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HI Jim & All, Oct 31, 2010
Executive summary:
I can not think of one non-native plant that has caused a serious problem in Eastern Canada. Some, for a few years, may locally overwhelm native plants. But sometimes native plants overwhelm other native plants.
The longer version:
Labels tend to cloud rather than clarify matters, as I will discuss later. First though one should get the history correct.
Based on Gray' s Manual (7 th ed; 1908), Purple loosestrife (as Lythrum salicaria and as L. salicaria var. tomentosum) must have landed in North America way before 1900. By the time this 7 th ed. was compiled and printed, typical PL was present in N.E., Del. & D.C. and var tomentosum was present from e. Que to Vt and in s. Ont. Much of these range descriptions were likely based on pre-1900 collections.
Someone who has access to earlier editions of Gray's manuals and/or Harvard/Yale herbaria catalogues will be able to establish a more precise date but I would guess well before 1800 and perhaps partly or entirely as ornamentals.
The 7th ed. says L. salicaria is 'local'. In the 8th ed. (1950) this is expanded to 'locally abundant, often too aggressive in choking out native vegetation.' .
LABELS: Labels are fine if in, e.g. ecology, if they are used to characterize some set of responses to some defined set of conditions. The label "Old Field Spruce" e.g. has been used to refer to the forest cover that initially replaces the mostly herbaceous ground cover of abandoned farmland; the older trees being predominantly Spruce (favoured by exposed mineral soil) and the later arrivals being predominantly Fir (favoured by litter).
I suppose from the viewpoint of these displaced shade-intolerant herbaceous plants, these Spruce could be considered "Invasive" but more objectively they are just players in a process of secondary succession.
And secondary succession never sleeps. Shortly after crustose lichens establish borders they are swamped by foliose lichens that prosper at the edges and decline in the middle. And comparable processes of encroachment, prosperity at the fringes with stagnation in the interior can be seen in the vegetation of barrens, bogs and even in woodland (esp at the level of air photographs).
But labels, such as "Invasive Alien" that are assigned on the basis of prejudice or labels that have emotional overtones can obstruct clear thought and consequently belong more in the realms of politics or propaganda than in natural history or biology.
In many and perhaps all cases the question is not "Why did this plant become invasive ?" but "Why did it become fashionable to call this plant invasive ?" Or even "Why did it become fashionable to call alien plants that do unusually well here invasive ?"
Was it to drum up support for field research ? [It is unfortunately likely true that a research proposal to avert some crisis is more likely to be funded than a proposal to just study the natural world. If there is no crisis in sight then it will be expedient to invent some. Surviving cultures are those that adopt the trappings that facilitate survival.]
Or was it to solicit contributions to save... whatever fits...; our native pristine wetlands...the Acadian Forest... or at least cover the cost of collecting the contributions ?
Proceeding now from the general to the particular, if we are to " ordinarily rule against importation of any non-native species. " I guess this means we should, while there is still time before these non-native species become vicious, wipe out the Sable Island Ponies and of course outlaw most agricultural crops and livestock ( e.g. horses, cattle, sheep, goats, asparagus, potatoes, oats, barley , wheat, beets, carrots, tomatoes, apple, pear, ....and rabbits; especially rabbits) and, to be on the safe side, we should bring back non-selective herbicides and wipe out the mostly non-native vegetation of lawns, ornamental shrubs and flower gardens.
And if we are going to "ordinarily rule against importation of any non-native species", and bearing in mind that native species are already here and thus do not need to be imported, I guess this means that we should close the border to all trade involving plants (or animals by extension).
Hopefully those non-native plants that travel by wind, water, flesh or fowl will do the right thing and bail out before they cross the border.
But on the other hand, perhaps those very aggressive invasive species will be inconsiderate enough to cross the border anyway. In fact that might be a practical working definition of this class. Therefore, on this basis, all plants should be on the white list.
Yt, Dave Webster, Kentville
----- Original Message -----
From: James W. Wolford
To: NatureNS
Sent: Monday, October 25, 2010 5:25 PM
Subject: [NatureNS] re unauthorized vs. OK plants lists
Randy's example of purple loosestrife is an instructive case in point. As I understand it, p. l. was imported into North America way back in the early 1900s? 1930s? or even before that, but for unknown reasons didn't become a large problem and invasive with detriment to native plants and marshes until several decades passed. My impression from reading is that this is a fairly general phenomenon regarding imported alien species, so that it's difficult to predict which plants will turn out to be invasive. Thus the general principle that all jurisdictions need to, as a rule, untilize precautionary skepticism and ordinarily rule against importation of any non-native species. Cheers? from Jim in Wolfville
Begin forwarded message:
From: Randy Lauff <randy.lauff@gmail.com>
Date: October 25, 2010 9:31:31 AM ADT
To: naturens@chebucto.ns.ca
Subject: Re: [NatureNS] White list of authorized plants
Reply-To: naturens@chebucto.ns.ca
I think the point of a white list, as opposed to a banned list is relatively straight forward, actually.
I do take Marty's point that with huge shipments of goods, and also people who won't abide by rules, control may be difficult. I don't think anyone believes that a "toss in the towel" approach is correct either.
Assume for a moment that Purple Loosestrife was not here, and assume we did not know of its potential invasiveness. It would not have appeared on a banned list. Anyone could have imported it for sale as a garden plant, then boom, we'd have had a problem. If on the other hand we used the white list approach, Loosestrife would not have been on the list (I assume all species on the list undergo some sort of clearance to make it on the list), and Loosestrife would not have been allowed in to the country. Barring accidental import, we would not have had the problem. One can guffaw at this example as being trite, but I'm using it to illustrate a point.
The precautionary approach is being used to p