Invasive Plants

On 5th January 2004, Heta, a Category 5 tropical cyclone, struck Niue and widely devastated its N to NW exposed coastlines from Uluvehi to Alofi.

This paper is a report on a collection of plants made during an 11-month stay in Samoa, from August to November 1929, and from June 1931 to January 1932, and on other Samoan collections of plants in Bernice.

As our global economy grows and the boundaries between nations shrink, we face new social, environmental, and economic challenges.

The papers in this volume were, with a few exceptions, presented at the third Island Invasives conference, held in Dundee, Scotland in July 2017. The papers demonstrate up-scaling in several aspects of eradication operations – not least in ambition, land area, operational size, global reach and of course financial cost. In the space of a few decades, the size of islands treated for invasive species has increased by five orders of magnitude – from a few hectares to over 100,000 ha or 1,000 km2.

Biological control of introduced weeds in the 22 Pacific island countries and territories (PICTs) began in 1911, with the lantana seed-feeding fly introduced into Fiji and New Caledonia from Hawaii. To date, a total of 62 agents have been deliberately introduced into the PICTs to control 21 weed species in 17 countries. A further two agents have spread naturally into the region. The general impact of the 36 biocontrol agents now established in the PICTs ranges from none to complete control of their target weed(s).

Invasive weeds are one of the most serious threats to biodiversity and sustainable development in the Pacific region. Biocontrol is likely to be the only feasible way of managing many widespread weeds, but is not always appropriate or successful. With so many weed species to tackle and inevitably limited resources, prioritising where to direct control efforts most effectively is of key importance. Landcare Research recently developed a framework for the Australian government that allows the best and worst weed targets for biocontrol to be identified.

Native plants and animals can rapidly become superabundant and dominate ecosystems, leading to claims that native species are no less likely than alien species to cause environmental damage.

Biological control of weeds in Vanuatu began in 1935, with the introduction of the tinged Teleonemia scrupulosa to control Lantana camara. To date, nine biological control agents have been intentionally introduced to control eight weed species. Seven of these agents have established on their respective hosts while an eighth, Zygogramma bicolorata, an agent for Parthenium hysterophorus has only recently been released and establishment is unlikely.

The main outcome of the project was the control or significant reduction of chromolaena in most provinces of PNG. Areas that were once monostands of chromolaena have been converted back into subsistence farms, and plantations in which chromolaena was the main understorey species are now clear of the weed. This outcome was the result of the primary outputs of the project: (a) knowledge of the extent of the chromolaena problem and its impact of the livelihoods of smallholders, (b) an understanding of effective biocontrol agents and (c) significant capacity built in biocontrol of weeds.