PREDICTING POTENTIAL TRANSPIRATION OF SINGLELEAF PINYON - AN ADAPTATION OF THE POTOMETER METHOD

Estimates of singleleaf pinyon (Pinus monophylla Tort. and Frem.) potential water use were conducted on the Virginia Range, Nevada, based on crown dimensions and needle biomass. A modified potometer method was developed to measure whole-tree transpiration over an 8 h period. Water uptake from the potometer was positively related to both the foliar mass plus the average number of resin canals in the needles of each tree. Water uptake was also positively related to the total crown needle surface area (cm2) plus the average resin canal number. Best predictive equations based on standard error of the estimate analyses were obtained with nonlinear regression analysis of untransformed data. Pinyon populations with higher resin canal numbers are generally found in locations with higher temperatures and drier summer conditions.