From Sustainable Landscapes and Gardens: Good Science, Practical Applications, the hot-off-the-presses book edited and co-written by Linda Chalker-Scott, Linda's own chapter on native plants and introductions (never the loaded terms "alien" or "exotic") deserves some attention here on the Rant. That's because as much as we appreciate plant passions, we're also big fans of science, especially when it might just clear the air caused by all those passions.
So I'm quoting extensively in hopes that Linda's unemotional assessment will break through the relentless overgeneralizations about both native and nonnative plants, and bring some civility to the topic. Oh, and maybe reduce the "exotic guilt" about growing, say, hostas or daylilies that we're seeing mentioned with growing frequency. (You want guilt-inducing? Grow up in Richmond, VA hiding your mother's maiden name – Sherman – and your family connection to the Atlanta-burner himself. Then go to college in the North and be held to account for, well, all of Southern history. Interesting times!)
So let's starting with definition of "native". According to Linda, that here-before-the-Europeans thing isn't as clear-cut as we think. For example, the Ginkgo biloba is considered an Asian plant, yet its fossils can be found in Washington State, where it grew millions of years ago. Concludes the good hort doctor: "Defining a plant as native based on what existed in a landscape before European immigration ignores the influence that earlier human cultures, animals, natural forces, and natural selection have on plant introductions and distribution." And " This is not a rational approach to understanding the dynamic character of landscapes either in natural or urban areas."
Benefits and Drawbacks of Native Plants (Ever seen that header before?)
She lists the well-known benefits (see any source on the subject), but also the missing caveats in almost all discussions of native plants: "Unfortunately, many of us live in areas that no longer resemble the native landscapes that preceded development…The combination of urban soil problems, increased heat load, reduced water, and other stresses mean that many native species do not survive in urban landscapes. … When site conditions are such that many native plants are unsuitable, the choice is either to have a restricted plant palette of natives or expand the palette by including nonnative species."
Landscape Uses for Native Plants
For parks and public areas that are minimally managed, Chalker-Scott recommends selecting natives that "are easily planted and require little care once established." Not just any native plant.
And in developed areas: "Commercial and industrial sites and planting strips along streets and highways receive little to no care and are usually environmentally hostile and unsuitable for many natives. In addition to the typical problems associated with urban environments, these areas may be overrun with nonnative, invasive plant species, contaminated with pesticides and other pollutants, and contain small root zones with little available water or nutrition. So few native species can tolerate these conditions that we must consider supplementing our plant palette with better adapted, nonnative species."
Benefits of Introduced Plants (Again, ever seen that?) Italics added.
- "There are practical, functional, ecological, and aesthetic reasons for using introduced species. From a practical standpoint, you may not be able to find many native plant species at your local nursery. If you limit yourself to a sparse selection, you decrease the potential biodiversity of your landscape."
- "Introduced plants can provide functions that perhaps native species are unable to do in your landscape of interest." Functions like removing pollutants from the soil, or fixing nitrogen, as clover does. "The nature of many urban sites is such that native plants are unable to establish and survive", and nonnatives have proven in many cases to provide these functions, including providing for wildlife.
- "Similarly, native species that are locally extinct can be replaced by nonnative members of the same genus and thus increase the biodiversity of the landscape."
- "Finally, there are the aesthetic benefits of broadening your plant palette. Though it may seem less important from a scientific standpoint, in fact studies have shown that attractive landscapes can improve human health and well-being, to the extent that healing gardens are now common in many medical facilities." (And can I add – aesthetic benefits often mean turning homeowners into passionate gardeners like me who've filled their yards with environmentally beneficial and sustainable plants.)
Drawbacks of Introduced Plants
Here she lists again the usual warnings, starting with the chance of invasiveness. There's also the chance that imports could contain nonnative pests, parasites, or disease – stowaways – an outcome she calls unlikely because of quarantine and inspection by the USDA.
The last drawback is the possibility that the introduced plant doesn't have genetic resistance to local pests and diseases. That's one more reason reason to avoid buying brand new introductions – whether imports or hybrids or whatnot. Because you never know – the latest and greatest could turn out to be another Windows Millennium Edition.
Click here for info about the book and how to order.