Test: Final Report, Section 1 of 4

Final report on 2019/20 Trial of Site-based non-chemical weed control for ecological restoration

Many findings have already been reported, some in more detail, in earlier photo observations and/or text reports. Here we try to summarise our experience of the application of this methodology to a site during a single year of integrated ongoing survey, planning and intervention.

Some locations are named, eg Zone Ca, or ZoneCaKSS. Links to all the Trial Zones and locations, or “sub-zones”, are provided here.

This trial aimed to

1. demonstrate the effectiveness of manual weed control over time

2. help establish optimal rates of weed reduction for gradual replacement of invasive plants with native wild vegetation.

   NB Maximum effectiveness means maximum growth, density and diversity of native vegetation. Weeds are removed because they are inhibiting existing or potential native habitat. So effective weed control requires assessment of the likely or potential development of native habitat, the needs of existing or potential species in that habitat, and the minimisation of soil moisture loss, habitat disturbance, erosion, soil contamination and water pollution.

3. Assess changes since the fulltime volunteer restoration project of 1997-99, especially observable results of both intervention and non-intervention

Unless otherwise noted Observations below are limited to the defined Trial area, ie the banks below Kaipatiki Roadside, down to the stream and up the opposite bank to the forest path (“Native Plant Trail”).

Ongoing survey

The methodology’s attention to species identification throughout the trial helped preserve, at least temporarily, some existing native plants and invertebrates, and facilitated the beginnings of regeneration in some areas impacted both historically and recently by Reserve users, along the roadside, on the banks below, and along the forest path.

1:1 Plant identification

Of special interest among species identified during the Trial were some natives often either damaged accidentally, treated as weeds due to their common occurrence in cultivated land, or misidentified as exotics they closely resemble.

Following standard practice, no plant was damaged unless it had been identified as exotic. Photographs were taken, sometimes many times until diagnostic features were successfully captured in the images uploaded to iNaturalist for discussion and species ID or confirmation by experts, particularly of ferns. Visitors made some identifications of large trees. No plant material needed to be collected for ID purposes, though some known exotics, eg a fan palm seedling and an invasive grass, were collected for closer study and photography.

With this invaluable help, we learned to recognise some species new to us, eg:

• the invasive fern Cretan brake (Pteris cretica), which was removed from several streambank locations, releasing native Blechna and Deparia
• the native Dark nightshade (Solanum opacum), found both beside the path and on sun-exposed edges of the streambank, sometimes among groups of the very similar Black nightshade (S. nigrum), which is itself a benign exotic that provides ground cover, shade that nurses native seedlings, and fruit observed being eaten by birds
• several invasive palms, after discovering the banks of the Kaipatiki Stream now hold several mature Bangalow and a Chusan, numerous Phoenix and Bangalow seedlings, and an unidentified species of Fan palm seedling.
• Calystegia sepium, x silvatica, a hybrid of the native Hedge bindweed (Calystegia sepium subsp roseata) with the invasive exotic Calystegia silvatica, ie the locally common weed often referred as convulvulus. This bindweed overtook about 20m of the 1998 roadside planting of kanuka and is still common here, though less abundant in the now-canopied areas of roadside, and possibly not harming the present vegetation.
• Off-site, we discovered the uncommon native bindweed itself, (C. sepium subsp roseata), possibly planted, in Eskdale Reserve (Domain Rd raingarden), and native Coastal Morning Glory (Ipomoea cairica) wild in Eskdale Reserve, but did not find either species in the Kaipatiki Creek Trial area. [Both C. sepium subsp roseata and Ipomoea cairica appear to be suitable replacements for vine weeds in their natural role of shading and sheltering the outer margins of coastal forests. Establishment of these vigorous but locally uncommon native vines might reduce invasions not only by sun, and wind, but by weeds, refuse and people].

