The US has lost vast portions of its regionally distinctive flora and fauna to lawn-based yards. Lawns and traditional landscapes composed of relatively few ornamental plant species across the country have homogenized our nation. Landscape architects and installers across the country still use a limited palette of few species all over this country. As a result, these simplified landscapes resemble other climates and countries more then they do the US. As a result, yards in Maryland resemble yards in Utah, which resemble yards in northern Idaho.
Although many ornamentals commonly used in landscaping are not invasive, per say, the cumulative effect, as Tallamy and Shiropshire contend, is that they might as well be. Non-native ornamental species now cover the landscape as a result of commercial propagation and installation, so completely, and so effectively, that if you didn’t know the cause of the spread, you would think they are invasive species. What is the difference between purple loosestrife (Lythrum salicaria) or dalmatian toadflax (Linaria dalmatica) and arborvitae (Thuja occidentalis) , hosta (Hosta spp.) , or even petunias (Petunia spp.) when you add up the collective acreage?
Tallamy and Shiropshire demonstrate that native plants support significantly greater Lepidopteran species richness than common, non-native landscape plants that evolved elsewhere. Furthermore, they way butterflies used native plants was different and more diverse than the non-natives. For example, native plants attracted egg-laying females and supported their larvae, over an order of magnitude greater than with common non-native ornamental plants.
I commonly hear people justifying the use of commercially available, and regionally homogenous, cultivars by saying that they are ecologically similar to natives. As I have mentioned before, this is not the case. By definition, native insects have little or no evolutionary history with introduced plants, and thus the plants are of little use to them beyond occasional feeding, typically by adults (one short-lived life stage).
For example, it is common to hear gardeners extol the virtues of a non-native species that is a great plant for butterflies, because they see them feeding on it (Russian sage [Perovskia atriplicifolia], for example), and yet these plants are also touted for their insect and disease resistance. Planting individual, exotic species for individual wildlife species should be a thing of the past and we should think about native species and plant communities that provide for multiple animal families.
Homeowners should embrace the unique characteristics of their climate, geography and natural history when designing their garden. Native plant communities should be embraced and celebrated, rather than removed and converted to a landscape that could be found anywhere. As a group, homeowners can have a profound influence on the landscape. We need to recognize this and educate others about the positive beneficial effects or native plants as a basis for yards and demand more from nurseries, and public landscapes.