Urban forests on the front line.
Charles Nock, Olivier Taugourdeau, Timothy Work, Christian Messier, Daniel Kneeshaw.
In their Review “The consequence of tree pests and diseases for ecosystem services” (15 November 2013, p. 823), I. L. Boyd et al. discuss the effects of pests on forest ecosystem services. However, urban forests garnered little attention.
With increasing global trade, urban trees are among the first affected by newly introduced pests. Low tree diversity combined with low tree density in cities limits the potential for compensatory responses of ecosystems, unlike the model presented by Boyd et al. Decades ago, diseased elms were felled en masse in cities in eastern North America; many of the same cities are bracing yet again for extensive canopy loss, this time due to emerald ash borer (1). Boyd et al. suggest that cultural services are affected, but a more complete portfolio includes services important to city dwellers, such as air pollution removal and climate regulation (2, 3).
As Boyd et al. suggest, planting more species and species selection will reduce losses to new tree pests. However, few species tolerate urban conditions, leading to overuse of those that do. Greater genetic diversity within species is particularly important to address enhanced pest risks in urban areas (4). Chemical treatments of urban trees can prolong their service life while also controlling pest spread (1). Outbreak-related tree removals cost millions. A greater investment in better infrastructure and soil [e.g., (5)] would be a cost-effective way to reduce stress and permit more species to be planted.