Dry Forest EnviroblanketĀ®

Curletts Road Stormwater Detention Basin

Christchurch
2019 - Present

Backstory

Land erosion, sedimentation, and poor drainage, resulting from the impacts of the 2011 Christchurch earthquake sequence produced flooding and damage to properties adjacent to the Heathcote River. To mitigate this inundation, the Christchurch City Council Waterways and Catchment Management Team commissioned the Curletts Road Stormwater Detention Basin to provide upstream flood prevention and peak flow attenuation.

Prior to creating the detention basin, the area was pasture with the Curletts Stream running through it. In order to detain and filter water, a sizeable ~8 hectare excavation needed to be formed and landscaped accordingly.

The Challenge

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.

The Solution

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.

Outcome

Initial germination occurred in September and October of 2019. One year on in November 2020, plant establishment ranged in height from 5cm to 50cm and secondary germination was observed among wind dispersed pioneer species. Fast forward another year on in 2021, the plants range in height from 30cm to 1.8m; a stark contrast to traditionally planted natives exhibiting signs of dehydration and transplant shock.

Canopy cover in standard revegetation, growing in optimal conditions at 1.5 m spacings, will take approximately three years.  The Enviroblanket® has demonstrated at Curletts Road that this outcome can be achieved within 20 months post-installation, facilitating rapid growth and establishment.

Directly applying eco-sourced native seeds into an environment conducive to their success ignites healthy competition and builds resilience. Plants naturally grow more successfully and with greater resistance to pests and diseases in supportive and biodiverse communities. The observed increased density brought about by direct seeding supports plants to outcompete weeds therefore reducing inputs and maintenance costs.