Gahnia Grove - Site summary and discussion's Journal

August 07, 2021

Kokopu spawn in Tradescantia

From a Stuff article today about gully restoration in urban Hamilton:

"This particular gully holds a remarkable population of giant kōkopu, which appear to be thriving in its stream’s clear waters. Perversely, they spawn their eggs in tradescantia, a notorious groundcover weed that is the bane of gully restorers everywhere. The tradescantia which fringes the stream provides the perfect spot for the eggs to mature before hatching the next time a flood reaches them. So for now, the weed stays."

Posted on August 07, 2021 01:10 by kaipatiki_naturewatch kaipatiki_naturewatch | 0 comments | Leave a comment

July 03, 2021

NY Times article about the infrastructure value of trees in urban areas - re increasing heat

This article echoes local observations of why despite planting, tree canopy continues to decrease in urban areas. It is interesting to note, however, the greater resources apparently allocated to tree maintenance in the city discussed, and the emphasis on ongoing tending of planted trees:
https://www.nytimes.com/2021/07/02/climate/trees-cities-heat-waves.html

Posted on July 03, 2021 22:05 by kaipatiki_naturewatch kaipatiki_naturewatch | 0 comments | Leave a comment

May 29, 2021

Progress report for Year 3

Less than 3 years since we began the Gahnia Grove Trial, the site is showing excellent results.

In summer it was hard to see the juvenile and seedling natives, hidden for their own protection among dense wildflowers, whose colour and diversity were enjoyed by Reserve users.

Kikuyu was eradicated from the initial Gahnia Grove site within about 5 months, and from a further 3 metre width of kikuyu-free ground added to the cordoned area last year, for aesthetics and practicality.

After cutting down, uprooting or mulching of most of the benign exotic herbs, the number and height of the resulting native trees, shrubs, herbs and groundcovers is now evident, and it is an ideal time to assess the results of the Methodology Trial, and to discuss how the skills and knowledge might be passed on to other volunteers in Reserves, particularly those challenged by kikuyu.

Mass weed invasions were mostly Japanese honeysuckle, Tree and Chinese privet, Cape Honey Flower, Moth plant, Elephant’s ear (Alocasia), Kahili ginger, Arum lily, pampas, wattle, Elaeagnus (severl over 10m in spread, climbing several metres high into canopy trees, and some bushy small trees with trunks to 10cm D and 3mH), blackberry, Syzygium spp, Euonymus japonica, bindweed, Flame Tree, and Tradescantia.

The environmental weeds in Gahnia Grove have mostly been eradicated, or almost eradicated:

  • occasional remaining honeysuckle or blackberry root becomes apparent here or there a few times a year
  • all Cape Honey Flower stumps are now well-decayed
  • all pampas are dead, the largest pampas having had its last few weak live leaves in autumn 2021
  • moth plant seedlings continue to reduce in number each year, and no longer occur in the areas of the first invasions discovered and treated
  • Alocasia has not been found since 2019 except as one or two gradually decomposing but still live pieces of cut stem, which are kept free of the ground as they continue to die
  • the remaining live tubers of ginger and Arum are easily suppressed once or twice a year with deep piles of Tradescantia, which is still being retained in the area surrounding them, with ongoing control to be coordinated with the as-yet unknown timeline for arborist control of the Flame tree.
  • several Elaeagnus, the commonest of the tree weeds, remain as 10cm D tree stumps, with live shoots easily suppressed annually. The majority, however, are now insignificant amongst native vegetation, as broken-down, spindly stems, struggling to produce occasional foliage on their few live branches, after having been allowed until recently to continue producing this small amount of shade during the times of severest drought. They are easily further reduced once or twice a year in during ongoing survey and monitoring. Smaller specimens and those most intensively reduced have already died, and are present only as broken leafless stems identifiable only from our iNaturalist records.
  • Hundredss of Tree privet, Chinese privet, Cotoneaster, Euonymus japonica, Prunus serrulata (wild cherry) and Syzygium have been effectively suppressed. The first discovered and addressed, the tree and Chinese privets, have died and are now decaying, now hidden in the canopy margin among the spreading mapou, Coprosma, hangehange and Gahnia, or as isolated stumps invisible in the shade of the forest.

