יומן של Gahnia Grove - Site summary and discussion

ארכיון יומן של יולי 2020

יולי 5, 2020

Campsite and rubbish tip found in forest

About 20m North of our Rimu Ridge site, hidden in the forest below the petrol station, we found this after spotting something large and blue among the trees, (while checking for flowering among a group of trees which, if wild, are the first recorded observation of the species wild in NZ - but that is another story).

הועלה ב-יולי 5, 2020 09:40 לפנה"צ על ידי kaipatiki_naturewatch kaipatiki_naturewatch | 0 תגובות | הוספת תגובה

יולי 17, 2020

"El Riachuelo" - the ephemeral steep forest stream of Rimu Ridge

Thursday 16th July 2020

A juvenile treefern (left) and Gahnia xanthocarpa (upper right) released from palmgrass (part of the retained portion visible at upper left) on the South (El Sitio) bank of El Riachuelo

{UPDATE July 27
Several forays into the surrounding forest below the flooded area revealed no plant material or litter associated with recent flows. The flow seems to have been widely disseminated by fallen logs and deep pine litter, both of which will be maintained to ensure ongoing absorption here near the top of the ridge in the wet-loving plant community that has developed there.

The streamhead has been loosely covered with available dead woody vine, dead branches and cut harakeke tied into bundles. The stream channel below has been bridged at close intervals with fallen branches, and these will be covered by cut harakeke leaves, including some coarsely woven mats to allow filtered light and easy uplifting for water inspection.}

Videos 1, 2, 3, and 4 were made of the stream on Sunday 21 July, after 5mm of rain that day, and 2mm the day before (recorded by rain guage at a nearby residence).

At the dry start of an even drier summer last year, during exploratory weeding near the top of the newly-adopted forest margin at El Sitio, we were uplifted by a tiny glimpse of standing water beneath dense palmgrass under native trees recently released from honeysuckle. The small area of palmgrass removal revealed mahoe and kawakawa seedlings and a tiny fern clinging to a low wet bank. A hidden roadside drain, we thought. Or run off from recent rain somehow channelled and briefly pooled here. Half in jest, we named it: "El Riachuelo", or "The Rivulet". Like "El Sitio", the restoration area between this water and the mown grass margin, the name honours the native language of the volunteer who has adopted the care of this area.

This week, removal of much of the palmgrass foliage revealed an ephemeral first-order stream, a significant part of the urban Auckland freshwater environment.

Satellite view of the canopy development from 1960 to the present day suggests, at some time in history, two confluent streams in Gahnia Grove. The site of recent erosion by stormwater runoff, "Forest below CHF Bank," appears to be in the vicinity of the Southern of these streams, while the satellite-view suggests a Northern arm running down from the palmgrass infested area just South of the petrol station, the two streams meeting at the boardwalk of the forest path.

The manual suppression of about half the palmgrass infestation in El Sitio disclosed the head and about 10 metres of an ephemeral stream. Of low gradient and energy here at the top of the ridge, it meanders across the bank, disappearing under log dams and coarse forest debris in places, before separating into separate channels, some of seepage, some contributing to a steep forest stream below.

At its head it emerges from solid ground at the lower edge of El Sitio Top, ie about 10m within the cordoned Trial area and over 20m from the undrained roadside. Over its emergence the ground is clay, bearing mature trees and apparently stable. There is no piping, channelling or other sign of construction at the stream's emergence, though a section of plastic corrugated drain is partially embedded in the soil there, perhaps, like other construction debris and litter throughout this roadside forest margin, discarded at roadside and blown or washed down the bank.

Under the water at the bottom of the a short 2 m deep, 1 m wide channel of the stream's emergence are one or two flat slabs of rock or possibly concrete.

Today after light rain the stream is flowing gently and steadily between its banks, the ground on either side porous and superficially moist, with native tree seedlings and juveniles undisturbed. The left bank, a broad shallow slope, has evidently been uniformly flooded at some time or times between Tuesday and Thursday, throughout several metres of its breadth, to a height of about 30cm, leaving debris over a decaying long-fallen tree (wattle?) and a dozen or so suppressed palmgrass plants, among which the few native plants found were nikau seedlings and Carex lambertiana or dissita. There are no plants uprooted, either by weeding or by flooding, and the visible debris ends at the lower end of the palmgrass stand, where small hangehange, mapou, coprosma, putaputaweta and Syzygium stand several metres tall, undamaged, and the remaining palmgrass hides any debris or channel.

