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| Palo Verde tree, native to southern Arizona |
I don't know any gardeners that have only native plants in their yards or gardens, although there are gardeners probably striving to grow only natives. But defining what we mean by native is challenging.
Many gardeners accept only indigenous plants as native
. Gray's Anatomy of Botany says that to be indigenous there must be scientific evidence that the species has inhabited an area for a great length of time, that it's an integral part of local, evolutionary relationships with other plants and animals.
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| Saguaro cactus, native to southern Arizona |
But what is a great length of time? Thousands of years? Hundreds of years? For example, there were plants that were present in an area of the globe before a glacial period, different plants that were present during a glacial period and different plants after a glacial period. Can all be considered native? When European colonists arrived in the Americas hundreds of years ago and introduced species that live on unassisted today, are these species considered native? If a plant has become naturalized as a member of the wild flora, needing no human assistance in self-perpetuating, can that plant then be called native? What of an indigenous plant that migrates to a new area and becomes naturalized without assistance? Is native a function of
time and
place?
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| Lantana, not native to southern Arizona |
Situations like this occur all over the world. If native status is a function not only of time but also of place, defining place can be a perplexing. There can be dramatic differences in habitat within a relatively small area. In my own state of Arizona, within a twenty mile distance, you can go from desert habitat to tundra. And the plants in the tundra habitat in Arizona are the same as the plants in the tundra of Alaska.
And consider what we call invasive plants. They would not exist unless they were better adapted to current conditions than so-called native species. As Richard Darke says in the book
The New American Landscape, " ...most natives are no more than earlier arrivals that established themselves because, at the time, they had a competitive advantage."
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| gazania, not native to southern Arizona |
Non-native plants fulfill roles that can't be accomplished by natives. Many food plants grown in North American gardens do not have their origins here. Many flowers that gardeners grow are not indigenous to their area, but provide beauty, fragrance, color and pleasure, such as the lantana and gazania pictured above that I grow in my yard..
Most gardeners realize that no garden or landscape remains static, that local and global ecologies change. In the end, I think most gardeners strive for balance among all their plants.
