Janet A. Morrison. The New York Botanical Garden, Bronx NY. Dogwood decline and disease along urban-rural gradients.
Metropolitan areas present problematic environmental conditions for natural plant populations remaining in parks and woodlots, but which evolved in more pristine conditions. Plant resistance to disease is one important facet of plant ecology that may be affected. Flowering dogwood is subject to dogwood anthracnose, caused by the fungus Discula destructiva. As an initial test of whether trees in forested areas within urban centers exhibit greater decline and more disease, in the New York City region I sampled 18 trees each from three urban, three suburban, and three rural forests with similar dogwood densities. Urban forest trees had significantly more epicormic sprouting and somewhat more lower branch die-back ; both are anthracnose symptoms and/or response to other stressors. Urban trees also had larger DBH, indicting possibly greater age, which could influence disease susceptibility and decline. However, there was no relationship between DBH and either symptom. Compared to the urban and suburban forests, rural forest trees were significantly less likely to have Discula present and sporulating on leaves, and there was no relationship between presence of fungus and DBH. These results present some evidence that tree decline is more pronounced at the urban end or urban-rural gradients, and that it might be due to increased effects of pant pathogens in metropolitan environments.