I was recently inspired by a new paper in Conservation Biology by Tallamy and Shropshire (download here), which demonstrates the importance of native plants over exotic plants in home gardens for Lepidopteran (butterfly) species diversity. This work compliments previous work by Tallamy I wrote about a few posts back. The authors bring up a lot of great points, and of particular interest to me is the notion that homeowners are a hugely influential group, locally and nationally, for conservation of plants and animals in this country. This should be empowering and validating for those interested in native plant gardening and wildlife gardening for conservation values. I think it is now necessary that homeonwers get on board with native plant and wildlife gardening if there is going to be meaningful conservation of biodiversity in North America.
Collectively, homes across the landscape create an ecosystem. Though it is a highly managed ecosystem, it has the tremendous potential for conservation of our regionally-unique flora and fauna. Unfortunately, in the past, managed-landscapes across this country have been influenced by colonial and imperialistic notions of what gardens should look like. These ideals were often derived from the English and the French aristocracy and applied uniformly across our diverse, and beautiful American landscape.
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.
In their paper, Tallamy and Shiropshire contend (based on conclusive data), that introduced ornamentals are very far from the ecological equivalents of native ornamentals. Butterflies are just one example, and a surrogate from many other species, and many higher trophic order species. Indeed, other researchers have found that there is a relationship between insect species richness and biomass, and bird species richness and diversity in urban or managed landscapes. Thus, the benefit of using native plants in landscaping transcends Lepidopterans, and continues through to birds. We need to reject the notion of "insect-free and homogenous" as being better than native plants. For years, landscapers and horticulturalists have selected for plants that are resistant to insect damage. And, as a result, many plants are labeled “pest free”. This may explain why Lepidopterans favor native plants. Remember, not all insects are pests, and in fact butterflies are insects!
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.
Tallamy and Shiropshire envision a tipping point is near- a time for a paradigm shift, and I hope so. The current landscape aesthetic of a lawn and exotic ornamentals is unsustainable and contrary to many goals common to all gardeners. The price of gas last year topped $4 a gallon and evidently that is what it took for Americans to change their driving habits. Bicycle sales skyrocketed, predictions of decreases in diabetes were extrapolated, and all this good that could come from change.
Now, so called “recession gardens” are here. Sales of vegetable seeds have increased to unprecedented levels, and many first–time vegetable gardeners are converting their lawns to something edible and useful. People are re-evaluating how they use their own yards and demand more of the same from our elected officials. Even the White House house has a new vegetable garden (even though from this picture, it appears Michelle Obama should read my post on how to remove a lawn. It pains me to see them using rakes to remove the lawn!)
Perhaps the tipping point is near and people will recognize that they are part of the landscape and the natural world, for better or worse. How homeowners manage their gardens influences the conservation of plants and animals on the landscape.