Sometimes species have been introduced to New Zealand with no other purpose than to add a bit of variety and colour, to improve on nature herself.
In New Zealand, two such species are heather and the rainbow lorikeet, and in both cases what seemed like a colourfully good idea has gone badly wrong. With heather, hopes are now high that the infestation can be controlled and managed via biocontrol, though eradication is unlikely. For the rainbow lorikeet, control is still focused on eradication of wild populations, before the blue-headed parrot becomes established and unseats native bird species.
Heather now covers a large section
of Tongariro National Park
Between 1912 and the early 1920s, a warden in New Zealand’s first national park, Tongariro, decided to create some grouse hunting habitat. Pink flowered heather, Calluna vulgaris, had already been introduced to New Zealand but he took it further, importing seed from Britain, Ireland and France and liberally sprinkling it through western parts of the then tussock land in the park.
Heather can still be found in a number of locations throughout New Zealand, and began to be considered a pest weed species in the 1960s, but the only substantial infestation is in the central North Island, in Tongariro National Park. Ironically, the grouse never established.
A Great Competitor
The problem with heather is that it can out-compete the vegetation it invades, causing significant biomass losses of indigenous plants and threats to indigenous biodiversity.
Although heather has potential to cause major problems in other parts of the country, to date it is only in the Central North Island that is a serious ecological concern. It spreads at rates of up to seven kilometres a year along roads, through seeds being spread by road machinery, bee keepers’ trucks and, possibly, people picking the much-admired blooms. Ongoing invasion within the national park and far beyond its boundary is turning red tussock lands into heathland.
Heather’s rapid rate of spread means it is an especially difficult weed to manage. Hand pulling and grubbing plants has limited effectiveness and grazing, fertilising and fire are inappropriate in a national park. Herbicides have proved effective but their repeated use is both undesirable and prohibitively expensive except for very limited areas at the edge of infestations. Of necessity, efforts have been targeted to key conservation areas; in others the heather is left to grow.
So hopes are quietly high that an introduced European heather-specific beetle (Lochmaea suturalis) will put ecological constraints on the Tongariro heather problem, even if it will not eliminate the plant. Partial browsing by beetle larvae and adults leads to plant death by evapotranspiration. Being heather-specific, the beetle poses no threat to indigenous plants. (Ironically, back in its Scottish home the tables are turned – there heather is at risk and the naturally occurring beetle is the pest.)
Following trials with beetles imported into quarantine, it was deliberately released in 17 selected areas in and around Tongariro National Park between 1996 and 1999. Some releases were on sites of previous vegetation monitoring, while others had new monitoring established. Annual monitoring in 1999 and 2000 has confirmed that the beetle has established in at least one site and that a dense patch of heather is now dead or dying. No native plants were affected, (unlike when herbicides are used) but the Department of Conservation will continue to monitor the site.
The colourful blue-headed parrot, Trichoglossus haematodus, was brought to New Zealand from Australia as a captive cage bird. Since 1984 it has been illegal to import the bird, but they are still bred and sold. Deliberate and illegal releases began around Auckland city in about 1992 when a breeder sought to add some ‘colour’ to New Zealand’s bush.
The problem is, the birds’ biology overlaps with that of a number of indigenous species. Rainbow lorikeets are honeyeaters which puts them in direct competition for the food of native tuis, bellbirds and wood pigeons. And they nest in tree cavities, which puts them in direct competition with other native birds - kakariki, kaka and hihi.
Unfortunately the breeder’s efforts were successful and rainbow lorikeet are established in the wild, posing a serious risk to both indigenous fauna and horticultural crops. Concerns are held for native bird populations on nearby island conservation refuges.
An Unwanted Organism
The good news is eradication of wild populations is considered feasible, though it will take at least three years. Two major considerations in planning and implementing the eradication have been:
- The need for public support and cooperation (coloured by the general perception of the bird as a harmless, pretty family pet); and
- The need to regulate the sale and movement of the birds, and educate people about the risk wild animals pose.
To achieve this it has been declared an "unwanted organism" under the Biosecurity Act 1993.
Public Support Needed
Public support is essential for the success of the programme, and is now high. DOC depends on public information to identify wild populations, and to gain access to private property without having to resort to the powers of the Biosecurity Act.
A project co-ordinator has been appointed. His role includes:
- Maintaining a database of sighting and recovery records, needs for revisiting sites;
- Co-ordinating a public awareness programme; and
- Liaising with local bodies and commercial breeders.