Source: Environment Canterbury Regional Council
Rakaia Gorge is rich in native biodiversity.
Kōwhai, broadleaf, coprosma, wineberry and lancewood species make up some of the mixed hardwood vegetation – alongside the occasional taller forest species such as mataī and tōtara.
The area contains large numbers of fierce lancewood (its conservation status is naturally uncommon), as well as silver tussock grasslands and diverse shrublands containing matagouri, corokia, and porcupine shrub.
The mahi to protect these species began in 2020. Sycamore, wild cherry and cotoneaster were the initial weed targets, followed by wilding conifers.
These species threaten native vegetation by outcompeting it.
Selwyn District Council’s Andy Spanton (left) and weed control contractor Steve Frame
Drone mapping and survey
Two rounds of drone orthomosaic imagery were done in autumn 2023 and 2024 to help get a better understanding of priority weed sites and the most appropriate control methods.
This type of mapping uses special software to remove scale variations and distortion, providing a highly accurate ground picture. A trial aerial control operation was then carried out, targeting a 500 square metre patch of sycamore and around 60 large wilding conifers in steep and hard-to-access areas.
An ecological assessment was done in and around Terrace Downs earlier this year. This involved surveying 28 areas of different vegetation types to provide detailed species lists and mapping.
Five threatened plant species were found, along with threatened birds and animals including the kārearea/New Zealand falcon. It was also noted that the site is likely a habitat for reptiles, many of which are threatened.
This past year has been the largest funding and work season so-far. Just over $250,000 in total project costs has been invested, including in-kind (non-monetary) contributions.
Total investment to date is estimated at more than $794,000, including our financial contribution of about $244,000.
Land Management and Biodiversity Advisor Michelle Ingham says the area contains a unique ecosystem that’s worth protecting.
“There are a lot of threatened and at ‘at risk’ species and it’s a really intact environment. Apart from the threat of weeds, it’s in a relatively natural state.”
Michelle says the team’s hard work is paying off.
In July 2022 (left) this area was cleared of sycamore – now (right) there’s a large patē/7 finger plant growing
“Through the dead weeds, you can see the new native vegetation coming through. Contractors have also found some cool insects, so the project is helping them too.”
Future funding to fill the gaps
More funding is needed for stage two of the programme, which will target the remaining areas that have not yet had any weed control work. This will help prevent further invasion of weeds into ecologically sensitive parts.
It’s anticipated that direct weed control in stage three will be less intensive, and work will shift towards site-wide monitoring and maintenance to secure the gains made.
Selwyn District Council Environmental Team Leader, Andy Spanton, says the project represents an excellent partnership approach.
“The way agencies and gorge landowners are working together to help protect this fantastic repository of native biodiversity is pretty special.
“It’s important that this commitment by the partners continues into the future. Weed species will still be present, so they will need to be monitored and controlled when necessary.”
Michelle agrees the collaborative approach is key.
“The support and enthusiasm from the landowners and agencies involved is what’s driving this work, and its success.
“We have a ten-year vision – we ultimately want to see fewer weeds coming back, and as a result, new indigenous vegetation taking off.”