The hypothesis of the faster demise of woody weeds through leaving trunks and branches partially or (with ringbarking) wholly connected, forcing the tree to feed the upper part while preventing or reducing the downward transfer of nutrients to the root, has been supported by our results, and correspondence with more experienced overseas restorationists through iNaturalist supports the technique, and provides technical explanation.

Flame trees in the canopy and on its margin have had low and prostrate branches pruned, several small trees have died and their decaying bases uprooted easily. Two small stands in the native canopy margin, comprising four tall but slender trunks, have been ringbarked after inspection and authorisation by the Community Ranger and Arborist.

Tradescantia has been mostly removed, ie as much as current soil moisture levels permit, from most of the canopied area, and controlled on the steep sunlit banks above: CHF Bank, now mostly covered by young native trees and shrubs, and Flame Tree bank, where a fallen Flame Tree c. 15 gm H x 40cm D, still live but weakened by ongoing suppression through partial cutting through of branches, has been gradually reduced since Dec 2019 to the lower half of its trunk and one major branch. Most of the removed material has decomposed already, and the remainder is contained, decaying in a single loose pile on high dry ground.

The forest beyond its sun-exposed margin has been thoroughly weeded and is producing many seedlings of species found in the older forest, including many totara and tanekaha, with occasional rewarewa, kauri and kahikatea.

In the third year of the Trial, very little time has been needed for the control of environmental weeds in the initial Gahnia Grove site, while much time has been spent in maintaining and creating soil moisture and shade, and in monitoring and assessing the results of techniques and strategies used to date.

In the same time period throughout the combined area of the Trial - Gahnia Grove (begun June 2018), Tanekaha Ridge (begun June 2019) and Rimu Ridge (begun August 2019) - less time has been required for weed control than for the mitigation of increased heat, sun and drought, through the application of weeds as mulch and the creation of biodegradable shade-screens constructed from plant materials provided by the site.

Benign exotics retained for shade and shelter of regenerating natives have in Autumn 2021 been almost entirely culled, with the exception of Plantains which provide excellent small ground cover between natives and compete splendidly with kikuyu at the mown edge.

Depending on rainfall and sunlight intensity in the coming seasons, the currently established native revegetation, with the recently constructed screens of bamboo poles and harakeke prunings in the ridgetop areas exposed to afternoon sun, may provide sufficient shade and shelter for the continued successful development of seedlings and juveniles. If necessary some Verbena, oxtongue and wild carrot will be allowed to regrow where needed.

The kikuyu technique, in particular, has been surprisingly effective in eradication, more time-efficient than expected, and would be very valuable in the preparation and maintenance of both passive restoration and plantings.

One major cost benefit of the method is that, since the released area is immediately plantable and free from reinvasion, much smaller plants can be successfully planted. This has been shown by several 4-10 cm H tree, shrub and grass seedlings planted in early summer 2020 within 30 cm of the mown kikuyu, in May 2021 they remain weed-free, and are now 30-40cm +H, robust and vigorously growing, some in full sun and some shaded by other native herbs and shrubs.

The mown sward will of course require ongoing control along the edge. Methods we are trialling are aimed at inhibiting the invasion where shade is not yet, or is not planned to be, established.

Particularly helpful so far have been dense plantains, (both broad and narrow-leaved). We have yet to see the establishment at the mown-edge of the creeping ground cover Nahui, and the native grass Microlaena stiploides.

Among the trees, mapou shows the most drought-tolerance, resilience to damage and disease, and dense, light-excluding foliage from ground up. Thus in the remaining treeless areas near the top of the ridge we are aiming to provide the conditions most suited to mapou seedling establishment, with initial ground cover by the prolifically germinating, quick-growing, but short-lived karamu.

