The difference between continental, regional, local

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Bringing up the topic of native/exotic plants in a conversation with a group of otherwise sane, considerate, and law-abiding citizens is a bit like blocking a continental storm in a planet-sized teapot — a full-fledged, super-sized cage match where sophisticated women in noble Pearls and dapper men in starched blue blazers and no-frills pants smack chairs down each other’s backs, eventually finding themselves in unyielding sweat boxes that refuse to yell “uncle.”

In Part 1 of this series, we spent a lot of time trying to understand exactly what a native plant is, or more importantly, how difficult it is to come up with a static, unified definition of the term. About as close as we could get is that a plant is generally considered native to an area if it has gotten there largely with little to no human intervention.

(Please wait a few minutes with the headlock – I said that’s a pretty general definition. Before you unleash the pro wrestling moves, give me a few more paragraphs.)

And of course, it’s pretty simple that once you’ve defined “native,” anything that doesn’t fit that definition must be exotic. A plant that grows in a particular location is either native or exotic… at least for our discussion so far.

And then there’s the term “invasive” (and this is where the headlock activity starts to get really ugly.) An invasive plant is generally defined as a plant species that is not native to the ecosystem in question and is spreading for economic or ecological reasons cause damage to this area. And that means plants like the much-maligned Asia-native kudzu (Pueraria montana var triloba) and Amur honeysuckle (Lonicera maackii) are clearly exotic and quite clearly meet the definition of invasive plant species, plant species native to one part of North America may indeed be considered invasive exotics in another part of North America if they meet the wording of the definition.

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And of course we have exported some of our own North American native plants abroad to become invasive exotics in other countries.

This is not a one-way street.

Why exotic plants can wreak havoc on the local ecosystem

There is no debate that the influx of some exotic species into the US costs us enormous amounts of money, economic productivity and ecological damage each year. The cumulative total of economic losses from invasive exotic species (plants, animals, pathogens, etc.) in the United States exceeds $100 billion annually, affecting more than 100 million acres of land. Globally, the annual economic impact of invasive exotics equates to a whopping 5% of the entire global economy.

Enter the aforementioned Amur honeysuckle (Lonicera maackii), a plant introduced to great acclaim in 1898 by the US Department of Agriculture for purposes of conservation planting (soil stabilization and fruit production for wildlife) and the garden and landscape trade. It is an attractive plant with beautiful white/yellow, fragrant spring flowers and cherry red autumn fruit. It supplies truckloads of food for winter birds. And it’s incredibly adaptable and easy to grow.

But because of Amur honeysuckle’s unique adaptability, it overgrows fully forested and open areas in some parts of the US, where it forms gigantic monocultures. The decline in plant diversity then leads to reduced animal diversity and an overall decline in ecosystem resilience/health.

And it’s hard to kill.

Japanese stilt grass is another invasive plant species. Ellen Jacquart |  courtesy photo

Other “introductions” of exotic plants have not been done on purpose but by unfortunate coincidence. Japanese stilt grass (Microstegium vimineum) is listed as one of the most noxious invasive exotic plants in the United States by the USDA National Invasive Species Information Center. This annual grass spreads rapidly by seed, where it crowds out other existing vegetation and greatly reduces plant and animal biodiversity. But this distant native was not introduced on purpose. It was hitchhiking with packaging material that came to the United States from China.

But as harmful as some invasive exotic plants can be, the introduction of new plant species to our country has also brought some significant, even civilization-altering, benefits. Corn, wheat, potatoes and cotton are all imported from other countries and have become a central part of our daily lives.

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What is the difference between ornamental and native plants?

Like all plants, the locally native flowering dogwood (Cornus florida) varies slightly across its native range.  A plant from one part of a plant's native range may not do well in another part of the range.

Now, one term we haven’t discussed yet is ornamental.

As gardeners and homeowners, we often look for a plant that will look good – decorative – in the yard or garden.

