Gahnia Grove - Site summary and discussion's Journal

June 30, 2020

Methodology Trial Report for Year Two

Gahnia Grove Methodology Trial Hours for 2019/20

The hours of site work for the year 19/20 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 area of Gahnia Grove serves as the measure of this assessment, having received in Year Two less than half the number of hours of sitework recorded in Year One. (The Year One totals are recorded in our End of Year One report.)

The combined area of the Trial in Year Two was 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 hrs (excluding 33 hours by Trainee, solely in Rimu Ridge)
Teaching - 10
Liaison - 99.25
Community Liaison (passersby, Reserve users) - 4
Monitoring & research - 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 the year.

Gahnia Grove sitework - 142 hours

As expected, site work in the 2018 site, in Year Two of this Trial was much less than for the 1st year, less than half the 2018/19 total of 328 hours. 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.

Several thousands photo observations await selection for upload to document all of these, but there are some examples among the Observations currently uploaded for each sub-site, and we hope to be able to provide a selection of side-by-side photos
in due course.

Kikuyu eradication and mown turf margin management

CHF kikuyu margin, looking South-West in May 2018, mown and herbicide-edged

In June 2020 the kikuyu margin has moved 2-3 metres back from the earlier margin. The karamu holding up the honeysuckle in the foreground of the 2018 image is absent, having died in the year after release. A mixture of native and exotic herbs have replaced all the mown kikuyu. No native tree regeneration here yet.

looking North in October 2018
(in the foreground is the same karamu, initially leafing after release from honeysuckle, but later dying )

and in May 2019

and South in October 2019

CHF kikuyu margin looking West
June 2018

November 2018
May 2019

Annexe grass margin looking North
September 2019

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 growth inwards 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 soil moisture, texture and fertility.

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.

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, very little weeding was needed, usually 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.

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 Annexe was completely uprooted by the end of Year One.

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.

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

- creating shade with kanuka brush, harakeke leaves and any other suitable material onsite

- 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

- planting drought-resistant native ground covers and fast-growing vines, as tiny barely-rooted cuttings protected by mini-shade tents

- releasing native seedlings with minimal disturbance of low shade and ground cover, 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 the aggressively mat-forming Creeping buttercup (Ranunculus repens).

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 leaving live remnants of honeysuckle and bindweed in Rimu Ridge to restore green cover to the newly exposed ground.

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

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 the 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).

Native tree seedlings

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 are now 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 and herb robert, but handfuls of decayed pampas 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 - Nahui (Alternanthera nahui), 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 my be achieved is dependent on the weather and climate change that has, since January 2019, so severely impacted this area, and particularly this hot, dry 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, 10-1 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 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.
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.

Three severely diseased and deformed karamu near the top of the bank, rooted where Tradescantia was gradually reduced by hand in what was planned as a staged eradication of Tradescantia from the site, initally leafed out but lost many leaves in the 2020 drought. Two are now leafing out gain, but the third, the largest, further down the bank and less involved in honysuckle and the oldest but the most damaged, (possibly near the end of its natural life) 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,

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 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.


Planned further planting of native vines on CHF Bank has been deferred due to flooding and erosion occurring following filling and compacting of the roadside apparently resulting in impermeable surface directing road runoff directly onto this bank, washing out some small plants and exposing the roots of many plants, including large trees. As soon as this is remediated through the restoration, and maybe increase, of widely disseminated vegetative filtration and absorption, planting of native vines on CHF Bank will be resumed.

The planned planting for Gahnia Grove is to provide the fastest possible soil and moisture retention and shade by supplementing the wild revegation 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 Domain Rd

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 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 multiply and provide ground cover

- 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), Carex inversa and 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 the home lawn and 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)

Rimu Ridge provides additional data on control of honeysuckle, ginger, kikuyu and palmgrass by the methods of gradual reduction and self-suppression we had found effective in Gahnia Grove,.