1:2 Habitat

Native fauna observed on the site included:

• White-faced heron, tui, N. Island fantail, Silvereye, Grey warbler, Kereru, NZ Kingfisher, White-cheeked Rosella
• NZ Glow Worm, Giant earthworm (Megascolecidae), Cave weta, Tanguru chafer, Nurseryweb spider, Green Orbweb spider, NZ Giant centipede

In contrast to 1997-99, no copper skinks were observed. One fleeting observation of movement on the ground suggested, by its size, a plague skink.

A variety of native and exotic invertebrates were observed throughout the year in all areas of the site, especially in rotting wood (standing or fallen), among dead leaves and beneath undisturbed Tradescantia. Earthworms became common above ground in winter in decomposing Tradescantia piles, and Giant earthworms (native?) were seen on the soil surface when turning Tradescantia piles and underneath discarded plastic weed bags.

We did not see any Tradescantia beetles, or the leaf damage typical of the Leaf-eating Tradescantia beetle. However, no systematic searches were made.

Wide areas of impermeable inorganic materials left in the forest, while hindering successful development of seedlings and juvenile trees, have become invertebrate habitat. During the staged gradual uplifting, and later winter removal, of large plastic weed bags from the roadside and lower streambanks, we unexpectedly exposed a young Cave weta, some centipedes, and a giant earthworm, Cover was immediately replaced with plant material, which may or may not have provided equivalent humidity and predator protection.

The removal of plastic ground cover during unrecognised extreme soil moisture deficit, followed shortly after by a return to drought, may thus have resulted in loss of invertebrate individuals or populations.

Elaeagnus berries lost in the reduction of Elaeagnus invasions would have provided much-needed bird food during the drought.

Pest and predator animals

Domestic cats were occasionally observed in the forest. Feral cats were not observed, but are present in neighbouring forests and are seldom obvious.

Reduction of Elaeagnus would have resulted in partial loss of the cat-proof habitat provided by Elaeagnus to native fauna.

Rat traps set by a volunteer were informally monitored in two locations (ZoneCaWSS, ZoneBdWRS), and several successful kills noted.

Bait and monitoring stations set by contractors were noted and avoided.
Vespula and paper wasps were rarely seen after March 2019.

1:3 Water quality and Freshwater ecology

Observations of the stream were not systematic or prolonged, and an evening visit was not made, but nonetheless we were surprised at the ongoing absence of bubbles, water splashes, or shadowy movements suggesting fish and eels.
Only one or two damselflies were observed, no wasps or bees drinking from the edges of the stream.

This may be partly attributable to water temperature, which was not tested. A single heavy rain event was observed during the winter, in the Trial area, and the flood level in that event was modest, causing little disturbance of streambanks, compared with levels seen regularly in 1997-1999.

During the heavy rain event of 1 April 2019 we observed what the (apparently routine*) overflow of raw sewage into the stream from the many sewage manholes along the streambank. We were unable to obtain information from Council or Watercare on the water quality test results that are done from a weir a few hundred metres downstream of the Trial site.

/*Local residents report that the distinctive smell occurs regularly after rain and can be smelled from surrounding streets

Untreated stormwater is still piped directly into the stream from private properties and roading. As in 1997, this results in the stream becoming whitish-grey after first-flush rainfalls, which wash heavy metals and other pollutants directly into the stream.

We speculate that following extreme drought, the low level of water in the stream will result in even greater concentration of the usual post-rain, or “first flush”, stormwater pollution. Such concentration of sewage and stormwater pollution in post-drought rain events may already occurred prior to March 2019.

Outside of heavy rain events, stream water was clear in all seasons in the areas accessed during the Trial, but not closely observed further up or downstream inaccessible due to either dense native revegetation, eroded banks and fallen trees, or dense infestations of crack willow and Japanese honeysuckle.

“Willow Crossing” area was, in 1997-99 a slow-flowing area, unshaded on the roadside bank and prone to algal blooms in summer. This area was not observed during 2019-20, as the 20 year old planted trees and new vine invasions now hide the stream and prevent easy access from the road. However, this suggests the dense vegetation is shading and cooling the stream as intended, and algal blooms may have diminished.

