Relations between conservationists wanting to reduce the introduction and spread of invasive plants, on the one hand, and advocates of horticulture, on the other, have not always been smooth. But a workshop held during the July Hawai`i Conservation Alliance’s annual conservation conference suggests the two groups have staked out common ground.
Nearly 40 percent of the invasive plant species now plaguing Hawai`i are ornamentals that were introduced and spread by the horticultural trade (including botanical gardens, garden clubs, exotic plant collectors, and the landscape industry). In 2004, in an effort to minimize future harm from this source, scientists at the University of Hawai`i at Manoa and the U.S. Department of Agriculture’s Forest Service adapted a risk assessment protocol used by New Zealand to evaluate the invasive potential of plants in the nursery trade in Hawai`i. When the resulting Hawai`i Pacific Weed Risk Assessment was rolled out, representatives of the state’s landscape industry were skeptical.
At the July conference, organized by Christoph Kueffer of UH-Manoa, Chris Dacus and Boyd Ready of the Hawai`i Chapter of the American Society of Landscape Architects and the Landscape Industry Council of Hawai`i noted that the risk assessment failed to balance costs and benefits, describing it as a blunt tool at best. The scores given to plants assessed did not always reflect the degree of invasiveness, they said, while predictions of a given plant’s invasive potential were not always correct. The rate of “false positives” – predicting a plant to be invasive when it was not – was about 15 percent, they noted. Still, they agreed that the WRA provided an objective evaluation of plants and was better than having to deal with multiple lists of undesirable species posted on various websites, which provided uncertain guidance both to the public and the industry.
Dacus described initiatives of the Hawai`i Chapter of ASLA to provide guidance for its members in addressing invasive species issues. Working with Christy Martin of the Coordinating Group on Alien Pest Species, the Kaua`i Landscape Industry Council and the O`ahu Nursery Growers Association have identified lists of seven and 12 plants, respectively, that they recommend not be sold because of their invasive qualities. Building on that early initiative, HASLA assembled a statewide committee of representatives from all facets of the industry to review the complete list of 168 plants identified by the Weed Risk Assessment as potentially invasive in Hawai`i. Their objective was to evaluate both risks and benefits of these plants to the industry and to develop a consensus recommendation for their use. Planting options were expanded to reflect the complexity of the issue. They noted that some species, such as seashore paspalum (Paspalum vaginaum) fill a specific need for which there is high demand and no known alternatives, whereas others, such as the Australian treefern (Cyathea cooperi), could be replaced with slower growing alternatives. Unlike newly introduced species, those already widespread in Hawai`i may be little affected by industry initiatives. HASLA’s planting recommendations include “do not plant,” “use an alternative” and “avoid near sensitive locations” as well as “continue to plant” and “seek more information and industry input.” Eventually, Dacus said, the HASLA committee recommended placing 122 species on the “do not plant” list, that the industry continue to plant 22 species, and that it seek additional industry input on 25.
An industry survey done in 2007, Dacus said, revealed strong support for the planting guidelines and for reduction in use of invasive species among industry professionals. Next steps, he said, include seeking assistance in defining environmentally sensitive areas to avoid for species that will continue to be planted; reviewing and updating recommendations based on new risk assessments, increasing the use of native plants by horticulturalists; and investigating the implementation of an agreement similar to the National Pest Plant Accord developed in New Zealand between the horticultural industry and state agencies charged with management of invasive species.
— Julie S. Denslow
Volume 19, Number 4 October 2008
Leave a Reply