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 magnificent rimu just above the forest path below, at the foot of a steep bank primarily occupied by a radiata pine and a wide variety of invasive weeds, with planted pohutukawa at the top.

From December 2019 weeding was suspended throughout the Trial, not only in the treeless expanses of Gahnia Grove but even within the canopy, including Rimu Ridge where trees had been released from honeysuckle, but the ground still held a network of rooted runners.

In 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 intensifying 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 trees are now leafing fairly vigorously, but some severely affected mahoe may die later.

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 dotted with tanekaha and other podocarps, with an understorey of shining karamu, mingimingi, hangehange, kauri community ferns, clubmosses, Dianella nigra and rushes, particularly kauri sedge. Tanekaha are abundant at all stages from seedlings to young adults, and there are isolated young adult (probably less than 60 years old) kauri, rewarewa, kahikatea, miro, rimu, with mature kohuhu, toru, Dracophyllum sinclairii, and Pseudopanax - horoeka, puahou and houpara.

Even the outer margin canopied by hard pines holds a strange charm with its thousands of future native forest trees and dense stands of kauri sedge (Schoenus tendo) and Gahnia xanthpocarpa

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 minimal weed invasions observed 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 pines, and cherry trees, the removal of which would require Resource consent and arborism.

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.

Posted on June 30, 2020 21:27 by kaipatiki_naturewatch kaipatiki_naturewatch | 0 comments | Leave a comment

June 28, 2020

Flooding and erosion after filling and compacting of previously permeable roadside

The meeting with Stormwater engineers is scheduled for 10am Tuesday 7th July.

We were delighted to receive a call today from Healthy Waters (the new name for the Stormwater department of the Auckland Council), and be updated on current Council policies and procedures in relation to stormwater, suggesting solutions along the lines proposed below are likely to be considered. A site meeting with members of that team is expected tomorrow.

After a period of steady rain this morning we observed the area again, and the flow pattern seen yesterday was being additionally fed by a steady stream of water down along about 100m of roadside edge uphill, mostly channelled in the unfilled section of road edge adjacent a roughly grassed berm, which is slightly inundated, with water pooled in some deep ruts and holes made by vehicles in the grassed area last year.

Following this roadside stream as far as the bus stop opposite Speedy Crescent, where the kerbside is paved, we saw a gutter drain with no apparent movement of water into. We eventually reached Call Centre and asked them to advise Stormwater North, to whom the issue has been apparently escalated as we were advised yesterday would happen, of this additional observation.

Video of roadedge/berm flow, viewed from CHF Bank uphill to the bus stop and gutter drain opposite Speedy Cres

SUNDAY 28 June
Recent erosion, and damage to vegetation within the forest, has been seen only in the last few weeks, since recent first rains after drought and after filling and compacting of previously permeable roadside. Close observation throughout this roadside edge at least weekly since June 2018 has revealed no flooding or visible erosion by runoff during that period, although there is some channelling presumably due to run off patterns at earlier stages of road development. Eg We note that this section of road was raised and levelled during widening approximately 15-20 years ago.

New erosion channels have been formed in recent weeks, down the bank and through the forest below, washing away native seedlings, burying juvenile treeferns in piles of debris and topsoil up to 50cmH, and exposing roots of mature trees on the steep bank of the canopy margin, including kanuka 10mH, pigeonwood, ti kouka, mapou and treeferns to about 8mH.

Adjacent to this new run off channel down through the forest are several mature nikau, the only mature nikau in Gahnia Grove (with a few present on Rimu Ridge and Tanekaha Ridge).

The new runoff channel through the forest was observed when it was not raining, and no running water was seen. The recently dumped soil and debris ended some metres above the boardwalk of the forest path, presumably running underground or through deep debris from that point to the one-metre-wide, several-metre-deep chasm, or stream tributary, below the boardwalk.

