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Sunday, May 24, 2015

This means war

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). 
Oriental bittersweet coiled to spring
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.
            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 na├»ve 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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