Test: Final Report Section 3 of 4: 2.7 Tradescantia to "following areas"

2:7 Tradescantia

Initial survey of Tradescantia in the Trial site started, after a week of considerable rain, in March 2019. The first area surveyed in depth was the roadside bank in Zones Ca to Da, where a small exploratory removal had been done in Oct 2018, and some photos included our RENH funding application.

Here in 1997 both the roadside and the “lower level” held little but a few juvenile ti kouka and dense kikuyu.
The kikuyu was mown at the roadside and uncontrolled beyond. The roadside kikuyu was sprayed prior to the planting, and all kikuyu throughout both roadside and lower level was eventually deeply mulched by volunteers with woodchips. In March 1998 the roadside was densely planted by about 100 community volunteers, with ecosourced native tree seedlings purchased by North Shore City council. In Zones Ca-Da, the planting extended about 6m from the roadside, sloping downhill.

The lower level behind was never successfully planted.

Hundreds of metres of woodchips were donated directly to the volunteer restoration project, with Council approval, by a local treecare company. This was the first use by North Shore City Council of wood chips as mulch, as woodchips had been considered to transmit weed invasion. Technical advisors and observers were unanimous in their commendation of the results of the tree planting, and no new or increased weed invasion was observed.

NSCC had until then been importing commercial bark mulch from the Waikato, at great cost. The bark mulch, coarse and smooth, often failed to aggregate or decompose before being rapidly lost from its intended site.

In 2019, as in 1999, Kaipatiki Rd was wide and busy, guttered and drained, and bordered by an informal footpath about a metre wide, of recently-mown mixed exotic grasses.

Roadside Trees
The roadside margin of the planted canopy was dense enough in places to discourage the entry of passing pedestrians, the foliage of the closely planted trees occlusive from ground to canopy in some places. Gaps in this roadside canopy margin sheltered a few juvenile natives (mapou, ti kouka, Coprosma, mahoe, mamangi), probably wild, and several small invasive trees and vines (Tree privet, woolly nightshade, Elaeagnus, honeysuckle, moth plant).

There was dense, deep ground cover by Tradescantia throughout the roadside planting in Zones Ca-Da, ending at Zone BdKRd/ KRL, near the entrance to the well-used walkway connecting Glenfield College and Kaipatiki Rd to the Witheford Dr/Bayview neighbourhood.
[In ZoneBdKRd the plantable space was, and remains, limited to a steep bank 1-3m wide, above 20m of 2mW path entry almost parallel to the road. This part of the 1998 native planting, bounded by foot traffic both above and below, holds diverse trees and shrubs and ferns, perhaps all now wild, the taller trees often leaning over the path so being pruned or felled, and those nearest the path entry appearing stunted, presumably by soil compaction, lack of canopy and ground cover. Several juvenile wattle, woolly nightshade, Elaeagnus and blackberry were controlled among these trees. The roadside lower branches of Coprosma, mapou and mahoe obstruct recreational walkers and access to cars parking daily opposite the College, so are prone to damage. Pruning back to about 1.2m from the road successfully avoided further damage to the trees and increased the density of roadside foliage].

Lower level
About 6m below the roadside, the sloping bank ended in a flat “Lower level”, several metres wide and ending at the top of a steep bank. This level was similarly covered in dense Tradescantia.

There were no trees or understorey on this lower level below the roadside planting, except a single vigorous but juvenile nikau, and a large old multi-trunked ti kouka, deep in ti kouka leaf litter. This stand was about 10m-15m H with sharply leaning and bent trunks, of which one had recently fallen, one piece several metres long remaining for months high in a group of trees at the nearby path edge.

Steep bank
A steep clay bank below the “Lower level” held moderately dense wild native trees (rawirinui, mahoe, rewarewa, ti kouka, mapou, ponga, wheki, a single live tanekaha and another now dead) and understorey (kiekie, coprosma, kawakawa, pate, ferns), several woolly nightshade over 5mH and several clumps of Kahili ginger. This steep bank was less densely covered in Tradescantia than the roadside or lower level; bare clay was visible among root buttresses and around a decaying uprooted tree base with fallen trunk and branches up to 2mD (observed already long-decaying in 1997).

Flat Streambank
At the bottom of the steep bank was a flat sedimentary sandstone streambank, canopied directly by several tall close wheki, and more distantly by taller canopy trees on the surrounding banks. The streambank was densely covered in Tradescantia, several Kahili ginger stands, a few scattered juvenile treeferns, deep piles of fallen fronds around the wheki.

