Wild urban plants and our climate future

Peter Del Tredice – a friend of this blog – has published new book, excerpted in Natural History in March 2010: As many scientists have pointed out, modern climate change can be viewed as a massive, uncontrolled experiment on the impact of increased atmospheric carbon dioxide (CO2) concentrations on Earth’s ecosystem. Most people now realize that after more than two hundred years of heavy burning of fossil fuels, every corner of the globe will be affected, but impact at the local level remains unpredictable. And this is where the cities come in: they have already arrived at the future in terms of experiencing higher concentrations of CO2 than the surrounding countryside. Plants in general thrive under such conditions, and because they also serve as a means for carbon sequestration, there is considerable enthusiasm for planting trees in urban areas.

Considering that they grow on marginal sites and require no maintenance, spontaneous urban plants are providing a greater return in terms of carbon sequestration per maintenance dollar spent than most intentionally cultivated species.

As every sufferer of hay fever knows all too well, however, plants do not always enhance the quality of life for the human inhabitants of cities. If recent research is any guide, climate change could well make some of those negative interactions worse than they currently are. Controlled experiments with two infamous native plants—ragweed and poison ivy—have shown that elevated levels of CO2 induce the former to produce significantly more of its highly allergenic pollen and cause the latter to produce higher concentrations of its rash-producing toxins. While such observations do not bode well for humans in a CO2-rich future, they are a reminder of the innate capacity of “weeds” to capitalize on—and often, thankfully, remediate—the mess we have made of the planet.

…Over the next few decades, humans can be counted on to pump more CO2 into the atmosphere and generate more chemicals to pollute the water and the soil. The worldwide migration of people from the countryside into cities is also contributing to environmental degradation because land that was once covered with vegetation is being covered instead by buildings and pavement. The confluence of climate change and urbanization— acting in concert with the global spread of invasive species—has set the stage for spontaneous vegetation to play a major ecological role in the future. These plants are well adapted to the world we have created and so are neither good nor bad—they are us.