On The Proposed (And Actual) Banning Of Purple Loosestrife!

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"Purple loosestrife growing in Tommy Thompson Park on Toronto's waterfront. Author photo."

Seven years ago this August, I returned from a three week trip across Canada, from Osoyoos, British Columbia, to Pasadena, Newfoundland. We travelled by small plane, large plane, fast train, slow train, and car. I was head of a judging team for Communities in Bloom in its first year of operation, and while the trip was to judge competing municipalities in eight provinces, we also had a great opportunity to observe the country horticulturally in general.

In every province (except Newfoundland, where there is very little), purple loosestrife (Lythrum salicaria) was at its best! Media reports have once again been condemning the plant, a common herbaceous garden perennial that it is claimed could well, in just a few more years, cause the demise of the few wetlands that Canada has left. The plant grows equally well in sun or part shade, but definitely prefers moist conditions. Its tall spikes of carmine-pink flowers are displayed from mid-June to late August, and it’s generally a very good perennial for garden use, particularly if you have a pond or damp area.

However, biologists and naturalists are calling for a government ban on the sale and propagation of the plant which they say, as a non-native, has no natural predators and is quickly taking over our already-too-few wetlands, and causing them to fill in. 

I must point out that to call for an outright ban is not only a gigantic over-reaction, but also it simply will not work. It's decades ago now that the common barberry (Berberis vulgaris) plant was banned because it was said to be an alternate host to wheat rust disease. That ban has been anything but effective! You can see common barberry growing wild and in abundance still, and, what about other similarly introduced non-native plants. Common tansy (Tanacetum vulgare) is in full yellow bloom in August in many areas, and no one seems to be suggesting it be banned. Viper's bugloss or blue thistle (Echium vulgare) is spectacular many years. It is widely distributed and came from Europe, but there is no call for it to be banned, and it too prefers moist areas. 

Purple loosestrife is a beautiful garden plant with a long blooming period, insect and disease resistance, and for most gardeners is safe to plant from a wetland point-of-view. Virtually all of the plants sold in Canada are cultivars developed by our own Agriculture Canada at their famous research station in Morden, Manitoba.

In response to continuing negative publicity, mostly from writers who just follow what others be-fore them have written, I decided to do a little investigation into the whole subject. I found that the possibility of purple loosestrife taking over other common wetland border plants such as cat-tails and natives such as willows is highly unlikely. 

My late colleague Fred Dale had a farm pond edged with natives. He pointed out that naturally introduced purple loosestrife had been pushed right out by the native willows and cedars, and cattails. Just what is behind the campaign to ban this beautiful, useful plant? It is a well-known fact that the anglers & hunters are the main organization pushing for a ban. These people don't like loosestrife around their fly-fishing ponds because they cannot fish from the edge due to its rapidly expanding growth. They would also, by the way, like to see cattails reduced to about 50 percent of their present numbers. 

Will it in fact be responsible for the complete demise of all of our wetlands, as is promoted by the self-interest groups? Do you realize wetlands remain in existence for only a period of time--regardless of so-called predators such as loosestrife? Our individual existence is but a tiny fraction of the life of the planet. For us to say that wetlands are being destroyed entirely during our lifetime is rather self-serving. In fact, over the next 100 years, virtually all the wetlands we now know will cease to exist, and many new such lands will be formed. Observers of the natural progression of the planet's landform confirm this. 

The real reason certain groups see purple loosestrife as a threat is that it threatens their sports--angling and hunting, and they have been successful in convincing other conservation groups that the plant is actually a threat to wetlands themselves. According to a past president of the Toronto Field Naturalists, the Ontario Federation of Naturalists have been receiving considerable funding from Ducks Unlimited and they have joined with the anglers & hunters in trying to have loosestrife banned. 

Tom Thomson, a horticulturist acquaintance of mine, has suggested that we form a new organization to oppose hunting--particularly the “pouring” of lead from shot into our rivers and lakes. Naturally, the symbol for this new organization would be purple loosestrife!

I have been defending this plant, and reminding gardeners and others of its good points (excellent for bees and honey making, colourful, does well in a variety of conditions, insect and disease resistant, and has a long blooming period), for over a decade now. In that time I’ve been subjected to criticism and tongue-lashings from government officials, do-gooder (so-called) environmentalists, conservationists, preservationists and poor lowly gardeners who don’t know whom to believe. 

During a spring garden show two years ago I had at least a dozen people comment to me about how harsh some readers of Plant & Garden had been on my comments about purple loosestrife. I replied that I was used to such reactions. The lobby against the poor plant is large and well funded by anglers and hunters, and now to a great extent by government officials, many of whom have been duped into spending our tax dollars on schemes that will help “the cause.”

Those who are genuinely concerned about our plant environment, such as Helen Juhola, newsletter editor and past president of the Toronto Field Naturalists, have thoroughly investigated “alien species” and don’t see them in the same light as many of the anti-alien-plant people. In many cases those concerned about purple loosestrife have only themselves or their predecessors to blame because land has been disturbed and that’s where “the purple demon” is able to come in and take over. 

Those condemning the plant might well check with competent researchers such as Dr. Spencer Barrett of the University of Toronto’s botany department. Dr. Barrett’s Ph.D. dissertation was on invasive alien species. He and his colleagues in that field dare anyone to show a natural, undisturbed pristine environment where purple loosestrife has invaded. He also points out the following. 1) The plant, though a major nuisance, is not causing any great economic loss (except maybe to the anglers and hunters!). 2) There is no data showing that it causes any loss of diversity of species. 3) It does not affect ecosystem health because most of the ecosystems are al-ready disturbed.

