Doctors prescribe attitude change for World’s weediest city
Researchers say responding to the threat of weeds early rather than waiting until plants become weeds is crucial for
curbing Auckland’s rampaging weed problem.
The Auckland Regional Council has proposed a ban on sales of Phoenix, bangalow and Chinese fan palm trees, as these are
spreading into and threatening native bush. Palm enthusiasts have expressed disbelief that the trees are a threat now,
after more than a century in New Zealand. They also say self-sown palms can easily be weeded out.
A Phoenix palm discovered growing in a native bush patch in Auckland. Photo: Landcare Research
Nikau palm and bangalow palm seedlings - spot the difference. Photo: Landcare Research
Landcare Research botanist Dr Peter Williams says many weeds establish when people fail to act on early signs that
exotics are spreading.
“New Zealanders tend to wait to assess how a potential weed will impact on the environment. But by then it’s too late,
because the plant has often already spread and become a weed.
“The didymo alga is an extreme example of how quickly a weed can spread. Rapid response may not always stop aggressive
invaders, but it does improve our chances.
“We need a shift in culture towards taking pre-emptive action, even if that means erring on the side of caution.”
Dr Williams says invasive species which spread slowly are known as “sleeper” weeds. Like secret agents, sleeper weeds
appear benign and relatively inactive, sometimes for decades. Palms take many decades to establish because they are slow
to produce seeds. But once they do, birds distribute the seeds far and wide and the trees’ spread is inexorable.
“Just because palms spread slowly, this does not make them less of a threat,” Dr Williams says.
“Hieracium and old man’s beard took decades to begin to spread.”
Landcare Research scientist Dr Margaret Stanley agrees, and says that weeding out stray palm trees is not as easy as
many believe.
“It means extra time and expense for community groups who are weeding native forests.
“Also, bangalow palm seedlings appear identical to those of our native nikau palm, which causes considerable confusion.
“Nipping weeds in the bud is by far the best approach.”
Facts on Auckland’s weedy woes:
Auckland has the dubious honour of being the weediest city in the world, with 220 weeds (and climbing). It has more than
10 000 exotic plant species (compared with about 400 natives), and each year an average of four species naturalise
(escape cultivation and reproduce in the wild – with great weedy potential.) There are currently 1100 naturalised exotic
species in Auckland. Weeds displace native plants, alter soil chemistry, and drastically reduce food for native animals.
ENDS