recorded in Year One. (The Year One totals, details of techniques trialled for specific weed species, and some side-by-side before/after views for Year One, are recorded in our End of Year One report.)

The combined area of the Trial in Year Two - ie Gahnia Grove, Tanekaha Ridge and Rimu Ridge - is much larger than Gahnia Grove itself, approximately one hectare.

Year Two hours

Gahnia Grove sitework 142
Rimu Ridge sitework 94.5
Tanekaha Ridge sitework 59
Total Trial site work 295.75 (excluding 33 hours by Trainee, solely in Rimu Ridge)
Teaching 10
Liaison 99.25
Community Liaison (passersby, Reserve users) 4
Monitoring & research (onsite, online, phone, email) 563
Total hours spent in 2019/20 on the Gahnia Grove Methodology Trial 973

The time-totals for monitoring, research, liaison etc are not compared year on year, as the Year Two hours in these categories were for the entire area of the Gahnia Grove Umbrella Project area, including Rimu Ridge and Tanekaha Ridge.

Volunteer Training
In Spring 2019 a Reserve user became a Trainee assisting the Trial, adopting his own area for supervised sitework on Rimu Ridge, where (excluding training time) he contributed 33 hours of site work over the remainder of Year One.


Gahnia Grove sitework - 142 hours

As expected, in Year Two of this Trial site work in the 2018 site was much less than in Year One; less than half the 2018/19 total of 328 hours, and averaging less than 3 hours a week. As in Year One, much of this time was spent in ecological survey, observation, planning, and trialling and assessment of additional strategies and techniques, moisture retention, fire hazard prevention and drought mitigation, rather than direct weed control. All functions being performed during the same site visits, it is impossible to determine the exact time spent on weed control, or how it could be achieved without the simultaneous asessment and planning, but we continue to find the efficiency of weed reduction to be improved by reducing and delaying intervention based on confidence in our assessment of growth rates, the regularity of ongoing survey and the success of minimal and specific intervention as needed. Very large and damaging occurrences of woody weeds and vine, both in the forest and on the sunlit margin, have become effectively inert, requiring only a minute or two to control regrowth 2-3 times a year, and from observations to date we expect all of these to be easily uprootable (vines) or dead (shrub/tree weeds) within another year or two.

Climate change-induced drought, possibly long-term, was an unexpected additional factor from January 2019, forcing urgent reprioritisation and the extended retention of more aggressive exotics eg Verbena spp, for their drought-tolerance, and the short-term retention of regrowth on weed trees and shrubs (privets, Arum, CHF, ginger) for their ground-cooling cover. Gahnia Grove is near the peak of the West-facing side of the ridge, exposed to the North and East by the absence of trees, in summer several degrees hotter than the same kikuyu margin 50-100m down the road, and up to 10 degrees hotter than a typical residential property 500m away.

Several thousand photo observations await selection for upload to graphically document the changes in plant communities so far through the implementation of the methodology and the effects of drought. There are already many examples among the Observations currently uploaded for each sub-site. Scrolling through each sub-site's observations ordered by date of observation gives an overview of the changing character of each area over the last two years. We hope to be able to provide more side-by-side photos in due course.


Kikuyu eradication and mown turf margin management

Kikuyu control was rapid and easily extended and maintained in the Annexe and Apron margins, where healthy trees to 4mH existed in June 2018. The areas pictured below are Arena and Cape Honey Flower Bank margins, where revegetation is challenging on an exposed dry ridge after mass removal of Cape Honey Flower (CHF), honeysuckle and blackberry, with very few viable trees among those released and a lot of bare ground to fill. The aim is a succession of wild revegetation, gradually evolving from exotic to native with ongoing selective weeding. The challenge is to anticipate the possible native seedlings in any area and maintain or provide habitat to meet their needs, while producing and maintaining ground cover and the tallest possible shade by whatever vegetation is likely at that time. Long-range weather forecasts, rates of growth of each species of native or exotic plant, and the ease with which arising exotic vegetation can be later controlled, are therefore of vital importance.

In winter there is little evidence of its aridity.
The "Arena" bank top in June 2018
Behind the barrier of bamboo poles and recently cut honeysuckle is mown kikuyu, extending beyond this image 25m to the left and 15m to the right, dividing the forest canopy from an outer row of trees to c. 4mH and several large stands of harakeke. Both forest margin and the outer row of trees were released from honeysuckle in June-August 2018.
The mown swathe was 5-6m wide from the hoheria, just right of centre in the image above, to the barrier.