Beyond the palmgrass the bank slopes steeply downhill, and in places a narrow unstable channel can be seen descending it through a dense diverse mainly-native understorey partially released from honeysuckle from late 2019 on. Since the adoption of El Sitio into this Trial, the Kahili ginger dominating this understorey on adjoining banks is also being progressively reduced, but much remains.

At the stream's emergence the bank is a steep slope on both sides, the water emerging a metre or two below the bank top. A few metres downstream however, the stream banks are lower and the surrounding ground almost level. The stream remains 10-30 cm deep as it runs between shallowly undercut but stable clay banks, bordered by flat slightly spongy ground with a homogenous fine black tilth at least 10cm deep, with some substantial mahoe and putaputaweta roots in the stream channel itself. The vertical and undercut banks of the stream are moss covered and bearing juvenile ferns in some small areas where a little exploratory weeding was done in late 2019, before halting weed removal during the dry season.

As the stream turns South to meander across El Sitio Bank, a shallower branch runs straight ahead through the litter of a large radiata pine on Pohutukawa Bank. Past this pine the current becomes widespread seepage and puddles, with a thin trickle turning left to rejoin the stream on El Sitio, where it is hidden under the remaining stand of palmgrass.

Nikau seedlings and carex lambertiana/dissita and ground mats of thread fern (Blechnum filiforme) are present here wherever palmgrass is absent. (Thread fern also climbed the trees and covered the ground further uphill on the periphery of the recently flooded area until seriously declining in late summer 2020 after prolonged severe drought).

The reduction of the palmgrass infestation two days ago in El Sitio did not involve uprooting plants. Each of a dozen or so very large plants had its seedheads tucked down into its centre and its leaves broken down and pressed onto the base. These manually controlled plants are now about 30-40cm H, spaced 50-100cm apart and topped with a little flood debris.

The steep banks of the stream's emergence currently hold flood debris to about 1m above ground level on each sides of a 2m deep, or high, erosion of the clay bank, suggesting water emerges at its base, or flows over its top, with some force. There is no sign of flooding on or over this bank however, so we assume the flow is from underground, either from a broken stormwater pipe - although we understand there is no reticulation of stormwater on this side of the road - or an unformed underground channel or spring.


Assessment

There is no sign of flooding or boggy ground above the emergence, ie from the roadside to the head of the stream. Therefore we assume the stream emerges with some force and volume from an underground channel, whose source is unknown, and has supported the development of this streamside plant community for several decades. The exposed 10-15 m length of stream currently meandering across the bank irrigates the porous and humus-rich ground around a mature and a juvenile nikau, several mature, but drought-damaged, putaputaweta, several large mature pigeonwood, mapou and mahoe, which together form a thin and incomplete canopy.

There are few intact fallen nikau leaves. As the nikau is about 8m H and there are few intact nikau fronds, we assume that several decades of fallen palmgrass and nikau leaves have rotted here, with the abundant ti kouka leaf litter, in the seasonal flooding of this stream, creating the spongy, fibrous soil. Perhaps the stream also brings sediment from erosion of soils elsewhere. In any case, the vegetation seems to have been effective in filtering a good deal of water while developing and retaining a rich and absorbent soil.


Plan

Beyond the area of this week's palmgrass control and stream exposure, tree canopy is thin here. Though rawirinui and radiata pine provide tall canopy on the left and right, summer sun falls directly on this area for parts of the day, threatening dessication. The stand of palmgrass that remains here is mixed with small trees, and will be retained (with seedheads controlled) until the exposed area above has been revegetated and the stream shaded, initially by small logs and nikau fronds placed across it.

Decaying fallen and woody debris will be placed in the stream where they are likely to slow flow and create pools without being washed away.

Logs, sticks, nikau fronds, ti kouka leaves and other woody debris will be placed across the broad almost-level flood-prone bank, trapping debris, to retain maximum soil moisture for both wild and small planted seedlings to reestablish ground cover after the loss of palmgrass cover. The flood pattern will be determined by observation of the movement of this debris, and its placement adjusted for maximum debrism soil and water retention accordingly.