But for some unfortunate and annoying reason, the term “ornamental” is often used as the opposite or counterpart of the term “native.” It’s as if someone decided decades ago that native plants cannot be ornamental and ornamental plants cannot be native.

I don’t know about you, but our flowering dogwood (Cornus Florida) strikes me as terribly ornamental, as does Virginia bluebells (Mertensia Virginiana) and American beech (Fagus grandifolia). And as invasive and destructive as the Amur honeysuckle is across much of the American landscape, it’s actually quite decorative.

So, in the interest of civil and productive discourse, let’s clean up the native vs ornament thing and stick to distinctions that help us move the needle to a better and more meaningful conversation.

Why we need to include ecology in plant growth and success

Finally, in our search for a common and useful vocabulary around our discussion between natives and exotics, we need to go beyond geography and talk a little about ecology.

They see as much as we like, plants just don’t read maps. They tend to grow and thrive where they are most competitive – where soil texture and fertility, as well as light and moisture conditions best suit their needs, and where they can find a niche in which they do better than others. And it’s extremely helpful for us to keep this in mind when discussing a plant’s native range.

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The flowers of the Amur honeysuckle (Lonicera maackii) make an attractive spring show and the fall fruits are showy and excellent food for birds.  But this exotic plant is a destructive invasive plant that crowds out existing vegetation, resulting in reduced biodiversity.

A plant native to Jefferson County, Kentucky isn’t necessarily a good choice for every square inch of the county. A silver maple growing on the wet and occasionally flooded banks of the Ohio River isn’t necessarily a good choice for a dry ridge in close proximity.

So to help us make decisions about what to plant and why, the following distinctions I find useful.

What is a continental native plant?

This is the broadest term for native/exotic plants. It simply refers to plants native to somewhere on our continent. That doesn’t necessarily mean that they are all suitable for planting in your garden. And as much as I’d love to grow a big old saguaro cactus (Carnegiea gigantea) in the middle of my front yard, I have serious concerns about its potential to survive for more than 30 minutes on a February day in Kentucky.

But at least the term gives us a way to differentiate between those native to North America and those native to Australia. If you’re trying to build a garden using plants that are commonly considered native to North America, this is the definition of your choice.

What is a regional native plant?

Here, too, no political borders, but meaningful ecological regions. I think we can all agree that far eastern Kentucky is very different ecologically than the central and western parts of the state. The terrain is more mountainous and the soils are much more acidic. So, by evaluating according to regional, ecological criteria, we can start to adapt plants to the conditions instead of simply dividing them up according to other arbitrary means.

If you choose to garden with regional locals, look within reasonable distance for plants with similar growing conditions to your location. Most ecologists would consider something in the near 90-mile radius for the region’s natives.

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What is a native plant?

Asclepias tuberosa - Butterfly Milkweed: The cheerful orange flowers of this Kentucky native plant are common in open fields and roadsides throughout the Commonwealth.  Butterfly spurge is the most popular spurge for sunny gardens.

Here we encounter the finest level of detail. If you work at a local native garden or want to get involved in an ecological restoration, you may be most interested in using plants that are locally sourced – not just locally grown/produced, but propagated through local genetics. Since the butterfly spurge (Asklepias tuberosa) has a very wide native range across much of eastern North America, you may not want plants that come from a source in Wisconsin or Virginia. If you are concerned about using locally sourced plants – local genetics – you should look at locally sourced material.

With the three distinctions above, it is important to remember that all three are appropriate for their own purposes. If you are into a detailed, ecological restoration and only want to use local genetics, great. If you simply want a garden with plants that look like you see them growing naturally in the woods around your home, that’s fine too. No direction is inherently better.

Growing California poppies in Kentucky won’t make you a sinner, and growing Trillium just around the corner won’t make you a saint. The key is simply deciding which approach is right for your own situation.

If you don’t mind, would you please loosen the headlock!

Paul Cappiello is Managing Director of Yew Dell Botanical Gardens, 6220 Old Lagrange Road, yewdellgardens.org.

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