The same view in July 2020

The hoheria has grown about 1m taller. All kikuyu is eradicated within the site, and the boundary has been extended outward to include the two harakeke, since kikuyu control around harakeke is difficult and perpetual


Cape Honey Flower (CHF) Bank kikuyu margin, looking South-West

in May 2018, mown and herbicide-edged


and in June 2018, with mowing edge moved back at our request


In January 2019 a band of woodchip mulch was added, to visually define the Trial site for contractors and Reserve users, and for aesthetics; it covered a mixture of coarse loose plant materials that would otherwise have provided a range of microshade and shelter, ie excellent seedling habitat, in the previously sprayed kikuyu margin.
These woodchips were very raw, did not begin to rot for two years due to drought, sun and soil moisture deficit, and suppressed most vegetation for at least a year. This mulch was removed selectively, in places and conditions conducive to plant growth, once the coarser material beneath was either rotted or could be used in less visible areas as ground cover.

In June 2020, a mixture of native and exotic herbs have replaced all the mown kikuyu as well as previously uncontrolled kikuyu down the banks. The mown swathe has retreated 2-3 metres, leaving two previously isolated harakeke connected to the surrounding revegetation and, like others in the forest margin, likely to be shaded out if canopy develops successfully.


The karamu holding up the honeysuckle in the foreground of the 2018 image is absent, having died in the year after release.


CHF Bank Top viewed from the South


in October 2018 with cut honeysuckle piled along the mown kikuyu margin, and in foreground at left, the two karamu that died,

|
this one leafing after release from honeysuckle, but later dying. Cape Honey Flower beyond is pre-intervention


in May 2019 , with the Cape Honey Flower (CHF) cut down. The dense mass of CHF flowering stems was found to be arising from only a few plants, with branches up to 4 m L extending over the whole 10m x 10m steep bank, suppressing the few old karamu and juvenile mapou
June 2019

and in June 2020


Looking South

|in June 2019, with one of the two dead karamu, and a survivor behind to the right lower down the bank growing vigorously

Oct 2019

and June 2020


Arena margin


Looking North in April 2019


and in Jul 2020


Our summary of kikuyu management for Year One was made here. In November 2019 we followed it up with this comment.

While we expected to battle the ongoing incursion of kikuyu into the restoration site, in fact it has required little effort. Some hours were spent experimenting with different ways to control it while presenting a tidy appearance at the mown edge, but until June 2020 it has been too short to do much with, and in fact faster growth would have been helpful.

At last it has reached, in some places, a length of about 50-100cm past the cordon. The lightly-rooted superficial runners were easily detached and folded back, preventing the further incursion of most stolons, as well as providing, in the shape of a wave-curl on the beach, a little shade-tent for seedlings of native and benign exotic herbs.

This was easily maintainable, and while not attractive, could be managed uniformly enough to give a pleasing sense of order .

However, this managed border received an unplanned cosmetic adjustment when we received 5m of wood chip mulch, for the improvement of moisture retention to protect wild seedlings and planned plantings of native vines and grasses. Unexpectedly, the mulch needed to be moved immediately, as motorists were arriving on the first subsequent weekend with bags and shovels thinking the mulch was free, so we moved it as quickly as possible to the cordoned site. That meant placing a lot of it directly on this wave-curl of live, pulled-back kikuyu, where it was not really wanted as the raw mulch spread in January 2019 has only recently rotted sufficiently to support either exotic or native seedling germination and development.

It is expected that in a few weeks this narrow band of mulch will be easily moved, along with rotting kikuyu under it, to areas that will benefit from it, eg under mature trees, and areas so bare, compacted and/or nutrient-impoverished that they have not yet produced much wild growth of any sort.

This unplanned addition of mulch in winter will have hastened the rotting of the "wave curl", making it appear tidier, for now, but the earlier process will then resume, letting the kikuyu grow, folding it back on itself, and arranging it as uniformly as possible.

The mown area has been reduced by up to 5m, the widest previously-mown swathe now holding native and exotic herbs and a few native tree seedlings:

June 2018
June 2020

June 2018
June 2020


Weed control

Beyond the eradication of kikuyu and its ongoing control on the outer margin, it is impossible in our Methodology to separate hours spent purely on weed-control, but we can report that very few hours were spent in Year Two on control of kikuyu or any other weed species in Gahnia Grove, ie the areas of mass weed control in Year One.

Year One had included a significant amount of time in actual weed control only from June-December 2018. Thereafter, the very little weeding was usually done, long before it became a threat to existing or potential native vegetation, as encountered during ongoing survey and monitoring of growth and new seedlings in the treeless areas, and explorations deeper into the forest.

Occasional new seedling invasions including moth plant, cherry, climbing asparagus, ginger, wattle, Castor oil plant, swan plant, ivy, and privets were uprooted.

Chinese and tree privet regrowth was occasionally suppressed on the 7 specimens suppressed initially in Winter 2018 by partial breakdown and ringbarking.
A tree privet 3mH in June 2018 after a one-minute manual intervention to prevent further suppression of young mapou, karamu and totara in the Annexe kikuyu margin(Observation here)
in November 2018(Observation here)
and in August 2019 (Observation here)
In 2020 it is completely dead, observation awaiting upload.

