HYDRAULIC ARCHITECTURE OF ACER-SACCHARUM AND A-RUBRUM - COMPARISON OF BRANCHES TO WHOLE TREES AND THE CONTRIBUTION OF LEAVES TO HYDRAULIC RESISTANCE

Hydraulic resistance to water flow was measured in the xylem and leaves of above-ground portions of Acer saccharum and Acer rubrum for trees with trunk diameters (D) ranging from 0.02 to 0.2 m. Resistance (area basis) to water flow in leaves and petioles was 24 and 13 x 10(3) MPa m(2) s kg(-1) for A. saccharum and A. rubrum, respectively. Leaf area of whole trees was proportional to D-1.82. Absolute xylem resistance (MPa s kg(-1) was proportional to D--1.64. SO xylem resistance (area basis) was proportional to D-0.2, which was not significantly different from a zero dependence (DO) for D less than or equal to 0.2 m. On a leaf area basis, the resistance to water flow in the whole shoots was found to be approximately 50% in leaves and petioles, 35% in crown xylem, and 15% in trunk xylem for D less than or equal to 0.2 m.