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Sunday, July 24, 2016

Invasives are here to stay

I hate to say this, because I think it will make some people mad, but I don’t think there’s any hope we can eradicate invasive nonnative plants from our landscape.

    This is an area of hot controversy. Many admirable volunteers spend their weekends pulling out invasive plants that grow on public land. 

Volunteer at a garlic mustard pull in Washington state

These are plants that cause environmental damage, out-competing natives and endangering local insects and animals because they don’t provide them with food and shelter they need.

    People who devote their time to eradicating invasives reject tolerating these plants. But there is another perspective. As Hope Jahren points out in Lab Girl, “Humans are actively creating a world where only weeds can live and then feigning shock and outrage upon finding so many.” Cities are hotter, dryer and windier than the countryside they replace, and we keep tearing up the ground with new building projects. No wonder only the toughest plants survive.

    Even if public land were cleansed of invasives, it doesn’t exist in a vacuum. At the Garden Bloggers Fling in Minneapolis, I heard that the Eloise Butler Wildflower Garden  had to have volunteers scour garlic mustard (
Alliaria petiolata) from a buffer zone around the 15-acre garden to keep it from migrating into the reserve. Yet every year their staff still has to patrol the property for garlic mustard seedlings. 

Native black-eyed Susans and bee balm at Eloise Butler Wildflower Garden

    Garlic mustard crowds out other herbaceous plants and excretes antifungal chemicals that disrupt connections between soil fungi and native plants, suppressing growth. 

Garlic mustard in bloom

What is the chance that every Newton homeowner will police her property and catch every garlic mustard plant before it sets seed? Not since Maoist China has social engineering on that scale been feasible.

    Here’s a case in point. Across the street from my house, a neighbor’s fence runs parallel to the sidewalk. In the few inches of soil between the fence and the pavement, a panoply of invasives has taken root. There’s garlic mustard, Oriental bittersweet (
Celastrus orbiculatus), Norway maple (Acer platanoides), and black swallowwort (Cynanchum louiseae). Yes, I uproot them as I walk by. But all over town the same situation is occurring, and in most places no one notices or cares.

Oriental bittersweet

Norway maple
Black swallowwort
So if we can’t kill all the invasives, what are we supposed to do? Are we willing to let them take over and accept simplified landscapes without the biodiversity needed to maintain native animals? 

Actually we already have. A stroll in any local park confirms the presence of large populations of invasives. 
     I may be unrealistic, but I prefer to think that by planting natives in our own yards and fostering their growth on public lands, we can restore some balance between natives and aggressive nonnatives. If not, we’re going to spend all our gardening time at war, and that’s a condition I can’t accept.

Native red oak in my yard. This is a popular host plant for native insects

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