The technique was used with less frequent intervention and equal success from December 2019 on Rimu Ridge, on a tree privet c.2mH found under kanuka and karamu covered in honeysuckle. It grew vigorously on release to light, but after the initial suppression its regrowth was limited by the stress to the root system of maintaining the unproductive branches.

when re-observed in February 2020.


Scattered weed occurrences discovered on venturing further into the forest - eg cherry, Elaeagnus, ginger, Syzygium, Euonymus, Fatsia, Aristea, Agapanthus, Pinus juveniles - were, and continue to be, dealt with by brief interventions as encountered during exploration and monitoring. None are currently uncontrolled, ie capable of significant growth or reproduction before the next planned survey of that area.

No standing pampas remain in the forest of the Gahnia Grove Trial umbrella area, and only a few suppressed clumps remain rooted. Similar small clumps have been completely uprooted, and many used to suppress Aristea or Watsonia nearby, on the 2nd or 3rd visit. The large pampas stand within the manuka/rawirinui canopy below the Apron was completely uprooted by the end of Year One.

Pampas in the manuka/rawirinui canopy immediately below the Apron, in June 2018

The very large 6mH clump in the Annexe at the mown grass margin

lived its later life as an ongoing source of mulch to suppress previously-mown grasses
and has been allowed to grow each summer
for the slight low ground cover of its new leaves
but has been reduced to about a dozen live shoots, looped and knotted then folded onto

a decaying base now about 30cmH.


Some hours were spent, in a number of sessions, suppressing the dense and widespread invasions of Aristea ecklonii and Bulbil Watsonia throughout the forest area of Gahnia Grove, ie Forest below the Annexe, Forest below the Apron, Forest below the Arena, Forest below CHF Bank and Forest below Flame Tree Bank. While Aristea and Watsonia may be eventually suppressed by deep shade, there are many light breaks in the forest, and both weeds occupy areas of ground almost totally, with tightly wedged Watsonia bulbs and thousands of Aristea seedlings allowing no space for seedlings.

In the previously weed-dominated sun-exposed outer margin, occasional Blackberry and honeysuckle regrowth and missed roots were encountered throughout the year, but took surprisingly little time to control, especially where they had been covered with plant material, which, combined with the loss of most foliage, had weakened their roots.

The occasional weed seedlings and regrowth were addressed briefly and easily during periodic survey and monitoring, with only previously unaddressed weed invasions requiring a total of perhaps a dozen hours over the year; ie Aristea ecklonii and Bulbil Watsonia in the manuka canopy, and Elaeagnus, Kahili ginger, Euonymus japonica and Syzigium (paniculatum and/or smithii) in the wetter forest below Flame Tree Bank, adjacent to Rimu Ridge where we began initial survey, and spent most of our site hours, in Year Two of the Trial.


Moisture retention

Following the severe summer/autumn drought of 2019, throughout the whole of Year Two weeding was constrained in all areas of the Trial site, to avoid loss of shade and ground cover, to the extent of leaving live remnants of honeysuckle and bindweed in Rimu Ridge to restore green cover to the newly exposed ground.

Most of the site work hours since August 2018 have thus been spent on reducing fire hazard, maximising moisture retention, and trialling various strategies of species selection and rate of removal of the benign herbs, aiming to facilitate all possible native seed germination while achieving the maximum possible low shade and soil moisture retention.
This constraint continues, with June providing perhaps our only opportunity to reduce weed, (depending on winter rainfall).

Having struggled to create micro-shade wherever possible through the heat of 2019's summer, the winter of 2020 is being spent in any possible preparation for possible drought this summer, by

1. creating shade with any suitable material onsite, eg dead branches and brush

recently cut kanuka brush from a tree felling, stuck in the ground; as shelter and shade for potential seedlings, and initial climbing support for a planned planting of rauparaha (Calystegia sepium roseata, "Pink bindweed") and small Ipomoea cairica cuttings

and cut harakeke leaves

mini-shade tents for potential and existing seedlings

2. improving soil permeability and water retention by ground cover with live benign vegetation and the addition of mulch as available

appropriate to the needs of both existing plants and likely seedlings (native or benign exotic according to each area's progress), based on observations during the drought

3. planting drought-resistant native ground covers
Microlaena stipoides planted close to manually controlled kikuyu margin

and fast-growing vines, as tiny barely-rooted cuttings
Ipomoea cairica cutting taken the same day from the off-site parent plant and planted here, experimentally, for the comparative sun and warmth of this ridgetop, in the shelter of Esler's "Hairy legs" groundsel (Senecio eslerii), shrubby toatoa (Haloragis erecta), plantains and other exotic herbs

protected by mini-shade tents.