Posted on May 29, 2021 22:00 by kaipatiki_naturewatch kaipatiki_naturewatch | 0 comments | Leave a comment

March 25, 2021

Wasps in the roadside areas of Gahnia Grove

There are a huge number of wasps in the sunlit area alongside the road opposite 227 Glenfield Rd, foraging on the ground and entering the rawirinui in the canopy, only about 4m H here. Densities in sunny periods are such that we dare not disturb the ground litter and mulch, which we know covers many cracks in the ground after prolonged soil moisture deficit, and care has to be taken, walking slowly and scanning, to avoid bumping onto them, with several passing each second at times.

Contractors for Council have removed two small paper wasp nests from beside the cordon where they were encountered while pruning a toatoa and low branches of a totara. A search of the surrounding area by the contractor has not disclosed any Vespula wasp flight paths of sufficient density to indicate immediate proximity of a nest, and we have now asked Council to bait the area with Vespex, since protein foraging activity appears to be high, and the likelihood of nests overwintering is extremely high in this location where temperatures remain high throughout winter.

Any progeny of the forest gecko will be vulnerable to wasp predation, the high invertebrate populations nurtured in the restoration area are probably being consumed right now, and birds as well as reptiles will suffer from the competition for nectar.

We ponder the impact of the wasps on the high numbers of plague skinks in this sunny area of deep dry mulch, where these tiny lizards scuttle constantly away from vibrations of our footsteps.

A sugar water wasp trap has been made according to a beekeeper's youtube video, with vinegar to discourage bees, and detergent to reduce buoyancy of any wasps trapped. We dont expect this to reduce numbers noticeably, but it may help indicate the numbers present.

Posted on March 25, 2021 20:35 by kaipatiki_naturewatch kaipatiki_naturewatch | 0 comments | Leave a comment

January 29, 2021

Planted harakeke bordering the forest margin

Harakeke in Gahnia Grove

A lot of detailed observations and questions regarding the harakeke in Gahnia Grove, were not addressed in the Annual Report for Year One or Year Two pending a fuller assessment of their interactions with the trees around them, and the results of pruning. We still hope to learn about their impact on water distribution on a dry ridge after deforestation and roading, but in the meantime we can report on their ongoing management, in these two areas:

Gahnia Grove “proper” (site adopted in June 2018)

The three large stands at the top end of Gahnia Grove are very old, contained many dead plants and in places had forced trees horizontal for up to 3 metres, with live harakeke plants lying horizontal on the outer edge of the ring, on tall bent roots overlying up to 50cm depth of dead plants.

Initially we were able to maintain the natural, unpruned harakeke form of these stands, with long leaves flowing to the ground, but as the plants multiplied the new leaves protruded over the cordon. Despite pruning of outer leaves and flower stems to 4m long overhanging the cordon and obstructing mower and pedestrians, they regrew rapidly, with new plants continuing to emerge at lower and lower angles.

As each successive outer ring on the growing clump emerges at an increasingly horizontal angle, the dead mass or vacant space in the centre of the clump grows larger with the death of each generation of plants in the clump. We have been watching with interest what seems to be the terminal development of these old stands (probably the remains of the 1999 NSCC planting), while trying various methods of preventing them from impeding the growth of the surrounding trees, which are desperately needed for shade of the forest margin behind.

Until shaded out by tree development they will require perpetual weed control and pruning. Weed control is not an issue within Gahnia Grove where kikuyu and vine weeds have been eradicated, but pruning needs increased as each clump grew additional plants each year.

The options have been either to widen the Trial area (exposing more bare ground until native vegetation grows) or to trim the leaves.

We intially trimmed them to fit the cordoned area, but the cut leaf edges became a hazard - and unsightly - as the cut leaves grew. We now cut them very short where possible, but this still results in unsightly cut edges that eventually protrude over the cordon.

