Trees for urban planting: diversity uniformity, and common sense
AbstractA broader diversity of trees is needed in our urban landscapes to guard against the possibility
of large-scale devastation by both native and introduced insect and disease pests. Urban
foresters and municipal arborists should use the following guidelines for tree diversity within
their areas of jurisdiction: (1) plant no more than 10% of any species, (2) no more than 20 %
of any genus, and (3) no more than 30 % of any family. Strips or blocks of uniformity (species,
cultivars, or clones of proven adaptability) should be scattered throughout the city to achieve
spatial as well as biological diversity. Terms such as “monoculture”, "cultivar" , and “clone” are
discussed and a rationale is provided for the planting recommendations. The potential problems
of graft incompatibility in some species are considered in the light of recent research.
Alternate TitleConference of the Metropolitan Tree Planting Alliance (METRA).