The Relative Water Demand of Five Urban Tree Species

Abstract

The relative water demand (RWD) of containergrown seedlings of red maple, green ash, Washington hawthorn, honeylocust and flowering crabapple was determined for the period mid-May through August by comparing water consumption values and potential evapotranspiration rates with growth rates. While RWD for red maple was high, actual water consumption based on changes in plant size (water use index, WUI) was quite low, indicating efficient use of available moisture. RWD for green ash was high, but WUI was also high indicating relative inefficiency in utilizing available water resources. RWD values for Washington hawthorn, honeylocust and flowering crabapple were all lowerthan those for maple or ash, while WUI values for these species were intermediate between maple and ash. In general, growth rate was not correlated with RWD. However, actual water consumption rates did correlate well with potential evapotranspiration as determined by the Thomthwaite equation.