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"

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