4. minimal disturbance of low shade and ground cover in the release of native seedlings

Two karamu seedlings under a karamu, released from Verbena incompta and other aggressive herb weeds, with partial shade and shelter maintained by sticks (Cape honey flower stems cut up) and small pieces of brush

by working around, rather than culling, drought-resistant exotic herbs eg Verbena incompta and V. litoralis, plantains (Plantago lanceolata and P. major), docks (Rumex species), even retaining, in some situations, some of the aggressively mat-forming Creeping buttercup (Ranunculus repens), which is suppressed with heavy mulch once less aggressive ground covers arise nearby.

<img src="https://static.inaturalist.org/photos/81881119/original.jpeg" width="400px"

Following the severe summer/autumn drought of 2019, throughout the whole of Year Two weeding was constrained to avoid loss of shade and ground cover, to the extent of allowing live remnants of honeysuckle and bindweed in Rimu Ridge to grow to restore green cover to the newly exposed ground.


Extension of wild native vegetation into the wide treeless areas of Gahnia Grove

Selective handweeding since June 2018 of this bank of mown kikuyu has resulted in about 50% native herbs and seedlings, and 50% benign exotic herbs. If this vegetation achieves sufficient height and density by summer to support more native seedlings through the dry season, the selective weeding strategy will be adjusted to reduce more of the exotics. Ti kouka and karamu seedlings seem to do well under 1m H single-stemmed annual herbs. Manuka and kanuka may benefit from more light, but to date the only surviving manuka seedlings, despite casting closed capsules on pieces of dead or pruned live manuka brush, have been under the low but dense shade of a leafy manuka branch growing horizontally at ground level.

To mitigate the loss of the canopy and ground cover of extensive dense honeysuckle, blackberry, kikuyu and other weeds, the tallest and densest growth possible of benign exotics continues to be encouraged, by every possible means. Those herbs observed to serve the purpose most successfully during drought are favoured over mat-forming, short-lived or drought-sensitive herbs and grasses. We continually monitor and release native herbs and tree seedlings "just in time", leaving them with close dense ground cover and just enough light for their needs. The light is very intense in summer, and even a 2 hour window of exposure through gaps in shade can cause stress. Since June 2020 we have exposed the larger karamu seedlings, since the warmth of the ridgetop location permits growth throgh winter, but expect to have to improvise shade in summer from harakeke leaves etc, for those not reached by that time by the slowly growing shade of the canopy margin and scattered surviving trees released from honeysuckle in 2018.

In Year One, during the summer/autumn drought of 2019 dense tall annuals provided excellent cover, sheltering the few native seedlings that did arise, but during the drought most herbs became dry and died or were cut down as to reduce fire hazard. Nightshades, Verbena incompta and V. litoralis were the longest and strongest survivors, and by Autumn there was almost a monoculture of Verbena.

The two species of Verbena present are so arid-tolerant, with stout, divaricating roots holding immovably to the clay soil even when wet, and their seedlings are so prolific and densely ground-covering, that they had become very dominant by the end of the first summer. Assuming the drought was over, and with hopes of less aggressive exotic herbs to nurse the germination of native seedlings, we suppressed most of the Verbena plants before the Spring of Year Two, expecting a repeat of dense ox tongues, wild carrot and their accompanying soft, low and scrambling herbs.

Unfortunately the drought resumed and intensified, the more benign herbs expired early in summer, and even the Verbena were unable to to repeat their performance as the soil moisture deficit worsened. In the treeless expanses of Apron, Arena, and CHF Bank Top, shade was not as dense through the summer and autumn of 2020, and by the end of the drought there was hardly a green leaf to be seen among the standing remnants of dried herbs.

Once again, however, both species of Verbenas hung on, though in a depauperate state; as did Black nightshade and the native Dark nightshade. The dried remnants of oxtongue and wild carrot were trampled down to mulch the many native herb plants by now developing from cast and bird or wind-dispersed seed (Dark nightshade, Eslers groundsel, shrubby toatoa, nahui) and used especially to nurture the few surviving native tree seedlings, now a few centimetres high (mostly karamu and ti kouka).

A future post will provide more detail on the species, numbers and development of wild native seedlings observed within the site, especially those that arose in areas released from weeds during the Trial. In the meantime, some of the native seedlings observed within the 2018 Gahnia Grove site area can be viewed by sub-site using these links.

By June 2020 rain had moistened the surface of the ground once again, and exploration among both tall and low benign exotic herbs revealed the surprising survival of about 200 native tree seedlings, mostly karamu and ti kouka, many of them last seen as newly arisen seedlings in 2018 after the initial widespread weeding. Most had been barely visible, some completely hidden, under the herbs. Karamu and ti kouka 10-30cm H grew under nightshades and toatoa in or near the dripline of karamu, mapou, manuka and rawirinui. Two dozen karamu emerged to 10cm H from a tight close ground cover of plantains, buttercup, daisies and grass regrowth (and are each being given a centimetre more space as they need it).

