The Hawaii- Pacific Weed Risk Assessment (HPWRA)
What is the HPWRA?
A vetting process for plants. That uses published scientific papers rather than anecdotal information to answer a set of 49 questions . This tool is repeatable (anyone can answer the questions and come up with the same answer) and transparent (all references are listed with the answer). It asks if humans are likely to disperse the plant. This can give us an idea of how many repeated introductions and more chances the plant may have to escape cultivation. It also asks:
- Is this plant a weed in other parts of the world?
- Is it shade tolerant? This can predict a plant’s ability to establish in a closed canopy forest.
- Do the seeds remain viable in the soil for more than a year? This lets us know if the new plants will continue to germinate long after eradication.
- Are the seeds dispersed by animals/wind/water/birds? This tells us how far a seed can move beyond its parent plant.
Why do we need the HPWRA?
To predict if a plant is likely to be invasive. Most people wouldn’t go on a blind date or to a job interview without researching a person or company. We should scrutinize our plants the same way. If your potential date is a married you would choose another date. If the CEO of the company you are applying for is in prison for embezzling you would chose a new company. There are between 250,000 and 400,000 flowering plants in the world, and about %10 to %15 will naturalize here in Hawai’i. Out of that, a small number (%1 to %3) will become “super weeds”. These aggressive invaders change the ecosystem by making monotypic stands. This affects and changes the soil, runoff, groundwater recharge, native seedling recruitment, native animals and fire patterns.
How do we know the HPWRA works?
The results of a 2002 study confirmed the HPWRA is %95 effective in predicting major pests and %85 as non-pests. Using a version of the Australian Weed Risk Assessment that was modified to fit Hawai’i’s climate, 200 plants were assessed using the newly formed HPWRA. At the same time experts in the fields of forestry and agriculture, along with botanists and weed scientists, rated the plants using their professional knowledge (25 professionals in all). The plants were rated: major pest, minor pest and not a pest.
What do the numbers mean?
Its categorical rather than a grade. A low risk designation has a score of 0 or less and indicates the plant has characteristics that make it unlikely to be invasive. Some low risk characteristics include: being highly domesticated (invasive traits are often bred out over 20 generations of cultivation), shade intolerance (can’t establish in a closed canopy forest), palatable to animals (animals help keep the plant from seeding) or requires a specialist pollinator (no pollinator will produce no viable seeds). Evaluate designation is a score range of 0 to 6 and indicates there may not be enough published information to answer whether or not a plant will stay in its intended location. The evaluate designated plant will re-evaluated once more information becomes available and will get a designation of low risk or high risk. A designation of high risk is given to plants with a score of 7 or more. High risk plant have trait that make the plant likely to invade a landscape and become a problem to our health, economy and way of life.
What does the HPWRA have to do with me, my business and my community?
It gives us the power to fight invasive species by simply not planting them. It helps save native ecosystems! Landscaping in our homes and businesses is a showcase for plants. Show your friends and neighbors you care by planting pono. Some people think if they don’t see a plant invading it’s not a problem. Hawai’i is a huge place and plants can be invading in landscapes from from our eyes. Becoming an informed citizen of Hawai’i and listening to experts that assess you plant will go a long way in protecting our native flora and fauna.