I have finally, after years of hearing about it, read Douglas Tallamy's 2007 book Bringing Nature Home. I have felt that I have been doing my part to help the environment in my public and private gardens. I have planted native as well as exotic plants in my gardens but have been careful to remove invasive plants like barberry, burning bush and bittersweet from the gardens. I have tried to plant trees and shrubs to provide food and shelter for birds. What I didn't understand was the importance of the foliage of native plants, in particular woody plants, as a source of food for insects which, in turn, supply food for birds, reptiles, amphibians and small mammals.
Tallamy has shown that most insects will only eat the foliage of trees and shrubs (with the exception of crabapples and several other exotic species) which they have evolved with for thousands of years. So my beautiful Katsura tree, Cercidiphyllum japonicum or the trifolaite maples, Acer triflorum and A. griseum x 'Gingerbread', that I adore, are not contributing to the food chain and biodiversity which is so important to our ecology. The good news is that oak trees are the number one woody plant to support Lepidoptera (bird food) and "serve as a host plant for 534 species of moths and butterfles." The two red oaks in my garden are making a huge contribution to biodiversity.
Tallamy maintains that "woody plants support much more biodiversity than herbaceous perennials and annuals. So, being creative with alien herbaceous plants is less harmful than using woody aliens. The number one herbaceous genus is Solidago, the goldenrods, but they only support 115 species. That is still a lot of biodiversity, but it is nearly five times less than oaks".
So it turns out, I haven't been doing as badly as I thought. All the public gardens have numerous crabapples which provide 311 species of Lepidoptera. The river birches, Betula nigra 'Heritage' that Gordon Hayward recommended at Depot Park support 413 species. The sugar maples at Teixeira Park provide 285 species and the beech trees at Putnam Park support 126 species.
My New Year's Resolution is to continue to pay attention to native plants in my public and private gardens. I love to experiment with exotic plants, but if I pay particular attention to the woody plants and make sure I have plenty of native asters, goldenrods, milkweeds and Joe Pye weeds, maybe I can have the best of both worlds.