Shortly downstream of Willow Crossing, the streambed has, as in 1997, several metres of concrete streambed including a weir.
By chance we observed a regular scheduled visit for water quality data collection, but were unable to contact anyone with information about the results, which we are told include regular automatic monitoring of flow rates.

Stream formation
Sediment in the Trial area’s streambed did not seem (in wading) significantly deeper than in 1997-00, as we recall it. Banks appeared somewhat higher and in places unstable, with more exposed tree roots than in 1997-00, suggesting scouring. There are still undercuts/overhangs for kokopu habitat, but fewer submerged logs and sticks in the streambed, which (excluding periods of drought) probably carries a larger volume of both runoff and piped stormwater than 20 years ago, and higher volumes of sewage/stormwater overflow from manholes after rain events.

As usual and desirable in such habitat, partial dams have formed from logs, water-borne debris (organic and inorganic) and sediment. The pools observed above such dams were no deeper than 30-40cmD during the 2019/20 Project year, one of prolonged extreme drought.

Large fallen and uprooted trees, eg mahoe and treeferns, hang over parts of the stream, often creating overhangs in the streambank. Such treefalls, in otherwise-intact streamside forest, are part of the natural process of stream formation. The resulting dams and eroding banks create wider, slow-flowing areas and sediment sandstone islets, (eventually covered in ferns, carex, and juvenile trees) contributing in the long term to the meandering of the stream, which in general still follows its 1997-00 path. The overhangs provide habitat for kokopu, which inhabited this stream in 1997-99.

Refuse and litter in the streambed
Other than solid waste, toilet pater and plastic refuse left by the sewage overflow of April 1st, refuse in the streambed was minimal. Most of it appeared to be long-standing, including a foam mattress, car tyre, plastic containers, and a semi-buried section of synthetic carpet.

In contrast with the truckloads of refuse and several car bodies removed from the streambed and near banks in 1997-99, we observed only one or two items of larger flood-borne refuse such as telegraph poles, water tanks, construction materials, furniture and vehicle parts.

Litter, especially plastic drink bottles, was also much less common in the streambed. Though there continues to be roadside litter and frequent illegal dumping, including household lots, butchered animals and bulk containers of hazardous and flammable chemicals, these are largely retained near the roadside by the density of the planted trees.

The stormwater drains in the road may now have smaller openings, filtering larger pieces of debris before stormwater enters the stream. We suggested this in 1999, and were told at the time that that would block the drains with rubbish, and that the collection of rubbish from stormwater drains would be an “upgrade in service” prohibited by cost. We don’t know if this service has since been implemented, or if there are just fewer plastic drink bottles in the gutter and stream because of changed habits among motorists and pedestrians.

1:4 Inorganic refuse in roadside and forest

Dumpings
Following the 4x20 litres of hazardous flammable chemical fluid, found, with a pair of industrial gumboots, in June 2018, and the removal of a stack of 8-10 car tyres in March 2019, dumped refuse and litter at the roadside was ongoing until we completed a pigtail cordon along the roadside. Dumpings reported to council for pick-up included furniture, appliances, timber, plastic sheeting, road signage (probably discarded by vandals when they tired of it) and a household lot of mattresses.

Waterborne refuse
A substantial collection of litter, mostly drink containers, was found trapped by Tradescantia in the rough concrete-and-rock culvert channeling stormwater to the stream from the roadside and playing fields across the road (Zone EaKRS/EbKRS).

Equipment remaining from prior activities
During Tradescantia removal in the forest, old broken plastic pest-control tunnels were found in two locations among dense understorey and with tree roots growing through them. The tunnels were able to be detached and removed, and the nikau roots placed back in contact with moist soil and covered with leaf litter.

Black plastic kleensaks and mesh weed bags found under Tradescantia on lower level banks and streamsides were left in place until winter, to avoid breaking rootlets and desiccating habitat. However, with unanticipated and increasing soil moisture deficit and drought, their removal undoubtedly contributed to the later drought-stress and plant loss.

Posted on August 26, 2021 10:08 PM by kaipatiki_naturewatch