RELATIONSHIPS BETWEEN STEM DIAMETER, SAPWOOD AREA, LEAF-AREA AND TRANSPIRATION IN A YOUNG MOUNTAIN ASH FOREST

We examined relationships between stem diameter, sapwood area, leaf ar ea and transpiration in a 15-year-old mountain ash (Eucalyptus regnans F. Muell.) forest containing silver wattle (Acacia dealbata Link.) as a suppressed overstory species and mountain hickory (Acacia frigescen s J.H, Willis) as an understory species. Stem diameter explained 93% o f the variation in leaf area, 96% of the variation in sapwood area and 88% of the variation in mean daily spring transpiration in 19 mountai n ash trees. In seven silver wattle trees, stem diameter explained 87% of the variation in sapwood area but was a poor predictor of the othe r variables. When transpiration measurements from individual trees wer e scaled up to a plot basis, using stem diameter values for 164 mounta in ash trees and 124 silver wattle trees, mean daily spring transpirat ion rates of the two species were 2.3 and 0.6 mm day(-1), respectively . The leaf area index of the plot was estimated directly by destructiv e sampling, and indirectly with an LAI-2000 plant canopy analyzer and by hemispherical canopy photography. All three methods gave similar re sults.