Many of these had earlier been seen drought-stressed and were not expected to survive.

Under the first manuka to be released from honeysuckle, about a dozen ti kouka nursed by plantain, wild carrot and ox tongue now range from 20-80cm high.

Thousands of smaller seedlings have arisen in the dry leaf litter under small trees at the top of the Annexe, in space previously dominated by a 5mH pampas. A similar germination in 2019 succumbed to drought, and this year's crop have yet to demonstrate their ability to survive the coming summer. Weeds are not a problem here, the only competitors being drought-starved catsears (Hypochaeris radicata) and Herb robert (Geranium sp), but there is little humus or ground litter, so handfuls of decayed pampas or woodchip mulch are being scattered for moisture retention wherever there is space between the tree seedlings.

Most of the surviving seedlings occurred under surviving Coprosma or manuka released from honeysuckle. Tightly grouped, their numbers will drop as they continue to compete.

The introduction of native herbs Shrubby toatoa (Haloragis erecta), and Esler's groundsel (Senectio eslerii), along with the spontaneous occurrence of the native Dark nightshade (Solanum opacum), have resulted in a few dozen native plants of 1-1.5mH effectively hedging small areas, albeit not densely enough to protect many seedlings through the last two drought summers.

These mature native herbs have now resulted in hundreds of their own seedlings, which we favour over their exotic counterparts as we continue selective weeding in hopes of an assisted wild transition from weed wasteland to native forest margin.

Whether, or how soon, this is achieved is dependent on the weather and climate change that has, since January 2019, so severely impacted this area, and particularly this hot, exposed and treeless area of roadside ridge-top.


The outcome for the most seriously-affected trees released from honeysuckle in 2018

Several of the five karamu, and a juvenile akeake, all estimated to be 10-15 years old but, due to the dense weed infestation, standing in isolation almost completely covered by honeysuckle, were found on release to be almost leafless, with 30-90% of major branches dead.

Two of these karamu and the akeake recovered briefly, flowered and fruited, then died during the 2019 or 2020 summer/autumn droughts.

Despite the extreme drought-stress suffered by all the vegetation on the ridge, particularly evident since March 2020, the other three karamu released from honeysuckle in 2018 have grown 2m taller densely leafy over the two years since release, and now provide pockets of low shade, as well as fruit and seeds.


Three juvenile putaputaweta in the kanuka margin partially exposed by the June 2018 removal of honeysuckle were outside their expected comfort zone this far up the dry ridge. The largest, juvenile was almost completely canopied by undisturbed rawirinui, manuka and mapou, but with no replacement ground cover having emerged on adjacent uncanopied ground bared by kikuyu and honeysuckle removal. It died soon after the 2019 winter rains came at last.

The smaller two, more exposed but on the lower part of the bank, did well the first year.

They were behind a dead tree, which during the first year dropped its branches and then the top half of its trunk.

The lower 2m of the broken trunk remained upright and was used to support a shade tent formed from its dropped branches interwoven with its brush and cut harakeke leaves.

February 2020, upper half of shade tent visible above exotic herbs. The shade tent was added to over subsequent months as suitable material became available and the drought increased in severity

This reduced signs of drought stress in the putaputaweta from early summer in 19/2020, but, as with the first specimen, both these smaller putputaweta began to lose all their leaves shortly after the eventual onset of winter rain. The smaller of the two died, but the larger began to grow new leaves and, at 4 July 2020 was doing well.

Juvenile putaputaweta with regrowth after the recent death of all its leaves in first winter rains following drought drought (shade tent has been mostly dismantled)

Three severely diseased and deformed karamu near the top of CHF and Flame Tree banks were released in December 2018 from complete cover by dense, heavy mounds of honeysuckle, in an area where Tradescantia was subsequently removed. These three karamu initally leafed out, but lost many leaves in the 2020 drought. Two are now leafing out once again with winter rains. The third, the largest, further down the bank, was less involved in honeysuckle but the most damaged, (possibly near the end of its natural life) and may not recover.

Three tall ti kouka in the canopy margin have yellowed leaves and are stunted, as they were before intervention, possibly due to chronic soil moisture deficit.

In contrast, an unbranched 4mH ti kouka, leaning sharply on release from complete cover by honeysuckle to its neck, now has four erect basal shoots, each shoot 1-2mH, on the lower part of the leaning trunk, supported by sturdy new aerial roots. (This tree is rooted beside a shallow runoff channel).


