Critical to an understanding of the importance of native plants is knowing just what we mean by that word “native.” It is a word with variable meanings, and how it is used in describing plants does not match how we use it in reference to human beings. This confusion can erode support for control of non-native species, for to some it is a distinction equated with “immigrant-bashing.”
First, the basic meaning when used with humans:
To be native is to have been born in the area in question; but native also designates those whose ancestors were from the area, particularly if the culture has become especially adapted to local conditions over many centuries.
Immediately, we have two levels of meaning, and we’re only talking about humankind. I am a native American, but not a Native American. Human mobility adds other problems. I was born in Washington, for example, but grew up in California. How can I be a native of Washington when I hardly know the place—yet I’m not a native Californian, either!
To clearly communicate, we must understand the underlying reason for using the label. In human beings, “native” may imply respect for a culture which has been shaped by sustainable interaction with a particular ecosystem. Or, if we are bigots, we may use it with derision for “ignorant savages” who know little of the outside world and modern technology. Often we imply territorial rights. Native people were here first, therefore they have rights not automatically due to newcomers.
Note how in that territorial sense, we tend to emphasize the meaning of the word which justifies our politics. This becomes particularly strange when here in the Southwest Americans of Northern European descent complain about all of the trouble caused by “illegal immigrants” from Mexico—when their own ancestors weren’t invited to this region by the descendents of Spanish explorers who settled in New Mexico four centuries ago. Nor were the Spanish invited by the Navajo or Apache, nor the Navajo and Apache by the Hopi before them. If we live in an area and want to stay there, we tend to feel just as native as someone whose ancestors pre-dated us by many centuries.
But territorial rights are all political concerns, questions of relations among the members of our own species. I suspect most scientists understand that this association of the word native is too subjective. To be useful when speaking of native plants and animals, it must have meaning in the context of the sciences, particularly ecology and evolutionary biology.
This is why a native plant species is best defined as one which has inhabited a particular region for thousands of years.
It takes thousands of years for the species of an area to co-evolve, to adapt to each other and to the peculiarities of their physical environment. This is why a plant species which has survived in the area for a few decades or even a couple of centuries isn’t considered to be native.
An Arizona Native Plant Society field trip participant seemed puzzled—if not a bit put off—when I mentioned that mullein (Verbascum thapsus) was an alien species. She had heard that the Navajo used it. If a Native American uses a plant, is it not then a native plant? No, because we are mixing two different senses of the word. Any intelligent land-based culture, like that of the traditional Navajo, will make use of any plant new to the area if it can be used. Likewise, I’ve observed native Lesser Goldfinches eating seeds of the alien and rapidly spreading star thistles—but that does not make the star thistle native.
So be careful about associating political issues on human immigration with ecological issues on controlling alien plants. Believing the US should open its borders to more immigrants but at the same time being dead set against importing alien plants is not inconsistency. If, on the other hand, you feel that our government should expel all undocumented immigrant people and stop any others from entering, it does not follow that you should also take a “native plants only” stance. These are completely different issues.
The reason they are different is the dominance of culture in humans. In short, a human being can change behavior to minimize impact on the new home. A plant cannot (not without thousands of years of evolution).
Can an immigrant plant ever become native—in the biological sense? Yes, after thousands of years. No one can give a precise time, for the moment a plant enters new territory, the forces of evolution begin: any time the new environment (including, remember, animals and other plants) favors one genetic trait of the newcomer over another, natural selection begins. I would expect that after even just a few hundred years, some species (particularly insects and other invertebrates with short life-cycles) would adapt to the presence of a newcomer, for a food-source (i.e. any other organism) will not go forever unused.
To get an idea of the relative speed of evolution, consider creosote bush (Larrea tridentata). This species found it’s way to the southwestern deserts just around 10,000 years ago, apparently from South America where a close relative exists today. It is the dominant shrub now in this “new” home. There are now numerous species of insects and spiders associated exclusively with it (and not found in South America)—all evidently having evolved in that time frame. I don’t think anyone would disagree that creosote bush is now a native species.