Our first consideration was whether the eradication of shrub and vine weeds in June-December 2018, or of kikuyu, the eradication of which was extended a metre or so in this area during 2019, had contributed to increased runoff. However:

1. Though the water is more evident where there is no kikuyu, there is also current flooding of the mown kikuyu slightly uphill, particularly in a well-trodden line evident through the centre of the mown swathe since the summer drought when even the kikuyu became sparse.

2. There is no indication of increased runoff - or indeed any - in the adjacent areas of Arena and Apron, where kikuyu eradication was similarly extended.

3. The major removal of shrub and vine weeds was completed by January 2019, and there was no evidence of flooding or erosion after the heavy rains of April 2019 or thereafter.

We note also that the Gahnia Grove zones encompassing the twenty metres of roadside uphill of here, ie the Annexe, Arena and Apron, remain dry, the soil only superficially moist and crumbly, despite similar weed eradication (which is always accompanied in our Methodology by at least superficial replacement of ground cover and soil retention, immediately by plant material placed across the slope in such a way as to retain debris and slow run off, and as soon as possible thereafter by growing plants, eg exotic herbs to begin with).

The volume of water now seen running down the roadside surface, (presumably evident during heavy rain continuing down the steep bank and forest floor below), instead of reaching the mown grass adjoining these areas of slightly higher elevation than the flooded area, suggests those higher areas are currently missing out on much of the gentle widespread winter soil seepage observed in 2018 and 2019, until the apparently impermeable recent roadside surfacing is remediated.

There is no stormwater piping mapped on this side of the road, and we have observed no need for reticulation or detention of stormwater to date, with the vast expanse of mown grass and the forest below to absorb runoff which we presumed was, until the recent surfacing, running through the soil, and being filtered of at least some of the roadside contaminants, and providing much-needed water for the dry forest ridge margin.

We have been pleased to see nearly all trees, juveniles and seedlings in this area survive the present drought so far, and hope to see them develop to maturity, providing shade and lowering the ground temperature in summer both for the comfort of pedestrians and the health of plant life.

We hope for a simple and economical remediation plan by the restoration of widespread filtration and absorption by soil, by returning run off channels directly from paved road to permeable surface. Especially in the present drought, our restoration and the health of the forest and stream below are entirely dependent on winter rain.

Attempts to remediate present flooding and erosion by interference with the soil and vegetation on the steep bank of the current runoff channel would result in the destruction commonly observed to streams, estuaries and steep banks throughout the catchment as a result of channeling (earthen or concrete), piping, rock baskets or rip rap. Hopefully such solutions will not be considered.

This regular volunteer and Reserve visitor is particularly grateful for this recent filling of the deep rut along this part of the road edge, as the level surface between road and roadside berm now allows vehicle access to the roadside when approached from the North, by turning from the median strip instead of having to drive several kilometres via Beachhaven to arrive facing North to park and access the Reserve safely.

A speedy remediation might be channels in the roadside surfacing and if necessary immediate earthen channeling across the grass berm, to reclaim the winter rain for the upper part of the site, to avoid significant ongoing destruction of the restoration regrowth and planting, native forest below, and the Kaipatiki Stream and estuary.

This could be an excellent opportunity for low-cost community-supported vegetative filtration of roadside stormwater run off. We look forward to being further educated about the engineering possibilities for this situation, and sharing our detailed site-specific knowledge of vegetation, soil stability and run off patterns, towards the restoration of roadside permeability or channeling to the abundant vegetative filtration available directly from where this water leaves the road from about 20-50 metres further up the hill.

UPDATE After witnessing the current storm drain overflow from 100m uphill, we believe that with appropriate planting and wild revegetation, Gahnia Grove and adjacent forest margin could, without flooding or erosion, absorb and filter much water currently polluting and eroding the banks of Kaipatiki Stream within the forest.

We have seen many beautiful raingardens have been planted, but all that I have seen have been subject to non-selective herbicides before becoming obliterated by invasive weeds, the wet environment being conducive to vegetation of whatever sort survives the herbicides, often the most aggressive weeds. Gahnia Grove is a site-specific weeding project based on ongoing monitorihng, and could perhaps, with comprehensive planning, implementation and ongoing flow assessment in collaboration with Healthy Waters, provide an example of a successful stormwater absorption.

