Fwd: Establishing taxa as "present"
Jane McGary (Tue, 02 Sep 2008 11:44:19 PDT)

Correct me if I'm wrong, but my understanding is that a plant is declared
"invasive" in tests if it spreads by self-sowing or rapid root extension in
a test plot at, for instance, an agricultural experiment station. This may
be applicable to agricultural situations, but it does not necessarily
reflect a plant species' potential to affect indigenous vegetation. Indeed,
native plants can become "invasive threats" when human activity alters the
balance of nature; for instance, juniper has become dominant in eastern
Oregon as a result of cattle grazing, leading to degraded pasture and
increased fire danger.

Every gardener knows that there are many plants we grow that will self-sow
into disturbed soil, but not into fully vegetated sites. For instance, when
the acreage next to mine was being run as a Christmas tree farm, with
herbicide applied between the rows of trees and the soil constantly
disturbed by harvesting and replanting, some of my trees and shrubs seeded
in there, such as birches and buddleia. The farm has now been abandoned for
about 10 years and the trees have grown up closely, and native vegetation
covers the ground between them, and no new self-sowing is apparently taking
place.

On my own acreage, the only species I've seen escape from the garden into
undisturbed soil is a borage, Pentaglottis sempervirens, which was sold to
me as Brunnera by a small local nursery -- when I was new here and didn't
know what Brunnera looked like. I spray it every spring but it is difficult
to eradicate; fortunately, its seeds are large and heavy and don't get far.
(It's pretty in both foliage and flower. Last year Steve Doonan wanted a
start of it, and I had to refuse flatly!)

The answer to preserving native biota is to preserve entire communities, as
large as possible, isolating them from human activity as much as possible
-- not to forbid the growing of rare species of Dionysia in alpine houses.
I suppose there are cliffs in Nevada where the dionysias would be invasive,
though! Indeed, there are probably habitats somewhere in the United States
where almost any plant from anywhere in the world could take hold, from the
tundra of Point Barrow to the swamps of Louisiana.

Jane McGary
Northwestern Oregon, USA