Water Use of Juvenile Live Oak (Quercus virginiana) Trees over Five Years in a Humid Climate

Trees planted in urban landscapes often require irrigation during all stages of life. Landscape tree water management requires reasonable estimates of water demand in order to schedule irrigation amounts and timing to conserve water while maintaining tree health. Estimating tree water demand is not straightforward for water demand of isolated trees as typically found in urban landscapes is affected by numerous factors.

To meet minimum spring flows, water management districts in Florida sought to make both agriculture and urban landscapes water efficient, which includes tree farms. Quercus virginiana, commonly known as live oak trees, is endemic to Central Florida and among the most popular landscape trees for their gracefulness and spreading shade.

In this study, to provide a basis for irrigation allocations both during production and in landscapes, daily actual evapotranspiration (ET_A) in liters for three live oak trees was measured with weighing lysimeters over five years, beginning with seedlings and continuing until trees averaged 7.2 meters in height. Empirical models were derived to calculate ET_A based on crown horizontal projected area (PCA) or trunk caliper (TCSA), adjusted daily by changes in evapotranspiration (ET_O). Average ET_A to produce these live oaks was 62,218 L cumulative over 5.5 years. Effectively transpiring leaf, tree water use volume divided by ET_O, was closely related to PCA over five years with the slope of this relationship being equivalent to a Plant Factor of 0.93. The product of ET_O and this Plant Factor can be used to estimate depth of live oak water demand in urban landscapes. Also, this Plant Factor can estimate water demand volume in nurseries and landscapes when combined with PCA, and similarly the slopes for TCSA can be used to estimate ET_A water volume from measured trunk diameter.

In conclusion, daily ET_A of Quercus virginiana can be estimated with high precision based on the methods of calculating ETO and using the appropriate coefficients (for PCA or TCSA) for a given measure of tree capacity to move and transpire water. 

Article by Richard C. Beeson, et al, from University of Florida, Apopka, FL, USA.

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Image by Ruy Urraca, from Flickr-cc.