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Pressures on the World Heritage Area - Invasive Weeds
Weeds
A weed is a plant in the wrong place, with the
potential to take over where it’s not wanted. Some previously
well behaved plants have become outlaws in the Wet Tropics, thriving
in local conditions, invading natural habitat and farmland, crowding
out native species, or blocking waterways.
Once a plant is identified as an environmental
or economic threat and a control method is found, it can become
a 'declared pest', with action required wherever it occurs.
Local councils and landholders may be required to eradicate a declared
plant, or reduce the incidence of the plant.
Weeds often thrive in disturbed areas of the rainforest,
or along edges and breaks in the forest, so protecting the forest
and keeping it in good health will discourage the invaders.
The Queensland Department of Natural Resources and Mines website will tell you all about declared weeds, environmental weeds, identification of weeds and control methods.
Here are some varied examples of weeds:
Miconia (Miconia calvescens) is a shade tolerant ornamental tree from South America. It produces large numbers of seeds which are dispersed by birds, enabling it to spread quickly over a wide area. Miconia prefers a rainforest habitat and has had a major impact on rainforests in Hawaii and Tahiti.
African
tulip (Spathodea campanulata) is an ornamental
tree, valued for its red tulip-shaped flowers. It is a highly invasive
plant, producing huge numbers of wind dispersed seeds which seem
to thrive wherever they land. When the unsuspecting landholder tries
to cut down an African Tulip it sends up new seedlings along the
length of its root system, turning one problem tree into dozens.
Cabomba
(Cabomba caroliniana) was brought to Australia for use in
aquaria and has proved to be highly invasive. Just a small segment
of stem can produce a cluster of feathery foliage, eventually blocking
waterways.
Dutchman’s
pipe (Aristolochia) is a rainforest vine and
a food plant for the magnificent Cairns birdwing butterfly. Take
great care in choosing a Dutchman’s pipe for your garden -
there is a Brazilian imposter which attracts the butterfly and then
poisons its caterpillars! The poisonous interloper is from the same
genus as the native Aristolochia, but can be identified by its round
petals with a white protuberance.
Hurangana
(Hurangana madagascarensis) is a large tree growing up to
25 metres. It produces bunches of small flowers and orange-brown
fruit and may have been introduced as an ornamental garden tree.
Hurangana spreads via its numerous bird dispersed seeds and suckering
roots and can take over in disturbed areas and along the edge of
forests. It has also been found in undisturbed forest, thriving
in gaps created by fallen trees and land slips.
Pond
apple (Annona glabra) is one of the worst invaders
of the Wet Tropics. Its tolerance of salt and immersion in fresh
water enables pond apple to invade melaleuca wetlands, where it
forms a dense understorey and prevents young melaleucas from developing.
Fire and chemicals can be used against pond apple, but both need
careful management. There is more information on the Pond Apple page.
Salvinia
(Salvinia molesta) has escaped from garden fish ponds to
cover waterways with a thick mat of fleshy leaves, blocking sunlight
and causing underwater plants to die. The decomposing plants in
turn cause oxygen levels to drop, killing aquatic wildlife.
Sanchezia
(Sanchezia parvibracteata) is a South American shrub with
dark green yellow-veined leaves and clusters of yellow trumpet-shaped
flowers. Broken fragments of sanchezia can take root and thrive,
producing dense thickets along river banks. This invader can be
found in tropical gardens - plants and trimmings should be disposed
of very carefully.
Thunbergia
(Thunbergia grandiflora) was introduced as a garden creeper
but has proven to be a spectacular invader of rainforest. From lowland
forest edges and water courses, thunbergia climbs and smothers rainforest
trees, eventually reducing them to dead stumps. Physical attacks
on thunbergia usually helps it spread. Herbicides have been used
with success.
For more information on how to identify weeds and manage them:
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