Like the war on cancer and the war on
drugs, our relationship with nonnative invasive plants always seems to be
framed as a war. When something invades,
we fight back. Pulling garlic mustard, we’re like heroic patriots battling a
force that wants to wipe out our way of life.
I
can get behind that attitude to some of the invasives I’ve encountered (done
battle with?), such as Oriental bittersweet (Celastrus orbiculatus) and Japanese knotweed (Fallopia japonica).
We invest enemies with almost supernatural malevolent
powers: bittersweet can grow twelve feet in a year (it seems like six inches in
a day, doesn’t it?), girdle a full-grown tree and kill it. To eradicate
knotweed, you have to excavate to a depth of three feet, sift the removed soil
for root fragments, and burn them. I don’t deny that invasive imports have
damaged large areas of farm land and wildlife habitat.
Oriental bittersweet coiled to spring |
A
change of perspective can make the adaptability of invasive plants almost
admirable. Toby Hemenway points out in Gaia’s Garden that a lot of these
plants, ones he prefers to call opportunistic species, pioneer in areas where
humans have disturbed the ground. There’s an example downhill from the parking
lot I use at work. An international mix of tough, enterprising plants populates
the steep slope between the low end of the paved lot and an apartment building
below. Several Norway maples make up the canopy, along with one pignut hickory,
a native tree at the edge of a neighborhood colony. Underneath are aggressive
imports from Europe and Asia: garlic mustard,
mugwort, common burdock, chicory, common lambsquarters, and fall dandelion.
Familiar natives also hold their own: New England aster, sticktight, and
pokeweed. I have to respect the resilient individuals that grow together to
make up that little ecosystem. They’re not daunted by the slope, the run-off of
road salt from the parking lot, the poor soil, the car exhaust, the flooding
when it rains and drought when it doesn’t. When human activity created a
wasteland, these pioneers were ready to move in.
We
need a way to live with globalization and yet keep what’s unique about our
place and community. No one wants all stores to be big box chains or all plant
life to be replaced by a short list of internationally successful aggressive
growers. At the same time, it’s naïve and possibly xenophobic to think that
before European contact (invasion?), North America was covered with a stable
plant community that would have gone on unchanged if we hadn’t brought in nonnatives.
Ecosystems change over time. Now humans have become one of the most powerful
evolutionary forces. Hot, paved cities offer different growing conditions than
the ones that were present before they were built, leading to the rise of what
Peter del Tredici calls “spontaneous urban vegetation.” Try as we might, we
can’t get the genie back in the bottle by restoring native vegetation
everywhere. We’re going to have to adapt to the new reality. I don’t have the
solution to this problem, but I hope one thing we can do in suburbs and cities
is to plant trees. Not all, but many pioneer species can be shaded out by
mature trees—if bittersweet doesn’t kill the trees first. We could sequester a
lot of carbon while we’re at it.
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