The New Zealand Currant Bush is creating sterile Australian forests
In short: What began as a popular garden ornamental has transformed into an ecological nightmare. Karamu is now suffocating Australian landscapes, out-competing native giants for water and creating dense thickets so impenetrable that they can only be cleared with heavy forestry machinery.
Karamu (Coprosma robusta), originally from New Zealand, has transitioned from a backyard favorite to an invasive weed in Victoria and a noxious species in Tasmania. Its primary threat lies in its aggressive growth habit: it forms dense thickets that shade out the understorey while simultaneously starving native trees—including large wattles and gum trees—of essential water. Because its seeds can remain dormant for many years, the plant possesses a persistent ability to re-establish itself even after initial removal efforts.
The ecological damage is compounded by a biological feedback loop involving local wildlife. Birds consume Karamu berries and subsequently drop seeds across the bush, swamping native vegetation with new growth. Even more concerning is the discovery of a hybrid species; DNA testing confirmed that Karamu is breeding with its Australian cousin, the Prickly Currant Bush (Coprosma quadrifida). This hybridization suggests the potential for fertile offspring that could accelerate the spread and impact of the invasive plant across diverse habitats.
Management requires a tiered approach based on the size of the infestation. For small seedlings, hand-weeding is preferred to minimize disturbance to remnant vegetation. Medium saplings up to 1 meter are typically cut and poisoned using spot-gun applicators. For large, established trees in dense areas, experts use 'frilling'—hacking the trunk base with a machete or chainsaw to expose the cambium wood for poisoning. This method allows the dead trees to remain standing as temporary habitat while the community works toward long-term restoration.
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Sources
- Summary by Intellect · source: How Karamu is threatening Australian native plants and wildlife | Discovery | Gardening Australia
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