Hawai`i spends more to control invasive plants than it does for any other group of pests. Millions of dollars a year go to control miconia alone. But the state stands to lose more than just tax dollars if no effective system is developed to control invasive species. Anyone planting anything in Hawai`i needs to be aware of the impact of that action on delicate island ecosystems. But whether that awareness should be backed up by regulation or voluntary compliance is an ongoing matter of discussion.
To have that awareness, planters need a source of reliable information. That’s the impetus behind the development of a weed risk assessment (WRA) for Hawai`i. Curt Daehler, associate professor of botany at the University of Hawai`i, developed the system from procedures in use in New Zealand and Australia.
At present, the WRA is being used to evaluate plants already in the Hawaiian market. Eventually, its sponsors – the University of Hawai`i, the U.S. Department of Agriculture’s Forest Service, and the state Department of Land and Natural Resources — hope anyone importing plants will voluntarily submit them to a WRA evaluation. The results would then be added to a master list of evaluations that would be available to the public. According to Julie Denslow of the invasive species unit of the U.S. Department of Agriculture’s Forest Service, the WRA list will be more reliable than others that have been developed over the years because it uses tangible scientific methods coupled with expert opinion.
The WRA was unveiled to Hawai`i’s horticulture industry and regulatory agencies a year ago. Teresa Trueman-Madriaga, coordinator of the Division of Forestry and Wildlife’s Urban Forestry Community, provided a forum last December for nursery owners and landscapers to get acquainted with the idea and voice their concerns.
Leland Nishek, owner of Kaua`i Nursery and Landscaping, Inc., generally supports the idea of the WRA. He says he and others who attended last year’s meeting realize “that there’s a problem and we need a way to solve it fairly for everyone concerned and to do it through cooperation and not excessive regulations.”
But a differing view was offered by Leland Miyano, a landscape designer on O`ahu. “I wonder É exactly what the WRA can accomplish so long as it relies exclusively on voluntary cooperation,” Miyano says. “I know a lot of people in this business and they like things that grow fast for fast turnover. I know a lot of people who won’t cooperate.”
Rod Randall, who oversees the WRA in Australia, also challenges the effectiveness of voluntary compliance. “It’s a tough question,” he says. “To be honest, I wouldn’t expect any screening system to work anywhere without regulation.”
As an example, Randall points to New Zealand, which tried to stop the distribution of weedy plants by nurseries through voluntary compliance. “They went to a lot of trouble and most of the industry came on board, but because of a recalcitrant minority they moved to regulation,” he says. “I doubt the situation would be any different in the U.S. and would probably be worse, considering the market size and economic forces in operation. Money first, environment second.”
The Challenge
At present, the WRA is being used to evaluate plants already in the Hawaiian market. Eventually, it is hoped anyone importing plants will voluntarily submit them for a WRA evaluation. Despite the overwhelming problem of invasive species in Hawai`i, a presumption of innocence exists when it comes to importing new plants. So long as a plant doesn’t appear on the Department of Agriculture’s (DOA) Noxious Weed List it can be legally imported. Results are sometimes disastrous. Plants with desirable qualities, such as miconia with its dramatic, colorful leaves, can turn from pretty to pest in a blink of an eye.
Seeing past those qualities that make a plant attractive to those that may make it invasive is perhaps the greatest challenge in the fight against plant pests. Making it all the more difficult is the fact that the invasive nature of these weeds isn’t apparent overnight, according to DOA plant pest control manager, Larry Nakahara.
“When people refer to recent weeds, they’re actually referring to plants that were introduced four or five years ago and just recently got out of control,” says Nakahara, “If something had been done about this potential weed when it was first trying to escape, perhaps it wouldn’t be a weed today, but we have a tendency as humans to watch things; to say, ‘I think that’s going to be a weed,’ and ten years later, say ‘by golly, that’s a weed.'”
According to Denslow, intentional introductions make up 60 percent of the plants that become problematic. These come not just from nursery owners and landscape architects, but also from government agencies such as her own. By testing the plants already in trade, the WRA can identify those plants that are already a nuisance and put a red flag on those species that seem harmless now but are likely to be problems later.
Of course, the best scenario would be to catch the culprits at the gate. Trueman-Madriaga organized five more meetings in October to explain the WRA to landscapers, nursery owners and other interested members of the public. Those involved with the WRA hope this and further educational methods will be spur planters to consider what they are planting now in light of the WRA. Over and above that, they want to encourage planters thinking of bringing in new plants to submit them to a WRA evaluation.
