Source: Environment Canterbury Regional Council
Last year, we introduced a long-term action plan and willow management strategy to focus our existing efforts stamping out the small population of invasive crack willow on the lake’s edge, before they take root and negatively impact the overall condition of the catchment.
While some non-invasive willow varieties are used for erosion and sediment control, other species like crack willow can become invasive and outcompete native species.
Crack willow can spread quickly—even the smallest of stem fragments can travel downstream and take root.
Once established, their dense canopy shades out low-lying natives provides habitat for pests like possums and rats, and alters water flow.
Crack willow can displace native species and alter waterways
Starting at the top of Scamander Stream, we’re targeting the problematic willows with proven techniques like the “drill and fill” method. This involves drilling downward sloping holes around the trunk of the tree and filling them with a weed control solution.
To tackle regenerating and immature willows, we use the “frilling” technique by cutting notches around the base of the tree and applying herbicide gel/paste to the cut area.
Working from the top of the waterway means a better chance of preventing any further encroachment of the willow via fragments traveling downstream.
“Scamander Wetland is a great opportunity to take a proactive approach to conservation,” says Ewan Bakker, Biodiversity Advisor.
“We have a wetland ecosystem here that’s largely intact with huge ecological, cultural and aesthetic values but with a burgeoning issue of invasive woody weeds.
“By getting control work in there early, we’re preventing invasive crack willow from dominating and outcompeting native species and thus significantly impacting the health of the wetland.”
Preserving a wetland environment
Wetlands are internationally recognised as some of Earth’s most biodiverse environments.
In Aotearoa, our wetlands support the greatest concentration of wildlife out of any other habitat in the country.
Connected to our region’s lakes, streams, rivers, and estuaries, wetlands perform many valuable functions and are crucial to the health of our environment. Acting like a natural aquatic filtration system, wetlands clean the water that flows into them. They screen out nasty contaminants, add oxygen to our freshwater, remove excess nutrients, trap sediment and soils and return nitrogen to the atmosphere.
Wetlands are also considered taonga by mana whenua as they provide habitat for a variety of indigenous plants, fish, animals, and freshwater invertebrates.
Scamander is a largely healthy and thriving wetland ecosystem that supports a diverse array of native bird and aquatic animals, including the nationally vulnerable Australian crested grebe/pūtekeke, critically threatened Australasian bittern/matuku-hūrerpo, the eel/tuna and various species small freshwater fish.
However, like all wetland environments, invasive pest plants pose a serious risk to this habitat.
“Weed control is a long-term game and it requires continued efforts to maintain the gains we’ve made in this catchment, but it’s been encouraging to see what can be achieved when we take a proactive approach to protecting biodiversity,” says Bakker.
Wetland management is an important part of the Canterbury Land and Water Regional Plan.
