In talking with people about native plant landscaping, I often encounter folks who assume one or another drought-tolerant species must be a native plant. They’re surprised when I tell them that the plant comes from Australia or South Africa (for example). It’s a common mistake to equate drought-tolerant or “California friendly” plants with California natives*, but they’re not the same and can have very different impacts beyond the garden.
Kangaroo Paw is a drought-tolerant native -- of Australia.
I usually won’t include drought-tolerant non-natives in your design unless they’re already established in your landscape. I’ll say something like “I haven’t studied that species, so I don’t know how it fits in with the other natives I’d use in the design.” I select plants based on having compatible light, water, drainage, and flowering periods, as well as how they work together aesthetically, and I lack the same level of expertise with other species. But I could have devoted some attention to get to know these plants’ niches in the landscape, yet I haven’t. That’s because I fear that many so-called “California friendly” plants might turn out to be quite unfriendly to our natural environment in the long run.
To understand my thinking, you need to know that I’ve spent a couple decades doing botanical surveys in natural areas around southern California and I’m familiar with the devastating effects invasive species have on native plants and wildlife. Many species that are now choking out natural habitats were deliberately introduced for some reason – giant reed was planted for erosion control, eucalyptus were introduced for railroad ties – without considering their long-term effects.
Giant reed and tamarisk replace native willow forest.
These invasive species typically aren’t a problem for a few decades then the population just seems to take off, with higher densities where they’re already established and rapid spread into new areas. Suddenly, the species is everywhere and can only be controlled with massive, expensive effort (which doesn’t materialize on underfunded public lands). How does this happen?
When non-native plants are introduced into a new environment the insects and microbes that feed on them are not. This gives the novel species a competitive advantage over their native neighbors, which only grows with each new generation. Seedlings that spend less energy on defenses against their herbivores and parasites (who are no longer in the picture) can devote more energy to growth and seed production. Over several generations they lose more and more of these metabolically expensive defense mechanisms and use the energy to grow and spread faster. Then they escape the garden and we realize that we have a problem.
Pampas grass, popular in the garden, also thrives in meadows and near streams.
In southern California, the worst habitat degradation so far has been in riparian (stream side) areas, where water-loving ornamentals, such as Pampas grass and Mexican fan palm have displaced native trees, shrubs, and vines. Intact coastal sage scrub and chaparral have fared better so far (except when non-native grasses invade after fire), but a look at any local canyon and will show invasive species eating away at the habitat from the edges.
I fear that with widespread planting of drought-tolerant ornamentals we will repeat the same devastating process in upland habitats that has already occurred along our streams and rivers. So, I avoid “California friendly” plants because I don’t want future nature lovers to curse me with the same vehemence that I’ve used on the benighted people responsible for the invasive species that currently plague us.
Mexican Sage -- in the garden today, in the canyons tomorrow?
*Note: Be Water Wise’s Top Ten California Friendly plants are all native; The Garden’s list contains both native and non-natives.