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The precautionary approach is being used to p
David & Alison Webster wrote:
> 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.
* there's a lot of good points here, but I think the questions relevant
to the executive summary are "how far west does eastern Canada extend,"
and "what constitutes a problem."
If Toronto is allowed to be part of "eastern Canada," then between
European Phragmites, Norway Maple, Goutweed, Dog-strangling vine,
Flowering Rush, Pink Jewelweed, Buckthorns, Narrowleaf Cattail, Garlic
Mustard, and a host of other alien plants, there's not much doubt that
even forests and other "natural" habitats have had their native species
considerably diluted, and one can't say how much truer this would be if
Purple Loosestrife and Saint Johnswort hadn't been knocked out by
biological controls. I described the alienness of the Toronto area in
http://groups.google.com/group/naturelist/msg/661b4fcb53862d34?hl=en.
When I commented to Bev Wigney this summer about the relatively native
vegetation in Nova Scotia, she promptly reminded me of a lot of alien
species that were all over the place, but that weren't on my Ontario
alarm list (her homesite is equally divided among two alien species of
Cherries and Black Locust, with wide patches of Goutweed, Dame's Rocket
in the woods, and Celandine scarce only because she'd been pulling it
all summer)
http://karstaddailypaintings.blogspot.com/2010/09/old-black-locust.html#more
There's three kinds of problem that alien plants can cause, first is the
direct squeezing out of native species of plants by competition. The
second is the redirection of the photosynthate they produce into their
own growth and away from Insect herbivores, and direct attributes of the
native species that might otherwise feed or benefit native animals.
The third is more abstract: the dilution of the biogeographic integrity
of the biota. If one accepts maintaining as much as possible of the
biogeographic differences among places as a proper goal of People who
live on the Earth, then the dilution of native species is an absolute
harm that's done by all alien species, including ourselves, against
which any human action that may introduce new species must be balanced.
But of course biogeographic integrity is not a widely endorsed as a
motivation, and its maintenance is derided as an overt motivation even
by some invasive species biologists.
The thing about invasive species is that they're such magnificent Plants
that struggling against them in an open-minded way teaches the clear
lesson of the importance of loving your enemies.
fred schueler.
============================================================
> 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 o