Reasonable Guidelines for Street Tree Diversity

Street tree diversity should relate to acommunity's range of conditions and objectives for the trees, and therefore is best increased by improved planting sites that can support more species. It is illogical to try to increase street tree diversity by simple numerical limits on replanting common, provenadapted species if this encourages more use of unproven or less-adapted species. Alternative guidelines are suggested for evaluating local populations, determining whether common species are overused, and testing additional species. Diversity also must relate to scale. While few species may be appropriate for a particular local situation, wide promotion of species through national markets is questioned. Also, wide promotion of a few cultivars within common species is criticized in the interests of reasonable biodiversity.