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New research rings biosecurity alarm bells

New research rings biosecurity alarm bells

New research into three popular garden plants has raised serious concerns about their potential to invade and take over natural ecosystems.

The three species researched were agapanthus (Agapanthus praecox subspecies orientalis and praecox and their hybrids and cultivars), phoenix palm (Phoenix canariensis) and English ivy (Hedera helix subspecies helix and cultivars). The study looked at the distances plants could spread unassisted, the range of habitats they were capable of invading and what impacts they were having on parkland and other natural areas.

All three species were found to be invasive in a range of ecosystems, to spread into remote and inaccessible areas and to have significant environmental impacts on natural areas they invade.

Auckland Regional Council Biosecurity Manager Jack Craw says the research, commissioned by the ARC, confirms what was already suspected in terms of agapanthus and ivy, but that the invasive capabilities of phoenix palm comes as an unwelcome wake-up call.

"When we started looking, we found phoenix palms everywhere: half-grown palms that had self-sown into mangrove wetlands, young plants growing in thick kikuyu on the edges of farm paddocks, even seedlings growing alongside native nikau palm seedlings in dense bush," Mr Craw says.

"These plants are being spread into some of our most remote and vulnerable habitats by birds, wind and water. All three species are becoming significant weeds in natural areas." Mr Craw is urging developers and gardeners to consider replacing agapanthus, phoenix palm and English ivy with non-invasive alternatives.

Information on how to control invasive weeds, and some suggested non-invasive alternatives to replace problem weeds, is available from the ARC by phoning 09 366 2000.


Weeds in Auckland

• A previous study by Esler found that, between pre-1840 and 1985, introduced plants naturalised in Auckland City at the average rate of one species every 88 days. New plant species continue to naturalise in Auckland and wider New Zealand. The rate of naturalisation appears to be increasing, mainly due to the increased rate of new plants coming onto the garden plant market.

• New Zealand has more naturalised exotic plants (just over 2,000) than native species (around 2,000). Some are useful for primary production. Many co-exist at low levels and have minimal economic, ecological or health impacts. A small percentage have become significant weeds. Invasive species that naturalised a number of years ago, such as gorse, are generally well recognised as weeds. It may take a number of years to determine whether plants that have naturalised more recently will be invasive or not.

• There are also around 27,500 further plant species that have been introduced to New Zealand, but which have not yet naturalised (i.e.: produced viable offspring unassisted in the wild). A small proportion of these will naturalise in the future. Most will have minimal impacts, but an estimated 10-20% of plants that naturalise will become serious weeds.

• Auckland has the dubious distinction of being the weediest city in the world.

AGAPANTHUS: Agapanthus praecox subspecies orientalis and praecox, also cultivars and hybrids of these 2 subspecies.

• This includes all large agapanthus types

• Found to invade a range of habitat types, including roadside drains, low scrub, regenerating bush, forest margins, pasture, coastal and beachfront vegetation, sand dunes, coastal cliffs, rocky inland cliffs, exposed coastal areas, pastoral streams, gardens (very common, both planted and naturalised).

• Forms dense monocultures that exclude all other species: one cliff infestation at Piha was found to cover an area of over 1,000m2.

• Seeds were found to blow an average of 17.3m.

• Some of the new dwarf agapanthus cultivars do not readily set seed and can be safely planted. ARC is liaising with growers to establish which of the dwarf cultivars are safe and which are not.

• Those looking for non-invasive alternatives to agapanthus could try clivia (similar foliage to agapanthus and a range of attractive, large, colourful flowers), native rengarenga (widely available with foliage similar to agapanthus and sprays of small white flowers in summer), native coastal grasses such as pingao or spinifex (great for stabilising coastal dunes and helping conserve endangered native pingao), native toetoe grasses and gahnia (good erosion control for sunny and shady sandy inland sites) or one of the many varieties of native flax (hardy for dry sites in full sun and helps stabilise sandy or unstable sites).

IVY: Hedera helix subspecies helix * English ivy

• English Ivy was found invading all age classes of native forest, pine forests, roadsides, forest margins and gardens. Bird-spread seedlings are becoming common in many local reserves. Ivy infestations in regional parks tended to originate from past house sites.

• Infestations up to 160m2 were recorded. Ivy cover reached 100% in many places, completely excluding all other species. In some cases, mature trees had collapsed under the weight of ivy vines.

• Another common ivy type, Canary Island ivy, Hedera helix subspecies canariensis, was not found to be invasive. Although a large mature Canary Island ivy vine with masses of flowers and buds was found in the suburb of Morningside, Auckland, there has only been one record of a naturalised Canary Island ivy in New Zealand.

PHOENIX PALM: Phoenix canariensis

• Seeds are mostly spread by water, but also by birds. One naturalised palm was found growing over 1km from the nearest possible source.

• Phoenix palm was found invading a range of habitats, including coastal (phoenix is salt tolerant) and dense bush. A couple of naturalised palms were growing well in dense kikuyu grass. Small phoenix palm seedlings are virtually indistinguishable from native nikau seedlings, meaning that the full extent to which phoenix palms are spreading into forest areas may not be realised for some time.

• Landcare Research has classified phoenix palm as a 'sleeper weed' *a plant that spreads slowly and goes unnoticed until it becomes widespread.

• Phoenix palm is already recognised as being invasive in parts of Australia and America that have similar climates to New Zealand. It is invasive in creek lands in Melbourne, very common in New South Wales and has naturalised in northern Victoria and some areas of Western Australia. The California Invasive Plant Council has advised that phoenix palm will be included on their next invasive plants list, due out before the end of 2004.

• The robust, sharp spines can cause severe injuries. 21 children were admitted to Starship with phoenix injuries between 1992 and 1997. Over the same period, 8.4% of all foreign body injuries were identified as phoenix palm incidents.

• New Zealand has only one species of native palm; nikau palm (Rhopalostylis sapida), which is found nowhere else in the world.

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