A stand of Palmgrass (Setaria palmifolia) was easily broken down or uprooted, and suppressed with wheki fronds. There was some regrowth by February 2020.

The ginger was suppressed by partial breaking and bending down of all stems, covering them deeply with about 1m3 of Tradescantia. This trial technique proved simple and effective. Several months later the Tradescantia was removed, to find the ginger roots had rotted, and several large masses of otherwise-healthy and viable tubers were easily uplifted and removed to the roadside. A smaller amount of tubers remains, and would be likely to respond to a repeat intervention, but would need more interventions and monitoring in the current absence of Tradescantia to suppress stems and assist rotting.

The streambank edge held the same density and depth of Tradescantia, but here the Tradescantia hid young ferns, mostly Pteris tremula and Deparia, which grew vigorously after release.

Sporelings of treeferns are developing on the flat bank beneath wheki. A kiekie forms a wall about 2m H x 6m across one end of the streambank, descends the bank to the water, and climbs several metres up the steep bank and further up trees.
A group of young ferns in its shelter flourished on release form Tradescantia, and native seedlings incl. kanono emerged in Spring. The development of all these, and possibly their survival, has now been restricted by drought. There were signs of recovery among them after light rain in March.

Canopy
The trees on the roadside and on the steep bank, and three tall trees nearby, (a radiata pine to the NE, and a tanekaha and tree privet on the opposite side of the stream), all contributed to the thin and translucent partial canopy of the lower level, steep bank and streambank. A substantial proportion of this fragile canopy was, and is, provided by a single Tree privet c.10mH, leaning over the stream and apparently outcompeting an adjacent mahoe, the latter of similar height but with only a few short branches and scant foliage.

In March 2019 all the above areas were covered from roadside to streambed in deep dense Tradescantia.

The trial began with:

• Assessment of canopy (broken in places, mostly thin and somewhat translucent, of mahoe, ti kouka, pate and treeferns; dependent on several woolly nightshade and the large tree privet)
• exploration of dense deep Tradescantia for seedlings and sporelings (no seedlings; many Lastreopsis on the steep bank above the stream, to 30cmH and completely hidden under the Tradescantia),
• identification of mini-sites for monitored partial Tradescantia removal (in wet areas around run-off channels around several stands of tall old ti kouka, where Tradescantia was mixed with many layers of ti kouka leaf litter)
• uprooting of Tradescantia along a strip of ground about 80cm wide x 5m L on the lower level, placing the loose material at the outer edge of roadside canopy to suppress kikuyu, Paspalum, Yorkshire fog and Cynodon dactylon, retaining moisture and supporting revegetation during its decomposition.
• removal to the roadside of a pile of 8-10 recently dumped car tyres from under one mahoe, and from the wider area two wooden pallets, some iron pots, and a few pieces of timber and plastic refuse, most previously hidden by the Tradescantia under the roadside trees.

Roadside bank - soil moisture deficit and drought stress

A day or so after these activities on the roadside bank, intense sunlight returned, penetrating the light canopy and rapidly drying any spots bared by removal of Tradescantia or refuse. Where the tyres and Tradescantia had been removed, some mahoe leaves drooped (on the canopied side of the tree, not the sun-exposed side; perhaps because surface roots on the exposed side were already adapted to dry soil).

The removed Tradescantia was redistributed to cover the areas exposed by rubbish or Tradescantia removal. After about 10 days and a little more light rain, the affected mahoe leaves appeared normal.

Over the following week additional Tradescantia was brought from the streambed and applied as mulch to the recently bared areas, supplemented by harakeke prunings found nearby.

Among the root buttresses of a mature karo 1-2m from the kerb, loose dust could be penetrated with a finger to a depth of 1cm.

Closer inspection of the soil surface showed tiny white mahoe rootlets in the soil beneath the Tradescantia, exposed anywhere Tradescantia was removed.

We speculated that the soil moisture deficit had induced mahoe roots to emerge or increase at the surface to access moisture from dew and intermittent light rainfall retained by the Tradescantia.

Some observations indicating drought stress among the roadside trees after removal of some refuse and small areas of the previously deep dense Tradescantia.

After these removals and subsequent observation of drought stress, as much Tradescantia as possible was carried up the bank from the streamside to mulch all the roadside trees as deeply as possible.

Thereafter, Tradescantia removal was limited to the following areas:

Posted on August 26, 2021 10:06 PM by kaipatiki_naturewatch