Invasive species

Jane McGary
Sun, 02 Aug 2009 09:50:42 PDT
Jim Waddick posted a list of  "100 of the World's Worst Invasive 
Alien Species"
>according to the IUCN's Invasive Species Specialist Group reported at:

Jim asked us to comment on which ones are grown in gardens and sold 
in our areas. Of the 32 species listed, I count 22 that would not 
survive in the open here because they are not cold-hardy and/or 
moisture-tolerant; 4 that are in the trade and occasionally grown 
(Imperata cylindrica, Pinus pinaster, privet,. and tamarisk), but not 
invasive owing to climate incompatibility; 3 that are both invasive 
and cultivated (Arundo donax, sold by "water garden" nurseries; 
Fallopia japonica, sold in a variegated form as an ornamental, 
although state listed as a banned plant; and Lythrum salicaria, sold 
in purportedly but not actually sterile clones, mostly by mass-market 
nurseries headquartered in the eastern or midwestern USA); and 2 
(spurge and gorse) that are weeds spread by livestock and agriculture 
and never cultivated. I don't know what a yellow raspberry is, but 
other species of Rubus, introduced by agriculture, are serious pests 
here (so is the native Rubus ursinus, where found on land desired for 
human activity).

The only one I've ever had in the garden is Lythrum salicaria, and I 
didn't let it get loose.

The list consists mainly of tropical and subtropical species. In 
western North America, many invasive species are of Mediterranean 
origin. In addition, overgrazing can cause a native species to become 
"invasive" and change the entire ecological balance, as has happened 
in the arid West with mesquite and western juniper (Juniperus occidentalis).

It's obvious that control of invasive species isn't something that 
can be approached on a single basis for a whole continent. In my 
area, for example, ivy (Hedera helix) is a serious problem, but 
ornamental clones can still be sold, which is ridiculous; I confess, 
however, to growing a variegated "needlepoint" miniature ivy for use 
in flower arranging (it has never fruited in more than 20 years). Yet 
no doubt there are parts of North America (e.g., Colorado?) where ivy 
doesn't threaten native vegetation. Scotch broom (spread mostly by 
logging activity) is an awful problem around here, but there are 
plenty of cultivars on the market elsewhere in the USA, and although 
claims are made that these will not become invasive, that is not 
true. Invasiveness can be very localized; for example, Crocosmia is 
invasive right along the Pacific coast, but one never sees feral 
plants east of the Coast Ranges, as far as I know.

On the other hand, you can't ban a plant in one region and hope to 
keep it out if it's being offered in nursery catalogs from other 
parts of the country. (The "cannot be shipped to California and 
Oregon" notices you see have to do with pests, such as Japanese 
beetle, hosted by the plants or the soil they may be grown in, not 
invasiveness.) More ethical behavior on the part of growers is one 
crucial part of solving this problem, just as better practices by 
farmers and, especially, livestock ranchers are crucial.

Jane McGary
Northwestern Oregon, USA

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