Current status of the situation should be available from Council using the Reference number 8160034765, for my call, which used the switchboard menu option Water Pollution. A contractor inspected the site with me shortly after, on Saturday 28 Jun, during intermittent light rain following steady rain which totaled 9mm for the day, had totaled 25mm in the previous 24 hours, and had not exceeded 32mm in 24 hours*. A light rain occurred during our inspection, and we then witnessed the roadside runoff flowing in meandering channels through and across the mown kikuyu pedestrian strip, and via numerous channels to 10mm deep through the recent planted native herbs, leaving many plants with all roots exposed and one or two floating.

An unsuccessful attempt was made to advise Parks, via Call Centre, of the current flooding of the roadside path, hoping to get permission and perhaps help to use a spade to channel at least some of the escaping precious water back towards the dry parts of the site, but after reaching Call Centre the first time we were accidentally cut off, and after waiting five minutes to get through again we abandoned the attempt, since there was no evidence of danger to people.

A short video made at the top of the bank shows water flowing through the native and benign exotic herbs currently replacing the kikuyu in Gahnia Grove's "kikuyu margin":

Some preliminary observations have been made of the effects of the runoff flow through the mown kikuyu and ex-kikuyu margin of CHF Bank , down the lower half of CHF Bank, through the forest below CHF Bank , and on Towai Bank, down to the boardwalk and stream below.

*Based on a domestic rain gauge 500m away. Metservice data for “North Shore” reflects its closest weather station at Whangaparaoa

Posted on June 28, 2020 00:22 by kaipatiki_naturewatch kaipatiki_naturewatch | 0 comments | Leave a comment

June 23, 2020

Climate maps show the drought, heat and sun on the North Shore

(And if you missed it, here is NIWA's explanation for the present drought:

It takes a little effort to learn to read and interpret the climate maps, but its worth it. We called NIWA recently for clarification of the Hotspot maps and the Soil Moisture Anomaly index, and learned that the Hotspot data is produced primarily for farmers rather than forest management, so publication of some data usually ends in late Autumn.

Posted on June 23, 2020 20:16 by kaipatiki_naturewatch kaipatiki_naturewatch | 0 comments | Leave a comment

January 22, 2020

Extension of the GG Methodology Trial to two adjoining areas of Eskdale Forest

Separate umbrella projects have been created for Gahnia Grove's extension further into the forest and further along the forest's honeysuckle-infested ridge-top margin at Glenfield Rd.

Tanekaha Ridge extends from the lower boundary of Gahnia Grove down through the regenerating "dry kauri ridge" forest to the top forest track.

Rimu Ridge extends the Trial into very weedy, wetter banks with distinct and diverse native streamside-community vegetation including extensive fern-beds invaded by honeysuckle, from Gahnia Grove's Northern border at the Flame Tree invasion, along Glenfield Rd to almost opposite the petrol station.

Reports covering all three areas of Gahnia Grove's Methodology Trial will continue to be published here in the Journal of the "Gahnia Grove - Site summary and discussion" Project. As always, discussion and the sharing of knowledge and experience is welcome here.

Posted on January 22, 2020 23:17 by kaipatiki_naturewatch kaipatiki_naturewatch | 0 comments | Leave a comment

December 25, 2019

Pinales and exotic pine and fir trees on Tanekaha Ridge

Here are some of the observations to date of Pinales in the Gahnia Grove restoration trial area and the
Pinaceae in the native forest of Tanekaha Ridge

We understand that many exotic pines were felled decades ago to facilitate regeneration of the present native forest. In some areas, scattered exotic pines currently contribute to habitat for numerous native species including orchids, through moisture retention, shade and weed suppression.