Extending the existing band of dense trees, from the top end (open grass area) down towards the flame tree, is the goal for the entire kikuyu margin, to shade out weeds till maintenance requirements are minimal (as in the 10 m of kikuyu margin with dense tree development, ie the Annexe Kikuyu Margin, at the Southern, uphill, end of Gahnia Grove), and for support of the forest reveg below, as the 25 metre wide treeless area is the hottest location on the ridge.

However, whether this can be achieved is uncertain due to the natural aridity and podzolization of this dry kauri ridge, the dessication and growth-inhibiting air pollution common to roadsides, the higher temperatures currently being experienced due to climate change, and hydrological and/or meteorological drought since January 2018.

The few trees that existed here in June 2018 were so heavily covered by honeysuckle that, though they started to leaf out on release, several did not survive the subsequent drought. In the 25m of Arena Kikuyu Margin and CHF Kikuyu Margin, the two harakeke stands have been the only wind-break and shade, and the shade of harakeke will of course remain low, ie 2-3m H. The areas directly below these harakeke stands are also the two driest areas, struggling to produce even wild carrot or ox tongue. During ongoing observation this Winter I have been wondering whether this is due to unseen underground water runoff patterns or the success of harakeke in absorbing the water as it comes down the hill. If the latter, this high point on the ridge may do better after the natural demise of the existing harakeke stands, provided alternate shade has been established by trees. This will be a challenge to achieve while the drought continues.

Due to the uncertainty of adequate rain, the priority of the 2020 workable season, ie winter, was to trial ways of creating shade, including placing bamboo poles and kanuka brush in soil before it became too hard to do so. The resulting shade-fences and shade-tents potentially allow shade to about 2mH from native vines (Ipomoea was removed from the plan after further research led to discussion with Ewen Cameron, but some wild rauparaha, sourced from the nearby forest-margin raingarden, was planted here, the invasive bindweed hybrid having been virtually eradicated over the last 2 years) and/or harakeke shade tents. Loose, natural-looking shade tents (with varying degrees of visual appeal as we discovered what materials and arrangements were stable enough to stay in place in high winds, dense enough to provide shade without creating wind resistance. and sufficiently robust not to crumble before the summer was over).

Several such arrangements of vegetation were successful last year in alleviating critical drought stress for specific trees on the canopy margin exposed to sun by the cutting of honeysuckle vines in the trees.

Harakeke in Rimu Ridge (from the Flame Trees to the Petrol station, adopted for care and included in the Methodology Trial from August 2019)

In the margin of Rimu Ridge the harakeke-dominated banktop was adopted only because it was part of the invasion of honeysuckle and moth plant binding and smothering the trees both at roadside and within the forest margin from ground to canopy, including almost all the juveniles and adults visible from the kikuyu margin since their release, all those down the bank below, and many within the taller rawirinui/podocarp canopy behind that.
Some trees found in the honeysuckle were already dead and others partially dead. Several of the dead trees have since fallen down, and the partially dead have been pruned, where possible and as time permits, to live wood).

This forest restoration trial is intended to demonstrate the long-term economy of a chemical-free weed control methodology, enabling a natural forest succcession through selective weeding over a period of years, culminating in weed eradication and reduced potential for reinvasion with the development of shade (a fundamental principle of forest restoration). Once sufficiently dense shade and intact native plant communities are achieved, minimal ongoing maintenance is required. This principle of establishing shade underpins the Gahnia Grove trial, including the eventual suppression of kikuyu at the mown edge, so that spraying, linetrimming or manual control are no longer required except where light breaks occur, eg due to a tree death.

While releasing the mature trees of the rimu ridge forest margin from honeysuckle we undertook the management of the very, very many harakeke that were uncovered there, including

-small to medium single plants

-small and large groups of small to large plants

-an outer row of small separate plants, many of them with damage or dead due to a single herbicide overspray event in l2019), a few of them projecting into the mown area from an otherwise straight line, The inclusion of these necessitated extending the cordoned area outwards, beyond what would be ideal for the aims of the Trial, and they were included only because they would otherwise impede mowing, and prevent kikuyu control.