But since any species reproducing in a region is eventually going to become native after (I repeat) several thousands of years, should we bother trying to control or eliminate alien plants? Yes, if we care about preserving native species, whether plant or animal. And yes, if we care about our own survival.
The key concepts are these:
1) Change is always present, to a greater or lesser extent. Never mind the actions of humanity, continents move, earthquakes occur with the shifting of continents, volcanoes erupt, mountains are raised and eroded to the ocean, climates change, plants and animals naturally migrate to wherever they can survive.
2) Rapid change causes extinctions. Most multi-cellular species cannot evolve fast enough to cope with rapid changes.
3) The more change, the more difficult it is for organisms to adapt and survive; i.e. the number of changes matter, in addition to the rate of change.
4) The introduction of an organism into a particular region is itself a change. Neither animals nor plants are inert. Their very presence will have an effect on the biotic community. Ways plants may affect the environment include competition for resources (space, water, nutrients, light); competition for pollinators; change in the chemical composition of the soil from root secretions or the decay of leaves; attraction of animals (including invertebrates) to the area which might not otherwise live there.
5) The more rapidly new species inhabit a region, the more unstable is the composition of the flora and fauna of that region—not merely because a new species, by definition, changes the flora or fauna, but because the new species itself can cause changes in the abundance of existing species for the reasons suggested in 4) above.
6) Our survival is directly impacted if among the species which become more abundant as a result of widespread environmental change are very many which crowd out our food plants (“weeds”) or eat them outright (“pests”). Changes in plant cover can also change the local and even global climates, and this may have far-reaching economic effects in our lives, such as less predictable and more adverse precipitation and temperatures. And to the extent that these changes, in concert with the pressures of human overpopulation and increasing demand on resources, cause economic hardships, we increase the number of people who feel they have nothing to lose by violence, by the adoption of fanatical and intolerant world views. Preserving stable native ecosystems is, in other words, one key part of preserving the relatively stable economic and political systems we depend upon.
It therefore is prudent for our own survival on this planet that we attempt to minimize changes in the native ecosystems which, by definition, have evolved a high degree of stability. Things will change, whether we will or no. But we can limit the rapidity of change.
We have already made enormous alterations to much of the country, and the world. We need to cut our losses by, a) halting or slowing the spread of alien species, b) revegetating impacted areas with locally native plants, and c) adopting an attitude and philosophy of enjoying what each local native ecosystem has to offer rather than trying to “improve” it by bringing in plants from other parts of the world.
So the meaning of native in ecology is identified with stability. A native ecosystem is a tried and true community.
Can we reconcile the variable application of the term native as used with human beings to that used with plants? Yes, if we invent the concept of “functional nativity.” A plant is native if it has co-evolved with its associates for thousands of years. We hominids can be functionally native if we behave as if we had co-evolved with the plants and animals of the region wherein we choose to dwell. This means using our intelligence, coupled with science, and in consultation with the traditions of native cultures, to practice a sustainable way of life—one quite different from our present “buy your way to happiness” short-sighted culture.
With such a practice, it matters not in the human realm whether our ancestors were here for millenia or are just two days off the plane from Finland or South Africa. To be functionally native is to be in tune with the patterns and needs of the amazing native biotic community—wherever we live.
This article first appeared in the Late Winter 2002 issue of Townsendia, the newsletter of the Northern Chapter of Arizona Native Plant Society. It has been slightly modified here. This page last revised 16 April 2009.
|Northern Arizona Flora|
|Ferns and Fern Allies||Gymnosperms||Angiosperms: Dicots||Angiosperms: Monocots|
You can help support the development and maintenance of NAZ Flora by purchases from www.mindbird.com, the Mindbird Maps & Books retail website.
See the selection of hand lenses, field guides and floras, maps, and much more of interest to the nature lover or biological sciences professional.