Wildlife in Gahnia Grove

During the assisted wild transition from weed wasteland to native forest margin many invertebrates take advantage of an expanse of low herbiage and floral abundance in summer, including the Bombus terrestris small bumblebee,

honeybee

and Fungus eating ladybird, which thrive on the fungal bloom that overtakes the oxtongue after flowering

The only lizard we have seen, unfortunately, is the new-to-us but now locally common and invasive Plague lizard.

Twenty years ago in this Reserve network and neighbourhood we encountered only copper skinks, notably absent during this Trial.

Tui, thrush and blackbirds frequently descend to forage in recently weeded areas.
A particularly frequent and prompt attendee last summer was this flightless female with deformed wing and beak, whom we believe to have been inhabiting the undergrowth at ground level. She was seen once preening while standing vulnerable on the ground - not a behaviour I have seen in flying birds.
Visits ended when there was no moisture to be found on site night or day. Water was probably not within walking distance for this disabled bird.


Planting

The planned planting for Gahnia Grove is to provide the fastest possible soil and moisture retention and shade by supplementing the wild revegetation of herbs (which become dry in summer drought) and native seedlings (which require at least low shade and shelter).

The 2020 planting consists of

  • two fast-growing native vine species believed appropriate to the area, to shade and shelter the canopy margin and new generation of plants:

rhizomes of Rauparaha "Pink bindweed" (Calystegia sepium subsp roseata)
collected from the extensive occurrence covering almost all of the raingarden wetland planting on the Domain Rd margin of Eskdale Forest

and recently-rooted cuttings of "Coastal Morning Glory" (Ipomoea cairica) taken from a single plant

This plant was cultivated during 2019 from a small cutting collected from a single wild specimen observed in 2018 in the Domain Rd canopy margin of Eskdale Forest before it was overtaken by Arundo donax and other weeds. (Observations here)

These plantings are experimental and may limit or overcome other native seedlings and juveniles. However, the need for shade, shelter and reduced temperature is urgent and extreme. Unless there is a reversal of current climate changes, the benefits of having in 2018 released Gahnia Grove from honeysuckle, blackberry, ginger, Arum, Calystegia silvatica, Agapanthus, privet etc may have been outweighed by the loss of their shade, shelter and ground-cooling greenery, other than having halted the rampant spread of honeysuckle through the forest.

  • isolated small specimens of native grass Microlaena stipoides throughout the exposed reas of the site, hoping they will establish, multiply and in due course provide ground cover between trees, as this species is observed to do in wild forest margins nearby where herbicides have not been used.
  • a few wrenched or potted wild local seedlings 6-10cm H: karamu, kawakawa, mahoe, Carex dissita/lambertiana/flagellifera
  • small uprooted pieces of native ground-covers collected from home nearby, where they have occurred wild and over the years formed dense mats, filling bare patches of lawn and cracks in paving, and can be walked on. These are Basket grass (Oplismenus hirtellus subsp imbecilis), Nahui (Alternanthera nahui), the tiny Carex inversa, and creeping Hairy pennywort (Hydrocotyle moschata), all of which have arisen wild in our nearby home garden, and have also been observed locally among wild native regeneration.

Lobelia anceps (Shore lobelia) also occurs in our home lawn and garden borders, and self-seeds persistently under kanuka, among Carex and in potted plants, but has not yet been successfully transplanted to Gahnia Grove. Like Microlaena stipoides, Lobelia anceps is present wild at several locations in Gahnia Grove's manuka canopy, and may increase with rainfall if it remains undisturbed.


Rimu Ridge (sitework - 94.5 hours)

El Sitio Top in November 2019

Like most of the trees in about 50 x 20 m of planted forest margin bordering mown kikuyu, these ti kouka , pohutukawa, karo, karamu and mahoe are almost completely covered in, and their trunks and branches being strangled by, the Japanese honeysuckle infestation present in varying densities through the planted forest margin from the cemetery North towards Domain Rd.

This infestation extends at least 50 m into the diverse streamside and kauri forest communities on the ridge below. It is seen climbing to at least 10m high, and we are interested to discover the limits of its ability to invade and topple tall forest trees.

The planted margin and forest within the boundaries of this Trial are now almost free of obviously infestation but will need ongoing manual control of regrowth, and remain vulnerable to invasion through the canopy to the North, below the petrol station.

and in July 2020
almost the same view, (at the head of the ephemeral stream) after release from honeysuckle

Of great interest at time of writing is the ephemeral stream El Riachuelo, dividing Pohutuwawa Bank frrom El Sitio as it descends the ridge through a stream-fed community of putaputaweta, nikau, porokaiwhiri (pigeonwood) and hangehange.

Rimu Ridge also provides additional data on control of honeysuckle, ginger, kikuyu and palmgrass by a refinement of the methods of gradual reduction and self-suppression we had found effective in Gahnia Grove, consuming less time and effort while retaining more ground cover.

