Healthy urban forestry practice comes down to one word – variety. Variety in plant species and horizontal layers provides a variety of niches for urban critters, especially birds. Variety keeps the forest healthy and can keep disease at bay. Urban parks with only a few tree species underlain with mown grass can quickly feel the effects of tree insect pests and diseases. For example, a monoculture of pine can be easily attacked by the Southern Pine Bark Beetle that recently devastated pine plantations in the Southeastern U.S. The best preventative treatment for pests and disease is growing a healthy, diverse forest that includes herbaceous plants, native grasses, fruit-bearing shrubs, and mixed-species trees.
Local-scale habitat features such as large canopy trees, berry-producing shrubs, and freshwater streams are of particular importance to attracting bird species. Landscape measures like forest canopy cover and park size significantly improve local-scale habitat features.(Urban Bird Diversity, Conservation Ecology)(Avian Diversity in Suburban Parks)
When the Birmingham Botanical Garden and an army of volunteers (Restoring the Olmstead Oaks) took over increasing plant diversity and forest health in George Ward Park, they improved the variety of trees both in age and species type. “Alabama is blessed with a lot of biodiversity because we missed the Ice Age,” said Trudy Evans of the Little Garden Club. “These trees are remnants of trees that were here that survived the Ice Age. So we are really preserving DNA. Most of these trees, like the post oaks, the black oaks, are not trees that you can find in nurseries.”
Birmingham-Southern College student Caroline Rowan studied the results of planting a variety of tree seedlings propagated from George Ward Park acorns. She found that 28 species of volunteer trees (a total of 750 individuals) came up in a three-acre area after urban forest management plans reduced mowing and leaf removal. She found 12 species (91 trees) of older trees and 13 species (316 trees) of planted trees in her study area. On the site, 84 herbaceous plants were found, with only two plots out of 75 lacking ground cover, therefore reducing erosion and increasing plant variety. More variety = more animal diversity, more bird species, and a healthier forest.