Plant diversity can be further increased with carefully considered partial removal of the pine litter to exposed areas in the margins, where it helps suppress exotic grass invasion and is especially valuable for moisture retention in summer when judiciously arranged around existing native seedlings of the acid-tolerant species common in this plant community.

Juveniles and seedlings allowed to mature will incur the significant - and to date prohibitive - cost of arborism once they reach a certain height, or threaten native vegetation and safety once they begin to drop branches.

Several seedlings found in the younger manuka margin of the forest are believed to be Douglas fir, which is apparently more shade tolerant than Pinus species and thus more of a problem in this situation. These seedlings are in the vicinity of a Pinus pinaster, Maritime pine, about 6m H.

It is understood that Resource Consent requirements regarding invasive tree removal are under review, and we look forward to learning how this will affect the removal of juvenile exotic pines from this area of regenerating native forest, and from its margins alongside recreational areas.

Our observations of this area suggest that pruning or removal should only be done if and when soil has regained its normal moisture after the current drought.. and only during autumn or winter, not only to avoid disturbing nesting birds but, even more importantly, to avoid destructive light invasion and loss of soil moisture during dry periods.

Posted on December 25, 2019 21:19 by kaipatiki_naturewatch kaipatiki_naturewatch | 1 comment | Leave a comment

November 28, 2019

November 24, 2019

To prune or not to prune in a dense stand of Haloragis erecta (Shrubby toatoa) with a few light-loving seedlings beneath

Recently enjoyed some discussion with a fellow restorationist about Haloragis erecta as a nurse plant for native seedlings, and whether the desne stand of toatoa that arose near the top of CHF Bank in gahnia Grove might have supported more development of the ti kouka and karamu seedlings beneath it if it had been pruned at some stage.

Having thought it all over both onsite and off, my conclusion is that light-loving seedlings under the shade of the interior of a dense toatoa stand would benefit from a bit of release, ie pruning the toatoa above them.

However, since such a large area had been cleared of shrub and vine weeds that you can't really go halfway with, the main objective last summer was to get ANYTHING not too aggressive covering the ground. The Verbena, carrot and oxtongue, with nightshades, did a splendid job, and the toatoa were a plus, along with the Solanum opacum, in that they were native so "permanent" cover.

Since the drought last year was from about February to June and the ground was only really wet for a few weeks, I would do the same again- ie make moisture retention the priority, for the existing few trees and the most benign of the exotics.

The seedlings that have developed to about 30cm are all either under trees or within 1m of the canopy margin at the bottom of the bank. The seedlings that developed under toatoa were also in partial shade from a recovering karamu gradually leafing up after release from honeysuckle, and they were on the outer edge of the dense toatoa stand, which is still sheltering them nicely, the exotics having been successively removed as the karamu leafed out.

Posted on November 24, 2019 03:55 by kaipatiki_naturewatch kaipatiki_naturewatch | 0 comments | Leave a comment

November 03, 2019

Kikuyu control for 2019

An earlier post in the Gahnia Grove - Umbrella Project journal has been updated with
this one, covering both the original Gahnia Grove site and its extension North.

Posted on November 03, 2019 19:31 by kaipatiki_naturewatch kaipatiki_naturewatch | 0 comments | Leave a comment

October 24, 2019

Time-ordered site-specific observation search result links

Links to time-ordered search results are gradually being provided on the top right of each sub-sites Project page. We will continue to add and refine these links to enable viewing of change over time in areas small enough, or with views similar enough, to enable comparison over time, observing the effects over time of factors such as natural regeneration, weather events, climate change, plantings, weed invasion and control, air pollution, Reserve use, and trampling during monitoring and maintenance.

Posted on October 24, 2019 06:23 by kaipatiki_naturewatch kaipatiki_naturewatch | 0 comments | Leave a comment

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 more diverse and 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.

Posted on October 23, 2019 10:06 by kaipatiki_naturewatch kaipatiki_naturewatch | 0 comments | Leave a comment