The further exploration of Gahnia Grove's Northern boundary was driven by the need to address the oncoming honeysuckle from the forest/roadside margin to the North. In August 2019 this area was adopted into the Methodology Trial as an extension to Gahnia Grove, naming it Rimu Ridge because of a magnificent rimu just above the forest path below, at the foot of a steep bank primarily occupied by a few radiata pine, wattles and a wide variety of invasive weeds, with several c. 10m H planted pohutukawa at the top.

The short time available for urgently-needed control of honeysuckle to prevent more tree deaths throughout the 50m length of planted forest margin resulted in a much less thorough removal of vine that we had done in Gahnia Grove, leaving vines rooted throughout the many stands of harakeke, at the bases of trees, and much of the ground in between. The need to suspend further weeding in December 2019 to prevent loss of ground cover and dessication limited the work further.

Fortunately Strawberry Bank, one quarter of Rimu Ridge, held dense Tradescantia mixed with uncontrolled kikuyu. This heavy wet mass was gathered upward, together with the unrooted sections of honeysuckle vines, and left in a widespread ground-covering mass over Spring and Summer. As expected, a subsequent visit found the honeysuckle's fine roots had weakened sufficiently to uproot much of the remaining vine. The remaining mixed kikuyu and Tradescantia were then left undisturbed. The bank remained wet and the trees on it fared well in the ensuing prolonged drought. In June 2020 there was only a small amount of honeysuckle, discovered only by uplifting Tradescantia and easily uprooted.

The dry ground in, under and around the many harakeke still holds honeysuckle, perhaps 1% of the amount initially present and growing rapidly pre-intervention in June 2019.

The areas without Tradescantia were more heavily infested - in fact almost completely covered, climbing trees to c. 12 m H and with trees up to 6 m H unidentifiable under its dense cover. Many of the trees released (mahoe, karo, ti kouka, pohutukawa, manuka, rawirinui, karamu, taupata, akeake, puriri, hangehange, nikau, porokaiwhiri/pigeonwood, putaputaweta) were found deformed and almost leafless, but most immediately started to leaf out, and in fact their lack of leaves may have helped them survive the ensuing drought, and their abundant development of foliage since may hinder their survival of hot dry periods this summer. If so, for weed-covered trees with severe leaf loss we will reconsider our assessment of the best time to remove mass vine weed from severely affected trees, which to date has been, as for less-affected trees, to release them well before drought begins, to allow acclimatisation to the increased shade and loss of ground cover before the heat and drought of summer.

From January 2020, with severe soil moisture deficit prohibiting both ground disturbance and any loss of shade, the focus returned to moisture retention and the rearranging of cut or dead vegetation for maximum possible shade. This need intensified with the ongoing drought, especially in recently-released areas, where replacement ground cover by introduced herbs and grasses was very slow to develop due to drought, and cut weed rapidly dried, requiring removal from the exposed margins alongside the recreational roadside grass into the shade of canopy behind, for fire safety.

All that could be done until June 2020 was to create shade where possible for recently-released mahoe suffering from drought stress, using bamboo, fallen branches and cut vine. These appeared to give relief for the remainder of the drought, and all the trees except a few karamu found already moribund under the honeysuckle, are now leafing fairly vigorously. Some of the most severely affected mahoe may die later.

Rimu Ridge's ephemeral stream, "El Riachuelo"

In June 2020 the return of winter rain combined with the first reduction of a dense palmgrass infestion in El Sitio revealed the enchanting sight of clear running water, evidently an ephemeral stream, emerging from a hidden opening beneath stable ground on El Sitio Top, and dispersing into the forest below El Sitio, where it may contribute to the steep forest stream suggested by the deep irregular channel that divides El Sitio from Putaputaweta Bank.

This deep, steep channel ends at a long series of boardwalks over the forest path below, where a deep channel appears to be the confluence of at least two underground streams as well as overground run off from Gahnia Grove's Flame Tree Bank and Cape Honey Flower Bank.

This channel dividing Putaputaweta and El Sitio Banks, as seen from the boardwalk below, almost exactly reflects, in topography and plant species and density, the photograph used to illustrate an educational publication produced for Auckland Council about the importance of steep forest and ephemeral streams, so we have linked that article in our post about El Riachuelo.

The discovery of El Riachuelo has thus provided the beginnings of an answer, which we hope will be followed up with water quality and habitat assessment, to our longstanding curiosity sparked by the googleearth satellite view and history suggesting two streams and their confluence at the boardwalk below Towai Bank, below CHF and Flame Tree Banks. It also corresponds to the streamside plant community, in places vestigial or embryonic, extending from Cape Honey Flower Bank to El Sitio Bank.

