What the heck is an exotic plant anyway?
You hear assorted terms tossed around relating to the provenance of plants and animals, but what do they mean?
“Native” means the organism evolved in the area where it is residing. But of course, some areas are bigger than others. Giant sequoia trees and Tule elk are native to California, but not to Claremont. Even within smaller areas like Claremont, the local conditions dictate what is “native.”
Buckwheat, sagebrush and quail are native to the coastal sage scrub in the Bernard Field Station; mulefat and rushes were native to formerly wetter areas such as where Pilgrim Place is now. A native species can cover a very wide area or can be very restricted in its habitat—some insect species may only occupy a few acres. Saying a species is “endemic” means it is restricted to a particular area; bristlecone pines are endemic to high altitudes in the western US.
“Exotic” plants and animals are ones that haven’t evolved in an area. Hybrid tea roses, saguaro cactus, daffodils, corn, tomatoes, those pesky fox squirrels and our dogs and cats (and us) are all exotics in Claremont. The coast redwoods you see around town are native to California but exotic to Claremont.
Many exotic species do just fine when introduced to areas that have conditions similar to those in which they evolved or if the conditions they need are provided, and many don’t create any serious problems in their new location.
“Naturalized” species are exotic species that are well-adapted to a new habitat, which means that they treat the new area as their own and will grow and reproduce there without any outside help.
Sweet alyssum, black mustard, tree tobacco and Norway rats all will flourish locally without any help from us. In our urban gardens that get some degree of extra water, fertilizer or shade, many other exotic plants will seed themselves around.
In my garden, honesty, heavenly bamboo, violets, and fortnight lily appear in random spots but are easily removed where not wanted. Many species such as European honeybees were introduced intentionally and are so well-adapted to a variety of habitats that they have spread throughout the country.
“Invasive” species, however, are another kettle of fish (so to speak). Without the natural checks and balances that evolved with them, some exotic species naturalize so well that they start crowding out native species and altering the local ecology.
Argentine ants and zebra mussels came in accidentally, but Kudzu in the south and tamarisk in the desert were both introduced intentionally. Non-native annual grasses across California have changed the landscape, as has the fox squirrel that is spreading through the state is displacing our native gray squirrel. Fox squirrels are very adaptable and reproduce much faster than their gray cousins, so they are eating a lot more of our garden fruit and vegetables as well as new shoots on shrubs and trees.
Quite a few insect pests, such as the shothole borer currently attacking many trees in Claremont, are invasive exotics. Whether an exotic species is invasive or not varies—purple loosestrife, originally from Europe and Asia, can be a serious invader of wetland areas, but won’t be able to escape into the wild from gardens in dry areas like ours.
So, what does this mean for the ordinary Claremont citizen? Should you limit yourself only to local native plants and eschew all exotics?
If you want a garden entirely adapted to our local conditions, then maybe you do: we have some lovely plants that are native to the Claremont area such as buckwheat, toyon, penstemons and coast live oaks. But most of us gardeners find it hard to resist the amazing variety of plants that have evolved in other areas of the world, and want them all! So what to do?
My two cents: follow sustainable practices in your garden (you can find a helpful PDF on the garden club pages at sustainableclaremont.org); avoid any invasive plants in our area; include both natives and other plants that will support native insects and other wildlife; and most of all, don’t forget to have fun and make your garden a place you want to be!