Native red maple tree infested with scale insects. Notice dead twigs, leaf loss, and thinning canopy due to scale insect feeding and environmental stress. Photo: SD Frank

Many scientists, conservationists, and gardeners advocate planting native trees as a way to enhance conservation in urban areas. This is based on the assertion that native trees support more caterpillars and other insects than exotic trees and thus more birds. Native trees often do support more herbivores but, unfortunately, this means they could also have more pests. Exotic trees may be less susceptible to herbivores but provide less conservation value as a consequence.
Conflicts between conservation and pest management goals are not often addressed by native plant advocates. Red maples and willow oaks, both native and common urban trees, frequently become so infested with scale insects that insecticides are applied to preserve tree health and beauty. A native tree sprayed with insecticide is probably of little conservation value.
A red maple branch heavily infested with gloomy scales. Photo: AG Dale

Also, birds are not the only beneficiaries of tree services. People need trees to cool urban environments, filter air, and make urban spaces generally more healthful and pleasant. However, pest infestations are often worst on trees in the most urban areas where people need trees the most. Exotic trees, with fewer pests, may flourish in these sites to benefit people even if not birds.