Transpiration From 100-yr-old Lodgepole Pine Forests Estimated with Whole-Tree Potometers

Abstract

Whole-tree potometers were used to estimate transpiration from two contrasting stands of 100-yr-old lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) forest growing on the same site in southeastern Wyoming. Although one stand had nearly seven times as many trees per hectare and 29% less biomass, both stands had nearly identical leaf area indices (7.3 and 7.1) and clear-day transpiration rates (3.3 and 3.4 mm/d). Individual tree basal area and maximum observed 24-h uptake were highly correlated, with the largest trees (20-26 cm dbh) transpiring 40-44 L on clear days in early summer. Maximum observed hourly uptake for the larger trees was 2.5-3.5 L, with total nighttime uptake being about 12% of 24-h uptake. On overcast days potometer uptake was reduced by 30-44%; during rainy periods uptake was reduced to nearly zero. The results are compared to data obtained with different methods by other investigators, with the conclusion that whole-tree potometers can be a useful tool for studies on tree water relations and for estimating short-term forest transpiration when leaf water potential is not limiting leaf conductance.