A summary of some key concepts in talks given or prepared by Thomas Wessels and Douglas Tallamy at the “New Directions in the American Landscape” symposium at Connecticut College in New London in January of 2007, with added thoughts that their presentations inspired.
Our native plants and animals evolved together over long periods of time, achieving a balance of benefit to all the organisms. When two kinds of organisms first meet, the interaction may be disastrous—as for example, gypsy moths meeting North American trees. Over time—often many thousands of years - their interaction usually evolves so that they co-exist in a balance of benefit to both species.
Non-native plants did not evolve in our ecosystems. Non-native plants do not provide the food needed by our native animals. The first step in the food chain are herbivores, those animals that eat plants. The primary herbivores in our native web are insects. Ninety percent of herbivorous insects are specialists that feed on only one or a few species of plants, plants that have the specific chemicals that co-evolved with the insects. If these plants aren't present, the insects won't have the appropriate food, which means that the organisms which would have eaten the insects, and the organisms which would have eaten the organisms that ate the insects, etc, etc may not have their usual food supply.
When you see a few chewed leaves on a plant, don't automatically think: “Yikes, how do I get rid of this pest”, instead think: it as “Wow, this plant is feeding something”. If the damage is severe, the plant may be feeding an alien organism that didn't evolve in that ecosystem, as when oak trees are feeding gypsy moths. A healthy community of native plants, although providing food for many insects, is not defoliated.
Non-native plants such as Norway maple may look neat and pristine precisely because they are not contributing to the food chain. Monoculture stands of Norway maple in our country have been reported to be eerily quiet—no chewing insects, no birds. Native plants support 29 times as many kinds of caterpillars as non-native plants. Cornus florida, our native flowering dogwood, supports 118 kinds of native caterpillars. The oriental flowering dogwood, Cornus kousa, supports one. Oak trees feed over 500 kinds of moth and butterfly larvae. Our native Joe Pye weeds support 41 kinds. Black cherry (admittedly an annoying garden plant) supports 455 kinds. No North American butterflies can reproduce on Buddleia (Butterfly Bush).
Nearly all baby birds—96%— eat insects. In preliminary studies, landscapes with predominantly native flora supported more, sometimes as much as two times as many—breeding birds as traditionally landscaped properties.
Complex ecosystems—i.e. those with the greatest amount of biodiversity—are more stable, more productive, and less susceptible to invasion. At first glance, adding plants from other parts of the world might appear to increase biodiversity. But it does not. Adding a non-native plant brings only that plant, while each native plant brings with it an large array of insects and other animals that are ulitmately dependent on the plant for food.
Ninety five percent (95%!) of the lower forty-eight United States is either cities/suburbs (54%) or agricultural land (41%). The untouched 5% is often fragmented into parcels which are too small to be able to maintain their original biodiversity. Our non-native lawns and plantings are not part of a balanced web. They do not encourage a diversity of animal species. They fail to contribute complexity to our formerly productive and balanced ecosystems. To increase biodiversity, we need to increase biodiversity in our suburbs and in our gardens. We can do that by planting the native flora on which the native fauna depends.
Entering the nursery area, June.
The lovely yellow daisy, Ratibida pinnata with the blue spikes of Agastache anisata, set off by the neat variegated foliage of Daphne 'Carol Mackie'.
The delicate cloud of white flowers of Calmintha nepeta nepeta surrounded by the bright pink flowers of a sedum and the dark purple foliage of annual Perilla and non-hardy Pennisetum setaceum 'Rubrum'.
The enormous yellow-green leaves of Hosta 'Sum and Substance' with the gold-variegated foliage of the soft grass, Hakonechloa macra 'Aureola'.
The incredibly bright flowers of a Vernonia blooming in late summer or early fall. My favorite is the Connecticut native Vernonia novaboracensis, which flowers for me in September, on six foot stems.
Have you hugged a plant today? Amsonia hubrichtii, a big bushy and beautifully soft plant in early September.
Amsonia hubrichtii in late September, as it starts to turn buttery yellow.
Northern Sea Oats, Chasmanthium latifolium , is a native grass for partly shaded to sunny-but-not-baked sites. The foliage is a cheerful bright yellow-green until fall, when both the foliage and the lovely dangling-oatmeal sprays of seeds turn a beautiful rusty-apricot color. The strong wiry stems will stand all winter in the snow.