Granto

Scope of work for the post-quake landscape remediation involved the maintenance and management of 7.6 hectares of planted Port Hills Red Zone sites, in the rim locations of Governors Bay, Lyttelton and the hill suburbs through from Sumner to Cashmere.

The challenge for Red Tree was to establish native plantings and binding ground covers on tough clay substrates, gradients and North-facing aspects to revegetate and stabilise the land.

Establishing native plants were forced to compete with invasive weed infestations of Fat Hen, Californian Thistle and Mallow, utilising organic weed control in high density residential zoning.

Nature abhors a vacuum and in ecological terms that translates to, “ bare earth will not be tolerated”. In short order, Mother Nature covers exposed earth, as without protecting vegetation the earth surface is highly susceptible to wind and water erosion. Downstream sedimentation is the consequence!

Red Tree utilized a clover plant companion technique; attractive to insects and bees, this versatile legume, with its distinctive flowers and cheerful foliage, belies a mass of rubbery roots that work to fix nitrogen into the soil as it creates a tenacious mat to bind the earth.

Clover species are numerous and by introducing the variety of clover containing the most appropriate attributes to the disturbed urban hillside sites, we were effectively able to suppress the existing bank of less helpful weeds and in conjunction with jute matting, quickly stabilize the cut faces.

In Nature nothing is wasted, everything is recycled. Red Tree Plant Technicians then hand release the natives, cutting out weeds around the stems and using the recycled biomass as a mulch around the plants. Topping using bush cutters was employed to prevent seed dispersal. On tough sites, it is essential that valuable biomass is recycled and able to enhance soil structure.

Through observing challenging site conditions and mainstream methodologies, Red Tree began conducting research in direct-seeding natives and compost-based revegetation technologies. With the intent to improve outcomes in harsh environments, the Enviroblanket® development was underway.

In support of the new technology’s potential, LINZ awarded an entire Red Zone site for Red Tree to trial the Enviroblanket®. Applied alongside traditional planting for comparison, the direct-seeding technology proved to be extremely successful.

NCTIR (North Canterbury Transport Infrastructure Recovery) was an alliance established to tackle the recovery efforts of both the road and surrounding areas.

An army of people, trucks, and diggers created multiple permanent stockpiles and engineered batters using the slip material removed from significant slips within the transport corridor. These stockpiles and batters were devoid of vegetation, topsoil, and nutrients, presenting a challenge to re-establish flora onto these degraded clay and mineral substrates.

Eco-sourcing plants to add aesthetic value to the newly established safe stopping areas and to stabilise engineered stockpiles and batters was a challenge due to the short timeframes and large volumes required.

Red Tree specializes in using eco-sourced native seed in post-natural disaster ecological restoration projects and was engaged to undertake a combination of traditional planting and Enviroblanket® applications along the damaged coastline.

A prescriptive coastal Enviroblanket® was designed to withstand the harsh environmental conditions presented in Kaikōura and to facilitate remediation of degraded substrates.

In 2018, Red Tree, in collaboration with other local nurseries, collected eco-sourced native tree and shrub seed within the Kaikōura ecological district. Invasive pest plant management was then undertaken in 2019 to prepare sites for planting and direct seeding.

In 2020, Red Tree traditionally planted more than 55,000 native plants and pneumatically installed approximately 4 hectares of Enviroblanket® across multiple sites within the corridor. In order to remediate a particular inaccessible slip site, Red Tree also developed and applied an aerial Enviroblanket® via helicopter.

The first commercial large scale Enviroblanket®, effectively an on-site nursery; could it be done?

Native direct seeded Enviroblanket® technology, developed by Red Tree Environmental Solutions (Red Tree), is essentially disruptive in that it bypasses the nursery system, interacting directly with disturbed substrates in a responsive time frame. Letting nature lead and assisting with biomimicry and self-design principles, Red Tree aims to replicate the life-giving function of the forest floor.

An undisturbed soil profile provides established networks of root systems, microorganisms, and mycorrhizal creating nutrient pathways, aeration, and drainage. Once the natural soil structure is disturbed and modified, there is a significant loss of soil ecology. This disturbance and compaction of engineered soils produced a major challenge to seed germination and healthy plant growth on this site.