It is also interesting to note that University of Guelph zoology department professor Ted Knuds a few years ago released a paper discussing the pros and cons; and it concludes that the threats attributed to purple loosestrife are largely exaggerated, a point I have been making for a full decade. 

Further, I understand that the totally inept and misdirected research project at the University of Guelph that introduced three supposed bio-control insects--two that attacked the foliage, and one the roots--is finally ending because the funding has been cut. (Do we not remember rabbits in Australia and starlings here?) Though the funding has been cut we may well yet face a problem from one or two of these introduced species attacking other unique garden plants!

The negative campaign by so-called environmentalists who would see us--every one of us--going out and ruthlessly pulling out all plants along waterways, roadways and fields, as well as not planting (or not even being allowed to plant) it in our gardens, is actually diminishing--finally. 

The most interesting newer data comes from two studies done at the University of Guelph and completed in late 1997. Each was published in a professional journal, and I recently spent a half-day reviewing the manuscripts in detail. I can tell you at the outset, they are not good news for the do-gooder so-called environmentalists!

The first released appeared in the journal Biodiversity and Conservation 7, issued in September 1998. It’s entitled “The implications of accepting untested hypotheses: a review of the effects of purple loosestrife in North America.” Authors Heather A. Hager and Karen D. McCoy were then at the University of Guelph department of zoology; Heather is now at the University of Regina, department of biology and Karen at l’Université Pierre et Marie Curie, laboratoire d’écologie, Paris, France.

The abstract of their paper reads: “The acceptance of poorly tested hypotheses has adverse scientific consequences, and may have adverse ecological and social consequences. The hypothesis that purple loosestrife has deleterious effects on North American wetlands is an example. We traced the history of purple loosestrife and its control in North America and found little scientific evidence consistent with the hypothesis that purple loosestrife has deleterious effects. The most commonly cited study of the effects of purple loosestrife on native flora and fauna produced inconclusive results. The general acceptance of this hypothesis, however, has resulted in the introduction of non-indigenous insects for biological control. 

“Efforts to control purple loosestrife may be misplaced and may have long-term ecological consequences if loosestrife does not have the impact it is believed to have. The acceptance of this hypothesis using scientific justifications may affect future scientific credibility. Careful evaluation of the precautionary principle is necessary when considering the control of non-indigenous organisms.”

If you have any doubt about this, I would encourage you to read the entire item. 

The second study is perhaps even more interesting. It is entitled “Relationship between the abundance of purple loosestrife and (other) plant species richness along the Bar River, Canada.” Its authors are Michael A. Treberg and Brian C. Husband then both of the department of botany, University of Guelph. Michael is now at the University of British Columbia, department of geography.

The study was carried out along a 2.5 km section of the Bar River, about 30 km east of Sault Ste. Marie, Ontario. This river is described as slow moving and its banks vary from gentle slopes to steep banks of up to two metres in height. The steep banks often collapse into the river, providing new areas for plant colonization. The soil is heavy clay with very little organic matter near the water’s edge and with increasing organic matter content further up the bank. 

The authors point out that they chose the site for a number of reasons, not the least of which were: 1) loosestrife has colonized the river for about 12 years and thus sufficient time has likely passed for the impacts of loosestrife invasion to develop; and 2) the river offers a wide range of densities of purple loosestrife.

Their paper appeared in its entirety in the journal Wetlands, published by The Society of Wetland Scientists (you certainly couldn’t ask for more credibility on this topic than this group!) in March 1999.

Here’s their abstract. “Purple loosestrife is a perennial herbaceous plant that was introduced in the 1800s into North America. Its geographical expansion has generated much concern, in part because its spread may lead to a reduction in the diversity of plant species in wetlands. We tested this hypothesis by examining the association between the abundance of loosestrife and vascular plant species richness in 41 2m2 plots along the Bar River. No significant differences in mean species richness were found between plots with and without loosestrife. For those plots containing loosestrife species richness was not related to the percentage cover of loosestrife. Furthermore, there were no significant differences in the number of introduced plant species be-tween plots with and without loosestrife, nor were there differences with increasing percent cover of loosestrife. [Some] plant species such as [three] Scirpus species were more likely to be found in plots with loosestrife than without. However, no plant species were significantly more likely to be found in plots without loosestrife than with it. 

“Collectively, these results provide no support for the hypothesis that the number of species in wetlands is decreasing in association with the invasion of loosestrife in Ontario.”

Even before they began this significant study, the authors noted that in issue 19 of the journal Environmental Management, professor M.G. Anderson had found, during his review of literature (in 1995), “that studies of competition between loosestrife and other plants are few, but of those conducted in the field, some have shown that loosestrife seedlings cannot compete with native species and that stands of loosestrife were frequently invaded by native species. 

“These results are inconclusive and suggest that the impact of loosestrife in North America may be more complex than was originally suggested.”

This latter observation: stands of loosestrife being invaded by native species is exactly what was observed back almost two decades ago by colleague Fred Dale, gardening columnist for the Toronto Star. Fred’s observations were based on his personal experience along the stream and pond on his own rural farm. If only Fred were alive now to see his and my comments of the time being confirmed by “ivory tower academics!”

Art C. Drysdale, Horticulturist.