The many clumps of still-rooted palmgrass are continuing to slow flood flow and trap debris, and will be retained, with their foliar regrowth possibly being encouraged through next summer, to be further reduced next autumn.

Runoff patterns, flooding depths and signs of erosion will be monitored to guide further restoration.

Research for Auckland Council has determined that ephemeral steep forest streams are an important habitat for shortfin eel and banded kokopu reproduction, though adults may not survive the summers. This ephemeral stream feeds into the Kaipatiki Stream about 50m downhill. It would therefore be very helpful to know how contaminated this water is, and whether it contains life.

Pending any further advice that may be received, a provisional plan for protection of El Riachuelo's "flood plain" has been posted here.

הועלה ב-יולי 17, 2020 11:30 לפנה"צ על ידי kaipatiki_naturewatch kaipatiki_naturewatch | 3 תגובות | הוספת תגובה

יולי 21, 2020

Learning from the ridge-top "flood plain" of El Sitio

Palmgrass reduced under mature porokaiwhiri (foreground left), putaputaweta, nikau, mahoe and mapou

An earlier post on the ephemeral stream "El Riachuelo" is here


UPDATES

20 October 2020 Having now attended a course on freshwater ecological testing offered free to the public by PestFree Kaipatiki, we hope to be able to test the water using their testing kit before the ephemeral stream stops. If this is not possible we will test it in Autumn 2021.

October 2020
About a dozen seedlings of Haloragis erecta (toatota), Esler's groundsel (Senecio eslerii) and kawakawa, none taller than 10cmH, were planted on the stream banks where ground could be easily disturbed with a small trowel without encountering tree roots. The area remains well-mulched with decaying plant material, mostly palmgrass.

The stream stopped flowing during a dry early Spring, but has been inundated once or twice since by rain events. The stream continues to flow for at least several days after rain.

The few wild native seedlings and sporelings (including a mamaku c.30cmH) that were revealed by palmgrass reduction have survived subsequent drying and flooding, and leaf litter is arranged around them to retain moisture after each flooding.

The upper portion of the stream remains hidden by the material placed earlier across its banks, ie dried fallen nikau fronds and small logs supporting a loose tangle of dried woody honeysuckle vine.

The bank over the stream's emergence remains exposed at the top, as small Pteris tremula (shaking brake) and a few native tree seedlings have successfully established there. The juvenile karamu and mahoe growing on the top of this bank,and potentially shading the streamhead, have been mulched with woody weed material, and partially sheltered and shaded with a screen of bamboo poles and harakeke leaves, and the young trees are currently doing well. If their growth can be maintained they will supplement the streamhead's partial shade by a wide-spreading rawirinui about 10m H, released from dense honeysuckle in Oct 2019. This forest margin is exposed to the North and East, remains dry from the current drought, and will remain sensitive to sun, heat and wind during the coming summer.

July 29
Small logs (.5 to 1 m long) of recently-cut (home tree-pruning) kohuhu and kanuka have been placed across the stream channel throughout its length, interspersed with a few larger fallen logs, between the ti kouka and putaputaweta trunks, newly arisen fern sporelings and a few Coprosma seedlings, leaving these with access to light while keeping the soil shaded. These logs have been covered with lightweight carbonaceous shading materials including cut honeysuckle vine, fallen nikau leaves, kanuka/manuka brush and cut harakeke leaves. As summer proceeds the shade materials will decay, be replaced and added to with more harakeke leaves, which are abundant as the hundreds of individual plants on Rimu Ridge continue to multiply and need pruning to release adjacent juvenile trees.

Some shorter fresh logs have been placed in the streambed to slow flow, which diminished to 1-10cm depth after the rain, and is no longer evident as overland flow down the adjacent banks, though its Westward path is still wet, about a metre wide and meandering through the pine litter down Pohutukawa Bank and the forest below.

Further exploration found no channel, erosion, flooded plants, or plant material or litter associated with recent flows. However, a rough erosion channel has been seen in that general area when looking up from the forest path below the big rimu, and it is possible this overland flow contributes to that channel.

