Relationship of Transpiration, Reference Evapotranspiration and Tree Size During Six Years of Growth for Ilex x ‘Nellie R. Stevens'

Actual evapotranspiration (ET_A) of three Ilex x ‘Nellie R. Stevens’ trees  was determined continuously for six years using weighing lysimeters, as trees grew from rooted cuttings to 6 m in height.  Trees were grown in containers which are increased in diameter incrementally each year. Measured ET_A was composed principally of transpiration because tops of the containers were covered to limit evaporation.  Trees size, consisting of projected canopy area, tree height, and trunk circumference at 15 and 30 cm above substrate level and just below the first major branch collar, were recorded every three weeks.  Reference evapotranspiration (ETo) was calculated daily using an on-site weather station.  Measured  values of trees size were used to normalize ET_A.  Normalized ET_A values were then modeled as a function of ETo.  Justification for the best model and its implications will be discussed.