Exposed to the elements, this large and open area is continually subjected to environmental extremes such as high wind velocity, sun exposure in the summer, and sinking cold during the winter with the attrition of browsing pest animals such as rabbits and hares.

Adjacent to a traditionally planted area, a one hectare dry forest Enviroblanket® was applied in August 2019 around the perimeter of the wetland basin. Nature provides direct feedback as to which species are best suited to variance within specific microclimates; species best suited to environmental conditions display higher germination rates with success being reflected in strong growth and plant resilience. Biomimicry and self-design capacity that the Enviroblanket® provides, gives nature the best opportunity to select species best suited to adapt and thrive in local environments.

During site preparation, mechanical ripping was undertaken to address compaction, improve poor soil structure and drainage. Biological additives were applied to the Enviroblanket® post-application to assist biogeochemistry health. Microorganisms and fungal networks rebuild microbial activity in the soil which in turn creates a symbiotic relationship between plant communities, builds resilience, and improves growth.

As this site is widely exposed to the elements, Red Tree utilised a fast-growing native nurse crop to provide protection and cover during the first year of establishment for the slower growing natives to emerge through.

Mitigation of pest browsing effects was undertaken in conjunction with Excell Biosecurity, implementing pest reduction controls and perimeter fencing in the most challenged areas.

Loess is comprised of platelets which carry a negative charge facilitating ion exchange once saturated and is therefore extremely partial to erosion. During precipitation onto the Sumner Road catchment, high velocity sheet flow was running down slopes above the vertical cuts and eroding the loess faces.

Sumner Road above LPC was still under construction after being closed following the Christchurch earthquake sequence. Being directly above the port operations and below the new road construction, this site was extremely high profile.

Coordination and communication between these two large civil construction projects was a challenge that required high levels of compliance and health and safety. Once windows of ingress were coordinated, gaining access to the steep slopes above the vertical cuts was also a challenge. Rope access teams were required to move across the slopes and work on the eroding cut faces.

A series of Enviroberm®’s and an Enviroblanket®, delivered via Canterbury Woodchip’s industrial high tech pneumatic applicator, was considered as an effective solution for the vertical cut faces and steep gradients above.

Trapezoidal Enviroberm®’s with dimensions 300mm high and 600mm wide were installed perpendicular to the gradient on the steep slopes above the eroding loess cut face. Enviroberm®’s bisected the slopes; constructed at intervals to interrupt sheet flow and facilitate infiltration. Rilling etched into the landscape from previous water flow indicated how best to work with the hydrology of the slope.

To remediate continued loess erosion, Red Tree Rope Access Teams securely pinned a dense three-dimensional reinforcement mat onto a portion of the vertical cut and managed the pneumatically applied Enviroblanket® onto the interface. Specific species of clover and drought tolerant grasses were selected and seeded over the Enviroblanket® to stabilise and vegetate the cut face.

The landscape design and planting required functionality and high amenity value.

As the project backs onto native bush, this site is a hotspot for goats, deer, rabbits, and hares. The pests meandering down the valley and browsing the plantings has been a significant challenge in this project, with some of the bigger tree species becoming victimised by young stags shedding their velvet.

Moved by the sculptural ribbon like topography, Red Tree’s in-house Landscape Designer allowed the plantings to accentuate the contour of the land and water course, creating corridors of visual passage across the plantings. Kowhai, ribbonwoods, lancewoods, mountain flax, pittosporum, carex virgata, and silver tussocks were all part of the plant palette.

In consultation during the conceptual design phase, Red Tree’s horticultural team anticipated the presence of pest plants and recommended ideal plant spacing and full mulch coverage at ~75 mm depth. For ease of mind, our clients engaged with our three year maintenance and monitoring package, which allows Red Tree to guarantee 95% establishment success and protection of their investment.

Plant losses due to pest browsing were detected early in the maintenance phase. Pest management was then undertaken and the unharmed plants were caged, with replacement plants being installed the following planting season.