The flow, both recent and historic, seems to have been widely disseminated across El Sitio by fallen logs and deep pine litter, both of which will be maintained to ensure ongoing absorption here near the top of the ridge in the wet-loving plant community that has developed there.

The streamhead has been loosely covered with multi-branched small dead karamu, dead woody vine, and loose harakeke. Some coarsely woven harakeke mats are planned at one or two points, to allow filtered light and easy uplifting for water inspection.

Fauna:

Rotting logs have been moved in places, to lie across the bank rather than up/downhill, but they are not placed in the stream as they are invertebrate habitat, not to be disturbed. These logs are themselves being covered with loose vegetation to maintain habitat.

Birds and invertebrates will be able to access the stream in gaps between the shade materials, to be left more open where there is tree canopy, and removed as streamside vegetation develops.

Rubbish:
There is little rubbish in the stream -

a disposable medical mask
and a Coke bottle (glass) and a Coke lid (plastic) being among the few items found on the bank, and none in the channel. Newly arriving litter in the stream will be removed before it becomes habitat, unless we are advised to the contrary.

Under remaining palmgrass in the floodpath several large plastic planter bags were found, containing nursery plant medium and some obviously self-sown native carex. The carex will be planted, and the bags removed.


Background:
The presence of a wet-loving streamside community
here surrounding an ephemeral stream near the top of a ridge is of great interest. While on either side the soil is dense clay, the 10x10m of ground found here almost totally occupied by palmgrass is topped with a fine black tilth at least 8cm deep, the depth and area of this soil to be further explored.

The area begins 10m downhill of the emergence of an underground stream on El Sitio Top, and is the site of recent, and presumably historic, widespread surface flooding after heavy rain.

The flooded area ends downhill at the top of a steep bank of scattered large rawirinui just outside the dripline of a large radiata pine to the North on Pohutukawa Bank, with partial canopy by mature kohuhu, mapou, porokaiwhiri (pigeonwood) and nikau, a 6mH Syzygium (monkey-apple) and an understorey of karamu (Coprosma lucida, macrocarpa minor and robusta), hangehange and mamangi (C. Rhamnoides) with many separate dense carpets of thread fern, some in shade and some sun-exposed, all moderately infested with honeysuckle, ginger and juvenile Syzygium. (This bank is outside the Trial's boundaries, and not publicly visible or easily accessible).

At the bottom of that steep bank is a large bare area of pine litter below the pine, above an old rimu with diverse streamside-community understorey and ground cover forming the lush and attractive border of the public path through the forest as it descends towards the wider Kaipatiki Stream formed by the confluence of several tributaries along this ridge.

Was this patch of deep, rich soil a naturally silt-trapping niche on the dry ridge prior to the felling and possibly burning of the forest for European forestry and farming? Or was it a steep forest stream, ephemeral or possibly even perennial due to a spring, which, once invaded by palmgrass, slowed flow and retained silt sufficiently to create the deep, rich seasonally inundated soil supporting thee mature putaputaweta, nikau and ti kouka?

Dead decaying trees here indicate canopy over this area, possibly of wattle, lost in the last 20 years.

We appear to have in this 100 sq m a model of waterquality, soil and biodiversity protection in an urban area already subject to air, water and soil pollution, with potentially significant erosion and deforestation.

Through regular monitoring of the results of our suppression of the palmgrass plants and restorative interventions on this site hope to learn how to assist El Sitio's ongoing

  • retention and absorption of water
  • development of such rich, moist soil
  • restoration of dense ground cover as quickly as possible, by nurturing existing, and planting or sowing additional, native seedlings and ground covers (eg the species listed below)
  • development of complete canopy by supporting the development of native trees surrounding it and arising in the mini-floodplain

The immediate goal is to shade the stream and the exposed bank between the stumps of palmgrass plants, using available material, eg logs placed across the stream and supporting carbonaceous vegetative material such as fallen nikau, ti kouka and ponga leaves, dried honeysuckle vine, and tied bundles of harakeke leaves.

