The impact of exotic species of plants in the Daintree Lowland Rainforest is increasing and as Karina Miotto reports "it's better to tackle a big problem while it's small". 

Assessing the weed problem in the Daintree Rainforest

Exotic species now account for about 15% of Australian flora. According to the Invasive Species Council, there are more than 2,700 alien plant species in Australia, with this number climbing by about 20 new species every year. 

Some of these plants have become a problem in agriculture and others are environmental weeds - exotic species of plants that have naturalised and cause the degradation of natural ecosystems. 

Environmental weeds are a significant risk to Australia's unique biodiversity and the financial cost to control them expands with a lack of action. 

The Department of Agriculture, Fisheries, and Forestry affirms that “the cost of weeds to agricultural industries is estimated at $4 billion a year. The cost of weeds to the environment is difficult to calculate but could be greater”.

Environmental weeds 

• Can destroy and degrade ecosystems
• Displace native plants that animals use for shelter, food, and nesting
• Inhibit natural regeneration  
• Change fire conditions (may be flammable) 

The Daintree Lowland Rainforest is at risk from environmental weeds due to the introduction of exotic species and disturbance of the ecosystem which favours their germination and growth.

Established weeds. 

Many ornamental plants (especially those species plants used as indoor plants) have their origins in rainforests and reproduce and grow in the shade of the canopy.

Commonly found in the Daintree lowlands are Arrow Vine (Syngonium podophyllum), Heliconia (Heliconia Heliconiapsittacorum), Torch Ginger (Zingiber spectabile), and Fishbone Fern (Nephrolepis spp). 

Singapore Daisy (Sphagneticola trilobata) was introduced to Australia in the 1970s as a garden plant. It is a vigorously growing ground cover that spreads rapidly and out-competes and smothers seedlings of native plants. It favours gaps in the canopy and can be seen on many roadsides in the Daintree lowlands.

Other weeds have been introduced through agriculture such as Guinea Grass (Megathyrsus maximus), Giant Bramble (Rubus alceifolius), Oil Palm (Elaeis guineensis) and Sickle Pod (Senna obtusifolia).

Next generation weeds 

Sleeper weeds are those invasive plants currently showing a low rate of increase in population size. As the numbers grow over time and achieve critical mass they are expected to become serious problems. Many species of exotic palms have been planted in gardens and their seedlings are now being seen in increasing numbers in the rainforest. 

New weeds 

New species of plants are being continually introduced to the Daintree lowlands as people acquire plants for their gardens. Inevitably some of these species will become weeds as other species have in the past. 

Increasing cost

The financial cost of not tackling the issue of environmental weeds in the Daintree lowlands could end up being enormous. The Daintree Daintree Lowland Rainforest is a significant natural, socio-cultural and economic asset and nature-based tourism in the Douglas Shire is responsible for earnings of $400m. This is largely dependent on an intact natural environment. As weeds become established they degrade the visual appeal of the environment which attracts visitors. Addressing the problem while it is small is in everyone's best interest. 

Fortunately, there is something we can do. 

Residents, landowners, and managers are taking action

Residents, landowners, and land managers in the Daintree lowlands are ideally situated to tackle the problem of environmental weeds. They already play a significant role in weed control on their own properties, while as volunteers with non-profit organisaions they develop and enhance community spirit. 

Daintree residents, landowners, and managers can help by:

• Learning to identify environmental weeds and the best methods of control  
• Sharing knowledge with neighbours 
• Getting hands-on with weed control on their own properties or getting help if it's a big job
• Joining community and non-profit organisation volunteer efforts
• Taking care not to disperse weed seeds or other propagules
• By not introducing exotic species of plants
• Many species are disturbance-affiliated weeds so avoid clearing and fragmentation of the rainforest as this opens up the canopy to light and will result in colonisation by exotic species
• Reporting new occurrences of declared species to Douglas Shire Council, for example, Pond Apple (Annona glabra)

How we are helping landowners and land manager 

We offer Grants to non-profit organisations, community groups and private landholders to assist with their practical conservation work in the Daintree Lowland Rainforest. 

Projects we are funding include:

• Tree planting and maintenance 
• Managing natural regeneration through the removal of environmental weeds

Please see more information here. 

Weed identification is a good starting point

Karina Miotto is a rainforests advocate and journalist who visited the Daintree Lowland Rainforest in 2022. 

Environmental weeds found in the Daintree Rainforest

• Ageratum conyzoides (Billygoat Weed)
• Bidens pilosa (Cobbler's Pegs)
• Brilliantaisia lamium
• Calopogonium mucunoides (Calopo)
• Centrosema molle (Centro)
• Clerodendrum paniculatum (Pagoda Plant)
• Colocasia gigantea (Giant Elephant’s Ear)
• Costus speciosus (Costus)
• Cyperus aromaticus (Navua Sedge)
• Dieffenbachia (Dumb Cane)
• Dracaeana fragans (Dracaeana)
• Elaeis guineensis (Oil Palm)
• Elephantopus mollis (Tobacco Weed)
• Eleutheranthera ruderalis
• Euphorbia heterophylla
• Heliconia psittacorum (Heliconia)
• Hyptis capitata (Knob / Pepper Pot Weed)
• Hyptis suavolens (Horehound)
• Ipomea indica (Blue Morning Glory)
• Lantana camara (Lantana)
• Mimosa pudica (Sensitive Plant)
• Mitracarpus hirtus
• Nephrolepis (Fishbone Fern)
• Odontonema tubaeforme (Red Spike)
• Panicum maximum (Guinea Grass, now Megathyrsus maximus),
• Praxelis clematidea
• Pseudelephantopus spicatus (False Elephant Weed)
• Pueraria phaseloides (Tropical Kudzu)
• Rubus alceifolius (Giant Bramble)
• Sanchezia spp (Yellow Candles)
• Selaginella willdenovii (Electric / Peacock Fern)
• Senna obtusifolia (Sickle Pod)
• Sida rhombifolia (Common Sida)
• Solanum torvum (Devil’s Thorn, Devils fig)
• Spathodea campanulata (African Tulip Tree)
• Sphagneticola trilobata (Singapore Daisy)
• Stachytarphetta spp (Snake Weed)
• Synedrella nodifolia (Cinderella weed)
• Syngonium podophyllum (Arrow / Hippie Vine)
• Tetracera nordtiana (Fire Vine)
• Thunbergia grandiflora (Blue Sky Vine)
• Urena lobata (Urena Burr, pink burr)
• Youngia japonica (Japanese Hawkweed)
• Zingiber spectabile (Torch Ginger)