If you’ve been reading my blog for a while you will know that I’m very concerned about the encouragement of the use of invasive or potentially invasive species in permaculture (you can see where I’ve written on the subject here and here).
Now the folks at Milkwood Permaculture have thrown up a curly one – they’ve just posted on how Madeira Vine not only has edible leaves and tubers, but is widely eaten and cultivated in Japan, where it is known as “land seaweed” (okawakame).As they point out, Madeira Vine is an already “adapted, perennial, zero footprint and highly nutritious food plant” with the following characteristics which are desirable in a food plant:
- “It grows without much assistance, is hardy and produces prolifically.
- It requires minimal cultivation.
- It dominates an area where it is planted (meaning far less weed control is needed)
- It is spread only* by humans and by water flows distributing the bubils – an easy factor to contain with good design.”
The Milkwood guys are planning on having it as a food plant in their garden. They recognise that it is a potential problem, and will manage it by eating it and stopping it from spreading.
So, should we incorporate Madeira Vine into our permaculture food production?
My first question would be: Just how weedy/invasive is it really?
Madeira vine grows prolifically at rates of up to 1 m per week in high-light environments. It produces large numbers of subterranean and aerial tubers that not only act as reproductive bodies, but also provide the plant with a carbohydrate source that enables it to survive through difficult times. As a consequence, Madeira vine can tolerate a range of adverse conditions including drought, snow and frost, and it has been found growing in areas as diverse as rainforests, riparian fringes, rocky outcrops and frontal dunes (source). This same ability to tolerate adverse conditions also means that the tubers can survive for very long periods of time in suspended animation, before they experience the right conditions to shoot (source).
The vine reproduces through the proliferation of aerial tubers and also from rhizome (subterranean tuber) fragments that may be broken off (source). The aerial tubers can persist for two to 15 years and rhizomes for five to 10 years, with tuber germination rates of up to 70 per cent (source). Although Madeira Vine is widely believed not to set seed in Australia, up to 5% of dried flowers collected from southeast Queensland were found to contain germinable seed (see #Vivian-Smith et al, below).
Dispersal is believed to occur primarily* via human spread (cultivation for ornamental purposes, disposal of vegetative material and tubers, e.g. in green waste (source), or being spread by machinery and/or gravel during road construction). However it also spreads downslope under the influence of gravity and water movement from ridges and down watershed, and via floods (source).
Saying that it is spread primarily by humans needs to be considered in relation to just how widespread it is, what a significant destroyer of habitats it is once established, and how extremely difficult it is to eradicate once established. Here is how the Environment Australia weeds database summarises the facts about Madeira Vine:
Madeira Vine is a Weed of National Significance (WONS). It is regarded as one of the worst weeds in Australia because of its invasiveness, potential for spread, and economic and environmental impacts.
Madeira Vine has aggressive vegetative growth which competes with and replaces other vegetation, and is difficult to control once established. Its aggressive nature gives it the potential to smother other desirable plants. Its sheer weight is capable of breaking branches off trees, thereby reducing them to poles, potentially causing collapse of the rainforest canopy (ISSG 2006). It restricts light and thereby prevents germination of desirable native species (Harley undated).
Should we then include Madeira Vine in permaculture food production? I think there are two things to take into account before making a decision on this.
First, the permaculture ethics of care for the Earth and care for people. The potential impacts on the Earth from Madeira Vine escapes are obvious (see the sources and photo above) and well documented, as are its impacts on the people whose properties and amenity are impacted.
Second, based on an assessment of invasiveness and impact, Madeira vine was ranked 5th worst of1060 naturalised south-east Queensland plant species (#Batianoff & Butler, below). How are you going to ensure that:
- no seed is set, and neither seed nor tuber material is distributed by animals, or other agents of dispersal, including water (i.e. the area where you will grow it will never flood or be exposed to high volumes of water runoff;
- everyone who works on your garden or caretakes for you while you are away is as careful as you would be not to allow any dispersal of aerial tubers, (fragments of) rhizomes or seeds;
- before you move on, you will have somehow removed all aerial tubers and every last fragment of rhizome before you leave, or failing this, you have some guarantee that the next landholder is going to take the same careful management approach as you?
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*I consider the statement that it is spread “only by humans and by water flows distributing the bubils – an easy factor to contain with good design” to be dangerously simplistic for a number of reasons. First, once a Madeira Vine has established itself in a vegetated area it does not sit and wait for humans or water flows to come along and move its tubers or rhizomes. The tubers are spread naturally when they fall from the adult plants where they have climbed up and across the canopy (often a considerable distance) from where they originally grew. Second, anywhere that an established population of Madeira Vine grows over a waterway that even only occasionally flows, this will distribute the plant to any and all areas downstream. Third, saying that it is spread “by humans” without mentioning the many ways in which human activity can spread the plant, or the very long viability period of the tubers, gives a very misleading impression of the ease with which human activity can (even unwittingly) result in spread.
Here is a rather more informative account of how it is spread:
The most common means of reproduction and spread is via asexual tubers formed on the roots and stems. Prolific numbers of aerial tubers are produced throughout the year, which drop to the ground when mature or in response to stress. Research indicates that aerial tubers can persist for two to 15 years and subterranean tubers for five to 10 years, with tuber germination rates of up to 70 per cent. In areas of heavy infestation, soil tuber densities are up to 1500 per m2. Madeira vine is also capable of shooting from sections of severed vine.
Dispersal occurs primarily via human spread such as cultivation for ornamental purposes, disposal in green waste, or spread by machinery during road construction. It can also spread via gravity and water movement from ridges and watersheds or during floods. Mammals and birds may also play a minor role in localised spread.
While seed production is believed to be rare in Australia, research indicates that up to 5 per cent of dried flowers collected from southeast Queensland contain germinable seed. It is speculated that seed set and germination may only occur under ideal environmental and seasonal conditions.
Sources which aren’t linked above:
#Vivian-Smith et al, Alan Fletcher Research Station QLD Unpublished data (cited in this source)
#Batianoff, G.N. and Butler, D.W. (2002). Assessment of invasive naturalized plants in south- east Queensland. Plant Protection Quarterly 17: 27–34.