Suitable native species of ground cover available wild nearby include:

  • Carex lambertiana (already present on the floodplain of El Riachuelo)
  • Basket grass (already present on the floodplain of El Riachuelo)
  • Pteris tremula (already present on the floodplain of El Riachuelo)
  • Carex geminata
  • Carex lambertiana, dissita and uncinata (we noted C. uncinata dying off during the drought in canopy margins of Gahnia Grove and Tanekaha Ridge, so it is likely suitable for this wetter area)
  • Haloragis erecta (shrubby toatoa)
  • Senecio eslerii ("Esler's weed" ie Hairy Legs groundsel)
  • Solanum opacum (Dark nightshade)
  • Alternanthera nahui (Nahui)
  • Hydrocotyle moschata (Hairy pennywort)
  • Microlaena stipoides (Weeping grass)
  • Lobelia anceps

All except Nahui are among species already present in other parts of the Gahnia Grove Trial site. Nahui is present as wild material sourced in the neighbourhood and planted in the Trial site (Arena kikuyu margin)

Gahnia xanthocarpa is already present in the canopied margins of the wet area - water tolerance unknown

Gonocarpus incana, Lepidosperme australis and Schoenus tendo are abundant in the kauri community of Tanekaha Ridge to the South - water tolerance unknown.

[UPDATE A first search was made for a plantable site, from the head of the stream to the lower end of its exposed flood plain, looking for a site to plant a single Carex geminata plant (descendent of Kaipatiki Creek-ecosourced in 1997, about to be dug out from a residential lawn). The soil was porous but contained dense fibrous tree roots throughout, that would have been broken by digging even with a trowel, jeopardising the health of the trees. The C. Geminata was placed in the edge of the stream itself, stabilized with some loose sandy material from the stream bed. It seems sowing seed of fast-growing herbs, and encouraging the regrowth of foliage on the palmgrass, will be necessary to restore ground cover until tree seeds germinate and grow big enough, or the thin low canopy of the existing trees increases and becomes dense enough, to shade the ground.]

The rich fine soil will remain moist while rains continue. Seedlings will undoubtedly arise of the surrounding tree species, ie mapou, mahoe, nikau, putaputaweta, porokaiwhiri, karamu, hangehange and kohuhu, and sporelings of the quick-growing shaking brake (Pteris tremula) and ponga (Cyathea dealbata). Mamaku (Cyathea medullaris) might find sufficient moisture here.

Ongoing selective weeding will protect this regeneration, but additional ground cover is likely to be needed in the short-term to prevent dessication in dry seasons causing further damage to already-drought damaged mature putaputaweta in and beside the stream.

Some soil-stability and ground cover is provided by the bases of the large palmgrass which were suppressed individually by crushing and compacting their leaves onto their bases. These retained bases stand about 30-40cm high and will be used to retain logs, brush and other vegetative material in an effort to prevent erosion by future flooding, and trapping any flood debris to retain moisture for the revegetation.

If needed, low shade tents will be formed of bamboo (growing nearby, under canopy on Pohutukawa Bank), brush, harakeke and ti kouka leaves, decaying honeysuckle etc, allowing varying levels of light for wild and planted seedlings.

Following the Trial Methodology's standard practice for weed control, further reduction of the massed palmgrass, and ongoing suppression of the large plants with retained bases, will be ongoing as ground cover and shade are established, the focus being on the release of existing native vegetation large enough to replace the palmgrass in these functions before the next dry season. This, as always, is a complex assessment based on the expected survival and growth rate of mature and juvenile plants, and of observed or anticipated seedlings and sporelings, in the months following any instance of weed reduction. This assessment has to be combined with the expected rate of growth or reproduction of the weed concerned.

Fortunately we have found the foliage of Palmgrass easy to reduce in a quick operation, and the stumps to weaken and become uprootable if heavily mulched with their own or other plant material.

The seeds are on long slim culms that slip easily out of the plant, and can be piled and heavily covered with plant material to prevent germination. This can be done throughout the infestation at present, and in the future by cutting the flower stalks as they emerge to prevent the development of seed.

Scattered palmgrass plants outside the mass infestation are being uprooted or suppressed (depending on size) as encountered.

הועלה ב-יולי 21, 2020 11:39 אחה"צ על ידי kaipatiki_naturewatch kaipatiki_naturewatch | תגובה 1 | הוספת תגובה

יולי 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.

הועלה ב-יולי 23, 2020 03:23 לפנה"צ על ידי kaipatiki_naturewatch kaipatiki_naturewatch | 0 תגובות | הוספת תגובה