I think a strong argument needs to be made to counter the widespread campaign against so-called invasive plants, which, while probably well-intentioned, is demonstratively misguided.
The current herbicidal war being waged in B.C. – mostly along our highways against arbitrarily selected targets – couldn’t better illustrate why I say this.
First, along comes the most invasive, harmful foreign species of them all and clear-cuts, bulldozes and paves a ribbon of ecosystem destruction for a road, then expresses dire concern if, among the mix of species that quickly becomes established, there are some non-natives that make an appearance.
Most “invasives,” whether indigenous or exotic, could perhaps more appropriately be called “opportunistic.” Very few gain a foothold in intact ecosystems, but rather almost always appear in human-disturbed landscapes such as home-lots; industrial sites; road, rail and power line rights-of-way; waste places; and abandoned farms and fields. Even then, few crowd out native opportunistic species. Instead, they almost always add to biodiversity, rather than diminish it, as predators, pathogens, parasites, other plants and time play their roles until a balance is achieved.
Although “invaders” are said to form monocultures, most don’t. For example, Lythrum salicaria (purple loosestrife) is called “an aggressive invader” that can form “dense, nearly monotypic stands” (Hight, 1993) and “overrun a North American wetland and reduce its wildlife value to roughly that of a parking lot” (Bight 1998. Significantly, Bight makes no pejorative comment about parking lots; one wonders how many square miles of concrete paving exists compared to loosestrife occupation). However, “Anderson (1995) reviewed 34 papers on loosestrife and found records of 29 native species of wildlife using the plant, and many records of native species out-competing it… In a study of 41 plots in Ontario, no significant difference in vascular plant species richness was found, regardless of the presence of loosestrife.”
Other studies – one involving 258 plots – confirm these findings. (1)
At the same time, ironically, some native monocultures exist, Typha (cattails) and Phragmites (reed grasses) are but two well-known and widespread examples. (1)
The currently targeted species on the Sunshine Coast, Polygonum japonica (Japanese knotweed) “is considered an ‘aggressive invader’ of riparian areas [river margins, banks, and adjacent wetlands]. Yet in a study of five rivers … waste ground and land drainage works had the highest frequency and abundance of the knotweed, and natural, semi-natural and grazing land had the lowest frequency and abundance (Beerling, 1991).” (1)
Speaking personally, I have never found it along any local creek and can only recall seeing it growing on private land in two localities, although I imagine that it does exist on other properties. I intend to introduce it onto mine because it provides nectar and pollen for many beneficial insects; because it is a delicious edible – the fresh shoots, lightly steamed, taste like slightly lemony asparagus (consuming spreading plants is called “control by eating”); in order to study it more closely; and because benevolent methods of eradication, if desired, can easily be employed. Contact the author for an onsite consultation.
Cytisus scoparius (Scotch broom) is another plant that has been singled out for special hostility, despite having 39 uses, as discussed by Grieve (1931). (4) It, too, is “utilized by a wide variety of native organisms” (Theodoropoulos, 2003) and, importantly, is a beautiful nitrogen-fixing shrub that begins to heal damaged sites – an “early seral,” shade-intolerant plant that inhabits non-forested communities on exposed mineral soils that are drier than those favoured by Alnus rubra (red alder).
Alder is perhaps our closest native equivalent to broom, playing a similar role after site disturbance, also “enhanc[ing] the supply of available soil nitrogen,” thus making it “suitable as a temporary nurse crop for shade-loving conifers.” Paradoxically, it can also form “dense stands in the initial stages of primary … or secondary succession” and “may hinder regeneration and growth of conifers.” (2)
Here is an aggressive native species that can prevent and delay the re-growth of coniferous forests for decades, yet I have not heard of campaigns of extermination against alders. Why the prejudice?
What criteria are being used to determine which plants to try to exterminate? Perhaps Rubus procerus (Himalayan blackberry) will be next, an introduction a “thousand times” commoner on the Coast than either of the other two species. Why isn’t it being attacked? Is aerial spraying perhaps being considered? And what of all the grasses we see everywhere? About 50 of the approximately 300 kinds found in B.C. are non-natives. (3)
Can we expect to have these foreigners identified and poisoned or rooted out by citizen groups? It seems having some selected immigrants living peacefully amongst us is trumped by spending millions to spray with Monsanto chemicals.
Cash and chemicals, however, are only part of my concern. The irrationality of the pogrom against certain plants deemed a menace is what chiefly offends me, and prompts me to write, as well as the time and attention being devoted to spreading public fear that is not based on careful thought and the facts of the matter. The hysteria.
Many agents spread seeds: wind, fresh and salt water, birds, mammals. Recent studies have even determined that continental drift alone cannot account for the fact that pre-colonial, “indigenous” species in North America are often of the same families and even genera that can be found across oceans on different continents. What all this means is that natural forces have been spreading plants around the globe long before Homo sapiens began doing so.
Who is to say which plant is native and which is not? For how long must a species be established in a region before it is deemed to be a local? Does any part of nature other than humans care if a new life form makes an appearance anywhere? Can it ever be said that an ecosystem that is altered by a new introduction is damaged by that introduction? I suggest the plants be left to fight it out amongst themselves until an area is needed for some valid anthropocentric purpose, such as growing food, at which point they become “weeds.” Even then, an intelligent mix of species, both native and non-native, is always called for in any carefully designed agriculture: Both alder and broom can be helpful in an orchard; so-called weeds such as lambs quarter, dandelion, chickweed, purslane, sorrels and clover, to name a few, are important additions to my permaculture.
There are many reasons to suppose that those waging the war on so-called invasive plants might need to reconsider the foundations of their beliefs, and examine the possibility that bad science and hidden agendas inform their actions. I think this war should be opposed and stopped.
Peter Light, permaculture design practitioner, consultant, speaker and teacher: [email protected], 604-886-8527.
References:
1. Invasion Biology, A Critique of a Pseudoscience, Theodoropoulos, 2003;
2. Indicator Plants of Coastal British Columbia, K. Klinka, et al, 1989;
3. The Grasses of British Columbia, Hubbard, 1969;
4. A Modern Herbal, Grieve, 1931.
See also Where Do Camels Belong, the Story and Science of Invasive Species by Ken Thompson, and The New Wild, Why Invasive Species Will Be Nature’s Salvation, by Fred Pearce.
