Spatial distribution of declining urban maples

Patterns of distribution and change for Norway, sugar, and silver maple trees with scorch, chlorosis, small dead limb, and large dead limb symptoms were analyzed with statistical techniques, using data collected between 1975 and 1977 in Syracuse, NY. Increases in symptom severity and numbers of trees affected indicate a general increase in maple decline of the population over the 3-year-period. Nearest neighbor analysis procedure showed that symptomatic trees occur in non-random spatial patterns. Trees with scorch and dead branch symptoms were distributed in a linear pattern while trees with chlorosis were grouped in a concentrated circular pattern. There was little evidence for spread of decline from symptomatic to healthy trees. No change in the degree of aggregation of symptomatic trees was observed over the three years of observation. Scorch of Norway maple leaves was the only symptom that could be associated with an agent that spreads from tree to tree but the overall level of scorch in the population remained relatively constant.