A 3-year study of water relations of urban street trees.
Results are presented from a study of 20 street trees (8 on the E. side of the street, 12 on the W. side, 9 Fraxinus pennsylvanica, 11 Tilia cordata) in Manhattan, New York City in July-September 1983, May-September 1984 and June-August 1985. Water deficit (midday stomatal closure) occurred less frequently than expected, and was demand driven rather than supply limited. Deficit occurred with air temperatures >41°C and maximum atmospheric vapour pressure deficit 7.5 kPa. Microclimate in the street was much drier and hotter than in a nearby park. Trees on the W. side (receiving more solar radiation) were not more stressed than those on the E. side. Differences between species in transpiration rates and responses to irrigation were not significant.