The corresponding change in vegetation is seen from the forest path between a boggy and deeply rutted track with a drain at the base of a kauri ricker, and the large old rimu above the path shortly before it turns down to follow this branch of Kaipatiki Stream down to the Harakeke plantation and thence to Hiwihau Reserve. The steep narrow channel ends in a pool clad densely in lush streamside ferns, trees and vines, its overflow running beneath the boardwalk of the forest path.


piupiu (gully fern), kiokio, panako (thread fern), puhinui (Adiantum cunninghamii) kanono, towai, hangehange, mingimingi, tataramoa (Rubus cissoides), Carex and mosses, karamu, mahoe and ponga - all visible in this photo of less than one metre of pathside bank (along with invasive African club moss and Elaeagnus). This waterfall pool, visible beside the public forest path at the boardwalk, is directly below El Sitio, and presumably the downhill end of El Riachuelo.

A few metres below, an unstable and irregular channel several metres deep appears to hold the confluence of El Riachuelo and an ephemeral overland flow down the Flame Tree and CHF banks of Gahnia Grove, together a tributary of the Kaipatiki Stream's Eastern arm through Eskdale Forest to its significant estuary in Beachhaven on the Upper Waitemata Harbour.

The bank above this pool below El Sitio is not within the boundaries of the Gahnia Grove Trial, though its beauty and diversity - where not overrun by Elaeagnus, ginger, Syzygium and honeysuckle - are a model for our restoration of similar terrain above and on adjacent banks.


Tanekaha Ridge (sitework - 59 hours)

Exploration of the Western boundary of Gahnia Grove, as far downhill as the forest path across the ridge, revealed a fascinating regenerating dry kauri ridge community, currently dominated by rawirinui and mapou, a group of nine young adult Maritime pine with scattered juveniles including two growing rapidly alongside the sole kauri ricker, and scattered young tanekaha and other podocarps, and radiata pine. The understorey is almost entirely native, of shining karamu, akepiro, mingimingi, hangehange, screw fern, spleenworts, Waewae kotuku (Gleichenia microplyllum and dicarpa), bushy clubmoss, Dianella nigra and rushes, particularly kauri sedge.

Tanekaha are abundant at all stages from seedlings to young adults. There are isolated young adult kauri (probably less than 60 years old with a few juveniles and seedlings, rewarewa, kahikatea, miro, rimu, with mature kohuhu, toru, Dracophyllum sinclairii, and Pseudopanax - horoeka, puahou and houpara.

Even the outer margin canopied entirely by rawirinui and the nine Maritime pines holds a strange charm, with its deep pine litter nursing thousands of future native forest trees, and dense stands of kauri sedge (Schoenus tendo) and Gahnia xanthpocarpa in an open understorey of kauri-associated trees, shrubs and ferns.

The deep cushions of native mosses are a delight to behold

and the beauty of the seminal kauri ridge community was broken only, but jarringly, by occasional scattered invasives (Phoenix, Chusan, Bangalow, fan palm, Agapanthus, Bulbil Watsonia, Aristea Ecklonii, seedlings of ivy, climbing asparagus and honeysuckle, young pampas, Japanese cherry).

Longing for the privilege of ongoing access to this lovely area, and believing the weed invasions observed in Tanekaha Ridge to be manageable with 1-4 annual visits to each area, we adopted this Western extension to Gahnia Grove also, naming it Tanekaha Ridge. We are committed to arresting the development of the new weed invasions, and eradicating those species which have become established, with the exception of the mature and larger seedling pines and cherry trees, the removal of which would require arborism. (By far the majority of those weed observations are within the very weedy section of margin we call Cherry Bay, and its adjacent canopy in Puahou Corner).

We limit these foot tours to prevent disturbance, soil compaction and root damage, addressing all weeds present in any area while there, and visiting it thereafter through our photo files, which also help to obtain identification of those species new to us.Tanekaha Ridge evaluates the spontaneous regeneration of an area of rawirinui/podocarp forest on a dry kauri ridge, the numbers of new weed invasions occurring annually through seedlings, and the potential to keep an area of established forest weed-free by ongoing monitoring and manual control.

After the adoption of Tanekaha Ridge from August 2019, "Cherry Bay", a very weedy stretch of forest/recreational grass margin around a cherry tree, required an initial investment of many hours to control pampas, mothplant, honeysuckle, wattle, woolly nightshade, climbing asparagus, Arum, ginger, ivy, tree privet and Carex divulsa, with juvenile wild cherry trees, seedling bangalow and phoenix palm in the adjacent forest canopy.

The ongoing suppression of Aristea ecklonii and Watsonia throughout the dense manuka canopy below Gahnia Grove was extended down the ridge to include Tanekaha Ridge's manuka margin.


The annual emergence of new leaves of Bulbil Watsonia typical throughout the c. 100 x 10m of manuka canopy margin

Posted by kaipatiki_naturewatch kaipatiki_naturewatch, June 30, 2020 21:27

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