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 forest light environment (closed forest or large gap), branch type (branches from trees growing in closed forest or in the open) and branch spacing (15, 30, 45 cm) on light interception and transmission by Sugar Maple Acer saccharum. The artificial trees were created by cutting horizontal branches from mature trees and inserting the terminal Im of these branches into holes in a 160-cm high pole held vertically by a Christmas 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 were 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 divided by PPFD at the surface of the branch immediately above) showed a highly significant effect of branch type, branch spacing and an interaction between these two factors but no effect of forest light environment. Another factorial ANOVA of branch light interception (here defined 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 interaction between branch type and branch spacing. 3. This technique appears promising for the study of whole-tree architectural adaptations because branch architecture, tree architecture and light environment can be controlled and varied independently. Consequently, the functional significance of tree architectural parameters can be assessed independently and in any desired light environment.