-older plants both in large tight groups up to 10 metres across (with honeysuckle rooted throughout, eventually reached as older harakeke plants collapsed), and scattered throughout, with empty space or isolated trees both live and dead in between.

Posted on January 29, 2021 00:02 by kaipatiki_naturewatch kaipatiki_naturewatch

September 26, 2020

Record dry spells and effects on forests

From https://www.scoop.co.nz/stories/SC2002/S00030/record-dry-spells-and-effects-on-forests-expert-reaction.htm:

"Associate Professor Cate Macinnis-Ng, School of Biological Sciences and Te Pūnaha Matatini, University of Auckland, comments:
“We often think about the devastating impacts drought can have on agriculture but forests and other ecosystems also suffer under drought. Around the world, there are growing records of forest dieback due to increasing frequencies and intensities of drought due to climate change. Here in Aotearoa, droughts don’t generally cause forest death because our droughts last months rather than years.

“While there are some examples of forest death due to drought in the literature, our ongoing research on kauri suggests their deep roots, stem water stores and conservative water use make this species well-prepared for dry periods.

“However, in the 2013 drought, we found that litter fall increased in kauri forest as kauri trees lost leaves to reduce leaf area and therefore save water. This type of response may complicate ongoing efforts to use remote sensing techniques to detect kauri dieback but continuing work at our experimental drought plot will help us tease apart canopy changes due to drought from canopy changes due to dieback.

“Interactions between kauri dieback impacts and drought are not clear. Dry conditions may prevent spread of the pathogen but when rain does arrive, trees weakened by drought may be vulnerable to infection.

“Established forests may be relatively safe from drought impacts, seedlings and restoration plantings are vulnerable as developing root systems of smaller plants do not have access to deep soil water stores. If drought continues for extended periods, carbon uptake may be reduced as plant productivity slows.

“Drier plant tissues are also more flammable so we all need to be especially careful with fire. The recent forest fires across Australia were exacerbated by drought and severe fire weather across large areas. While we are unlikely to suffer such catastrophic events here, we still need to plan carefully to protect forest and manage our water supply."

Posted on September 26, 2020 12:04 by kaipatiki_naturewatch kaipatiki_naturewatch | 0 comments | Leave a comment

September 11, 2020

Forest Gecko - Guidelines for land management

The information below is copied from https://rarespecies.nzfoa.org.nz/species/forest-gecko/

"Association with Plantations
Forest geckos have been found associated with exotic forestry in Northland, Auckland, Spooners Range, Nelson and on the West Coast.

Management Options and Methods

Maintain wide and interconnected zones of potential lizard habitat, e.g. indigenous forest and shrubland, rocky gullies, cliffs and other distinctive habitat types.
Create buffers around known habitat.
Consider permanent protection of known habitat.
Comply with best forest operational management practices to avoid damage to lizard habitat.
Fell and haul timber away from lizard habitat.
Exclude livestock from lizard habitat.
Control possums, deer and goats that could enter lizard habitat.
Raise awareness of staff and contractors of the presence of lizards and the need to protect them.
Monitoring Options
Take photographs or write a detailed description when lizards are found. This can be used for later identification.
Survey for lizards, particularly if first time planting is being considered for the area. Note that planned surveys require a permit under the Wildlife Act (contact DOC for survey methods and permits).
Maintain database of sightings of threatened lizards and liaise with DOC.
Report findings to DOC"

Posted on September 11, 2020 00:24 by kaipatiki_naturewatch kaipatiki_naturewatch | 0 comments | Leave a comment

September 09, 2020

Forest Gecko seen in Gahnia Grove

The location has been generalised in our iNaturalist observation to avoid disturbance or theft, so it won't appear in the data for the restoration trial or the area generally, but it was thrilling to see a gecko in the outer manuka margin, a couple of metres away from where I was handweeding an area of dense Bulbil Watsonia, and only about 10m from the mown recreational grass much enjoyed by dogs and their owners.

