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[personal profile] halifaxearthtech
It seems to be quite the debate in Permaculture discourse as to whether species can or cannot be 'invasive'. I feel it necessary to add my $0.02.

To give some context, the Prairie provinces find themselves in a heated debate surrounding 'invasive species' (I can't find the link at the moment), with pesticide companies standing to gain from municipal laws mandating the removal of 'invasive species'. Sometimes this even extends to species that are native to the area such as the bulrush. It is advocated that the stems of these plants be cut and Glyphosate (Roundup) pesticide poured into the stem of the plant to kill it. This creates a toxic environment in wetlands such as ditches, and compromises the ability of these ditches to purify rain runoff before it gets into larger bodies of water. I almost don't need to say that this is not an ideal situation.

Plants have enjoyed international travel since the beginning of life on earth, and no plant is truly native. There has always been the odd far-faring bird pooping a seed onto a new continent, and the immigration of life on new volcanic islands is well documented.

When I speak of invasiveness it's within the context of the massive influx of new species from the Old World to the New world in what is a geological blink of an eye. Yes, nature will sort it out and in a few million years these new plants will find a niche and be controlled by lifeforms designed to prey on exatreme concentrations of one species. They are even now adaping to different conditions from the home continent. Diversity will prevail, and those native species who become extinct from the events of colonization will be out of luck. Pouring glyphosate into stems will do little to affect this process.

However, my definition of invasive is different from whatever these municipalities are looking at. Permaculture looks at a human-scale of time as well as geological time. Some people talk about introducing species such as goutweed into food forests because they are (marginally) edible and a habitat for predatory calcid wasps. However plants like goutweed will choke out other plants in a food forest to the extent of creating a field in which there is no understory or forb layer aside from goutweed. I don't know where the plant comes from, but the controls that existed in its native habitat are clearly lacking here. Such people, much as I love them, are exhibiting a lack of insight grounded in observation. They are these plants that I call invasive, those that don't play well with others on a human scale, and threaten our survival in the time interval before nature creates balance again.

Another example is Phragmites Australagus, which chokes out bulrushes from their native habitat, threatening moose and other animals that benefit from their concentration of carbohydrates and proteins, including us. P. australagus is useful to thatch roofs, but it's a loss of productivity for the land, and a reduction of the possibility for diversity and variety and thus productivity. A plant with similar tendencies to P. australagus is Japanese knotweed. Now I enjoy eating knotweed sprouts in the spring, and there is doubtless potential to use the abundant biomass from their stalks. But it would be folly to introduce it where it is not because it does not play well with others, and it creates a climax condition where competing trees that would shade it out cannot be established. Plus there's already lots out there to take from.

I differentiate 'invasiveness' from 'having a high rate of reproduction'. Norway maples as far as I know play well with others (edit: they don't, they'll poison the ground beneath them in a process known as alleopathy). As much as I have several problems with Norway maples that would fit best in another article, anyone who calls them invasive has not seen the behaviour of a tree in an intact forest, which must seed tens of thousands of seedlings every year just to have a chance that one will find a patch of available sunlight. In the city, this just means the trees will try to recreate the forest where they are. This is more of an indication of the landscape than the tree. I would prefer to see the same behaviour in a tree that is slightly more useful to us.

I use the word invasive because it best communicates to people the tendencies of a plant that excludes all others (through rhizome mats or a high rate of seeding), create climax conditions, and to be nearly impossible to eradicate in a human-based interval of time, even with fossil fuel-aided human effort. The possibilities for redundancy and resiliency are limited. The word 'invasive' still has relevancy to serve as a warning to those who garden.


Perhaps the word invasive can be most usefully be broken down into at least 4 categories;

Difficult to remove,
Does not play well with others,
Aggressively sends out runners or rhizomes
Aggressively seeds and/or remains in the seed bank

Date: 2013-04-18 11:35 am (UTC)
camillanightshade: (Default)
From: [personal profile] camillanightshade
An interesting post, i learn much from you.


halifaxearthtech: (Default)

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