PHYSICAL SIMULATION OF TREES TO STUDY THE EFFECTS OF FOREST LIGHT ENVIRONMENT, BRANCH TYPE AND BRANCH SPACING ON LIGHT INTERCEPTION AND TRANSMISSION

1. Artificially constructed trees were used to study the effects of fo rest light environment (closed forest or large gap), branch type (bran ches from trees growing in closed forest or in the open) and branch sp acing (15, 30, 45 cm) on light interception and transmission by Sugar Maple Acer saccharum. The artificial trees were created by cutting hor izontal branches from mature trees and inserting the terminal Im of th ese branches into holes in a 160-cm high pole held vertically by a Chr istmas tree base. Three Vertical rows of three branches, separated by 120 degrees, constituted the tree. The articial tree made it possible to vary the horizontal spacing of branches as well as move the tree to any desired environment (here, a large canopy gap and closed forest). Light transmission through the crown and interception by branches wer e measured at several points within the reconstructed crown with a LI- COR quantum sensor under overcast conditions. 2. A factorial ANOVA Of light transmission (here defined as PPFD at the surface of a branch di vided by PPFD at the surface of the branch immediately above) showed a highly significant effect of branch type, branch spacing and an inter action between these two factors but no effect of forest light environ ment. Another factorial ANOVA of branch light interception (here defin ed as PPFD 10cm below a branch divided by PPFD measured at the branch' s upper surface) showed a significant effect of branch type and an int eraction between branch type and branch spacing. 3. This technique app ears promising for the study of whole-tree architectural adaptations b ecause branch architecture, tree architecture and light environment ca n be controlled and varied independently. Consequently, the functional significance of tree architectural parameters can be assessed indepen dently and in any desired light environment.