Be safe, little gecko. Climb back down into your man-made hole and find a bottle or something too small for rats, to hide in at night. (Note to self: don't remove any more isolated bottles and cans from the forest).

UPDATE: DOC was advised, as requested on heir website, and an appreciative reply was received, with more information to follow. DOC collect data to build knowledge of the remaining population of these endemic reptiles. Currently they are considered At Risk of extinction, after being common in manuka scrub throughout Auckland until the housing boom of the 70s.

Fortunately Reserve visitors generally keep themselves and their dogs to the recreational mown grass area and the forest tracks. However, responsible dog owners ensure their pets have energetic and interesting exercise, and many if not most dogs are off-leash as their owners accompany them through the winding forest tracks.

Protection of the remaining endemic lizards in both the DOC-owned upper forest and estuarine areas, and the Council-owned forest in-between and surrounding them, would require definition of boundaries for recreational and conservation.

Due to the presence of both domestic and feral cats, which, as I observed 30 years ago in the case of my own beloved pet, can effectively eliminate lizards from the forest, areas of cat-proof vegetation are essential to maintain as habitat. Weeds such as dense Eleagnus, blackberry, honeysuckle, jasmine and ivy, and the extensive and widespread inorganic refuse, need to be replaced by equally effective protection for lizards, invertebrates and birds before the complete removal of refuse or weeds.

Ground litter and dead vegetation is especially important as part of their habitat. Welll-intentioned clearing and tidying of vegetation leaves reptiles, invertebrates and young birds without refuge from predators and human disturbance.

Posted on September 09, 2020 23:52 by kaipatiki_naturewatch kaipatiki_naturewatch | 0 comments | Leave a comment

September 08, 2020

Some research on Bulbil Watsonia

At last we understand the life cycle whose manifestations we have been witnessing since May 2018 throughout the manuka forest margin, and it confirms the suppression of native regeneration through dense soil occupation by corms, despite the failure of the weed to flower in this partial shade: http://www.herbiguide.com.au/Descriptions/hg_Bulbil_Watsonia.htm

On initially observing this forest margin, juvenile and seedling manuka, kunzea and native broadleaf or podocarps were rare in the 6 to 8m H dense manuka canopy, with an understorey only of dead manuka. We feared the forest succession from manuka to kanuka and then forest trees might not occur, and instead the pampas, gorse, Watsonia, Aristea and other weeds might take over this 150 x 10m of land, which had been dedicated to the extension of existing podocarp/rawirinui forest regeneration by the cessation of mowing several decades ago..

If the intended natural forest succession does take place, it may never be possible to determine what would have happened without control of the Watsonia and pampas, since the entire area has now been at least partially hand weeded for 1-2 years, and leptospermeae are germinating and developing in released areas, often seen directly alongside the annually winter-growing Watsonia leaves during their control.

But we may be able to learn the effect of the method and timing being used in the control of Watsonia, both in the filtered light of a broken manuka canopy, and in the partial shade of the outer manuka and rawirinui margin, in previously-mown grass where in 2018 it was flowering and reproducing through cormils.

Posted on September 08, 2020 22:30 by kaipatiki_naturewatch kaipatiki_naturewatch | 0 comments | Leave a comment

July 23, 2020

Year One Report reformatted

The Year One Report has just been updated with the improved formatting now possible in iNaturalist for non-programmers like myself, making the report easier to read and navigate. The process of review was illuminating, as we realised how much of the weed control has become "history" already.

While reviewing the one year summary we slightly changed some linked searches to limit the results to observations made in Year One, since, as in our other posts, most searches update automatically to include any subsequently uploaded observations.

We also edited the text slightly in places for clarity, and changed Field Values in a few cases to improve the selection of observations selected to illustrate a habitat, technique or results.

The Year Two report, already getting buried under more recent posts, is here.

Posted on July 23, 2020 03:23 by kaipatiki_naturewatch kaipatiki_naturewatch | 0 comments | Leave a comment