I was recently asked what defines a native plant, a question best answered I think, by two characteristics, geography and time.
Geographically, we can say a plant is native to North America, or to the eastern US, or the coastal hardwood forests of New England, or Middlesex County. At the fussiest level, it would be a genetic type specific to a small location, as small as five square miles. This last level of “native” is most important for plant restoration projects where there are large altitude differences or water issues, as that is the place where evolution has given specific genotypes the ability to survive a hostile environment. This final distinction is not important for urban/suburban gardeners.
On a temporal basis, things get murkier. In North America, the big division happened five hundred years ago, with the transition from pre-Columbian to post-Columbian society, when Europeans started moving plants from around the world to our shores.
Ten thousand years before that was the last ice age, where glaciers scrubbed New England clean of many plants that existed before the glaciers. Many of those plants remained alive in the southeast beyond the reaches of the Laurentide Ice Sheet. These remnant plants, once native to the northeast, still live in many parts of the southeastern US. The retreat of the glaciers allows them to again be grown here. My favorite examples of these botanical remnants include the Franklinia and the many North American azaleas. Gardeners bring them back north at a faster pace than nature will cause them to migrate naturally.
Our current situation includes human-induced global climate change, which will bring warmer temperatures and less predictable precipitation to New England. The practical implications of climate change on our plant populations are enormous. Big and long-lived species like trees don’t move rapidly in response to climate changes. They don’t have the legs or wings that give animals and insects the power to avoid weather they don’t like, or find the food they need. Our trees take years to reach reproductive maturity. We are likely to lose some of the tree species that are living here at the southern-most parts of their range, including the sugar maple, because they won’t be able to handle increasingly warmer temperatures. On the other hand, southern trees that are marginally hardy here now, because they can barely handle our current cold winters, may become more prevalent with warmer winters. Will we import the trees that take years or decades to migrate naturally to replace the species that we are quickly killing because of our addiction to fossil fuels?
My approach as a gardener to the question about natives is a bit haphazard but there is no religion or purity involved. I do grow a lot of non-natives but I am growing more plants that are native to the range that I consider the eastern deciduous hardwood forests of northern America, and their associated open spaces. I am using fewer named cultivars. I try to get plants of the same species from different sources so I don’t increase genetic in-breeding. Yet I am gradually bringing in plants that thirty years ago could not have survived our cold winters. Two paw-paws that are at the northern edge of their historic range are now thriving after years of struggling against the weather. My tiny back yard hosts salamanders, hummingbirds, Orioles and spicebush swallow tail butterflies, all formerly ubiquitous in Arlington but rare today.
I am now a grand-father to a sixteen month old. Issues like these that were once big, global and important have become very small and even more important to me.
I want to plant more sourwoods (Oxydendron), the native smokebush (Cotinus obovatus) and my first ever tulip poplars (Liriodendron tulipfera). I want to see them instead of the contemptible Norway maple when I look across the landscape. I want Nina to know what it is like to smell a real garden, a real plant, to see flowers and birds that will make her shout. I want her to pick a native blueberry, a native raspberry, a paw-paw and see her put it in her mouth and smile.