Cumbungi has gained a cursed reputation as a troublesome, semi-aquatic weed, both within Tasmania, across southern Australia and in other continents. However, on closer investigation, cumbungi has a number of important attributes, which deserve recognition.
Of the three species of cumbungi in Tasmania, two are indigenous and one is an exotic relative from Europe. All of these tend to be lumped together and dismissed accordingly within the environmental weed basket. However, this does not account for their traditional uses, as well as their water purification role, associated with the "in vogue" technique of constructing created wetlands to improve water quality.
Cumbungi are tough perennial plants that thrive in fresh or lightly brackish water of less than 2 metres in depth. Its ability to use slow flowing, nutrient rich water in irrigation channels, dams, lakes and along river banks, enables it to dominate these preferred habitats.
The long strap like leaves and stems die back in winter, storing their reserves in their rhizomatous roots and re-sprout vigorously again in early spring.
The genus name Typha is an appropriate Latin name for these plants, since it derives from the Latin word which means 'marsh'.
The introduced species is Typha latifolia. It is usually known by the common name 'cumbungi', although in its native Europe, it is often referred to as 'cattail' or 'pole-rush' (meaning pool rush).
The two indigenous species are Typha domingensis (narrow leaf cumbungi) and Typha orientalis (broadleaf cumbungi), are both frequently known as bulrush, or bullrush (it has nothing to do with bulls).
Without delving into the complexities of their botanical physiology, the following information can enable a distinction to be made between the weed and native species.
Although the leaves of Typha latifolia are distinctly shorter at 1 metre, compared with the 2 metre lengths for the indigenous species, the colour of the summer flower heads provides a better clue towards discriminating the weed species from the local species.
Their single flower heads consists of an upper loose spike of the male flower, above the dense cylindrical spike of the female flower. Each female flower head contains up to 200,000 parachute-like seeds which are easily dispersed by gentle winds.
The weed species has a blackish brown female section, while the others are distinctly lighter in colour, with Typha domingensis having generally longer and thinner female flower heads than its native cousin.
Once the female flower is matured, the easily released fluffy seed (pappus) ensures endless fun and games for kids as they proceed to generate thick white clouds of tiny floating seeds during duelling antics with their long flower stalks.
The weed classification for cumbungi, relates to the concept of 'over successful native plants'. This in turn begs the question as to why these indigenous plants have become over successful?
Over successful indigenous plants result from subtle environmental changes which disrupt the existing dynamic equilibrium amongst the members of their vegetation community. These gradual changes tend to favour one species, whilst subduing other species. Ideal conditions soon allow plant(s) to proliferate within its ecosystem.
Often these environmental changes are primarily a response to human impacts. However, the accelerating greenhouse effect and natural long-term climatic perturbations work in favour of some native species.
For cumbungi, the specific human impacts favouring its dominance developed from both the traditional aboriginal and recent white man fire regimes, which have been imposed on the landscape. These were exacerbated by the progressive eutrification of waterways following the unsustainable agriculture practises of chemical fertilizers use and bare earth cultivation.
These techniques bared the soil resulting in heavy rains transporting the soil into and along the drainage systems. Slugs of nutrient rich sediment provided the ideal substrate for flourishing of the aggressive cumbungi plants. Their thick fast growing rhizomes acted to trap more and more sediment, thus promoting their further exploitation of these ideal conditions. Over time they have clogged up many fresh and brackish shallow water bodies including natural wetlands, farm dams, backwaters of rivers and creeks.
The floury rhizomes of cumbungi provided a staple food once prepared in the traditional manner. This preparation required hand length root sections to be peeled and placed in close proximity to a fire to soften. These sections would then be twisted and shaken to loosen the fibres to enable glutinous flour to be extracted. Once dried and moulded it was baked on the hot fire ashes in the form of a damper.
Young succulent leaf bases were also eaten, giving a pea like flavour. If the water was murky or polluted, it became tainted and inedible.
The left over fibre was tediously drawn out to begin the tedious process of making strong, resilient string. The women rolled the moisten fibres on their knees to form long continuous strands. These were then woven together to make stronger 2 or 3 ply string. Basket, dillies or decorative artefacts were frequently available for the aboriginal families to collect berries, seeds, shellfish etc or use as storage and transport containers.
The reason for the importation of the weed Typha latifolia into Tasmania, relates to the concern by the general populous that boating and swimming could be made safer by supplying ample lifebuoys etc in boats and at swimming venues. This concern was exacerbated by the news of the huge numbers of drowning, associated with the sinking of the Titanic.
The light fluffy "kapok" like seed heads of the cumbungi was ideal for compressing into floats and other buoyancy devices such as lifebuoys. To ensure ample raw material the weed species of cumbungi was introduced from Europe and that initiated the weed problem of today.
Constructed wetlands are taking the water purification process into the 21st centaury. They are being used to protect rivers, lakes and dams from overloads of nutrients, bacteria, polluted and suspended sediments as well as pesticides. With careful design they can achieve substantial improvements to water quality by purifying and filtering polluted water, prior to its controlled release into down stream watercourses.
Stormwater, sewage and effluents from mining sites, piggeries, dairies and hen batteries can be effectively treated by this technique, which also has the added advantages of providing pleasant recreation areas for walking and habitats for birds and wildlife.
Constructed wetlands should be designed to slowdown water flow through the wetland to allow sufficient time for the purification processes to operate in order to reduce the water born contaminants. Aquatic plants such as the native cumbungi, rushes, sedges and reeds are the key to this pollution reduction process. They not only absorb nutrients for their rapid growth, but also provide the sites on their roots for the hungry pollution-eating microbes to attach and munch up all the organic wastes whilst neutralising their toxicity.
Within created wetlands, these plants such as cumbungi also reduce the velocity of the entering water, allowing polluted sediments to fall out of the water column. This then enables the process of adsorption of nutrients and pollution such as oils and agricultural wastes, onto these sediments. Once trapped, these water polluters can be regularly dug out of the wetland and removed permanently for further dry land remediation.
In order for Cumbungi to be used as preferred created wetland plant, it needs to be effectively controlled. To prevent cumbungi dominating the other wetland plants, frequent harvesting of cumbungi is needed. This along with its careful placement in contained locations, isolated by at least 2 metre deep water channels, will ensure that it does not invade the whole of the wetland system. Cumbungi's main control techniques include, maintaining water depths of greater than 2 metres, cutting back the actively growing plants regularly below water level, mechanically removing the whole plant when in winter dormancy and /or spraying with frog sensitive Bioactive Roundup. It needs to be recognised that, like some other wetland plants planted as water cleaners, their efficiency is substantially reduced if winter conditions prevail. This will cause them to go into a period of dormancy.
However on the positive side an added bonus is gained from regular harvesting of cumbungi, since it produces copious organic matter. This is easily converted into nutrient rich mulching and composting material ideal for enhancing any organic gardening or agricultural pursuit.
Phil Watson