Some may question the idea of introducing any new plants to Hawai`i when landscapers and gardeners can choose from thousands of native and naturalized species already here. But the landscape industry argues that its survival depends on the ability to design with new trees and shrubs.
“One problem is that they [the horticulture industry] need to find species that have particular characteristics that meet the needs of the site,” Denslow says, “They need a plant that can stand salt water or maybe survive in a very hot, dry, street setting. So, their list of choices is not as large as it initially seemsÉbut, we need to look for other species that are suitable for specified projects and work with the industry to find alternatives, while encouraging the use of those alternatives that are non-invasive.”
The Process
Fred Kraus, research biologist for Bishop Museum, says that plant invasiveness can be determined by looking at two factors: how the plant behaves in Hawai`i, and how it behaves in similar habitats elsewhere. Nakahara agrees that it is not enough just to look at the way a plant behaves elsewhere.
“Because a plant is a noxious weed elsewhere does not mean it will be a weed here,” Nakahara told Environment Hawai`i. “We have examples of plants that are weeds elsewhere but not in Hawai`i and vice versa.”
Although Daehler had begun evaluating the potential of the WRA two years ago, the project got a jump-start when Denslow approached him last year. After looking into systems used by South Africa, Australia, New Zealand, and one for trees of North America, Daehler concluded that Australian and New Zealand system was best suited for use in Hawai`i.
The system involves answering a series of 49 questions for each plant under consideration. Daehler had to reword just two of these questions to adapt the Australian system for Hawai`i. Questions cover topics such as a plant’s native climate and environment. Then the plant’s weed history is examined. Is it a problem elsewhere? After that, the plant is assessed for pest or annoyance characteristics. For example, does it have thorns or cause rashes? Finally, the ecology of the plant is considered. How quickly does it reproduce or does it need a special pollinator?
Each of these questions is given a rating and then the final score is tallied. If the plant’s score is less than or equal to zero, it is placed on a safe list and given a green light for use in the state. If it scores six or higher, then the species should not be planted. And if the score falls anywhere between one and five, it undergoes additional scrutiny. For these plants, Daehler has developed another series of questions. He says the whole process of evaluation takes four to six hours for most plants.
In the last year, with the help of three graduate students, Daehler was able to use the WRA to evaluate more than 200 species. To test its accuracy, Denslow sent surveys about the plants being evaluated by the WRA to about 20 experts on Hawaiian flora. They were asked about their firsthand knowledge of the plants’ behavior in Hawai`i. Were they, for example, growing in disturbed areas or in native ecosystems? Had they shown signs of being a pest? Because of the differing fields of expertise of those surveyed, answers varied. Still, when the results of the questionnaires were compared to the results of the WRA, there was agreement 80 percent of the time.
While this may seem high, Denslow says it’s not high enough to allow the WRA to be used as a reliable indicator of potential plant pests. Therefore, the screening process will not depend on the WRA alone, but will be coupled with evaluations and recommendations of an exotic pest plant listing committee modeled after similar panels in place already in California and Florida.
“It’s certainly a good tool to give you a heads-up on some species, but it’s not perfect,” Denslow says of the WRA. “It’s been the experience on the mainland that often government agencies are uncomfortable basing noxious weed decisions using predictive models. That’s why we feel it would be strengthened if coupled” with expert advice.
What it Won’t Do
In Australia and New Zealand, the WRA has regulatory force. No one is proposing that for Hawai`i, however.
“What we’re trying to do is provide the best information and education in the belief that many people want to do the right thing, if they knew what the right thing was,” Denslow says. The WRA would make it easier for them to do that. No longer would people have to fumble through numerous lists, wondering why the plants were on it.
“Because of the many different ecosystems in Hawai`i, there are lots of opportunities for things to escape,” Denslow says, “If we can raise the awareness of the general public and of the professionals to not plant things that are potentially invasive, than we can reduce the spread of the species and their impacts on the native Hawaiian ecosystems — not solve it, but reduce it.”
At this point, Daehler and his students are continuing to screen more species in the Hawaiian and Western Pacific trade. They will use the information gathered at the October meetings in designing ways to make results of the screening process more easily available to the public.
In any case, the WRA is not yet on the street. “Lots of questions need to be resolved,” Denslow told Environment Hawai`i. “I certainly don’t want to give anyone the idea that this is going to be ready by the end of the year and that it will have all of the answers, but the WRA is very promising. It gives us lots of useful information and it raises our awareness of potentially damaging species.”
— Miranda Watson
Volume 13, Number 6 December 2002