Source: Environment Canterbury Regional Council
Exotic and weedy pest-plants like gorse, scotch broom, lupins, and willows threaten the fragile balance of life in this catchment — reducing habitat for native fauna and providing shelter for predators.
Additionally, invasive plant life can even change the dynamic way that braided river channels move across a river plain. Dense weedy colonies growing in and along a braided river system can stabilise gravel, restricting water flow and river gravel deposit.
This restricted movement has major impacts on many of our native bird species, like the nationally endangered ngutu pare/wrybill, which rely on raised beds of bare river gravel to nest and breed.
Willows invading stable river braid
“Many of the weedy invaders we have recorded in this area are garden-variety escapees from private land in the surrounding area,” says Will Todhunter, biodiversity and biosecurity advisor.
“To understand where the pest plants are coming from, we’ve had to take a catchment-wide approach, surveying the wider landscape including the surrounding forest, wetland and alpine ecosystems.”
This work involved extensive ground and ariel surveys, which were used to inform a comprehensive map showing the weed density of the upper Waimakariri River basin.
From there, experts came together to finalise the strategy to attack problematic plant infestations to contain, or where possible, eradicate the unwanted species.
Weed interventions show progress
After just two years, promising initial gains have been made in tackling large seed sources of weeds and initiating control at new sites.
“The weed fighting game is a long-term one, meaning maintenance works will be critical over many years to keep the pest plants at bay.
“However, it’s been encouraging to see what can be accomplished when like-minded agencies, passionate community organisations and landowners come together,” said Todhunter.
Looking ahead, work is planned to further protect the Craigieburn Forest and surrounding land from the invasion of ‘homestead weeds’ like sycamore, holly, cotoneaster and cherry laurel.
The upper reaches of the Waimakariri will also see some interventions, as well as Arthurs Pass National Park to fight Russel lupin and Spanish heath.
