Our hypothesis is that canopy location has an effect on the characteristic tensile strength of leaves, with the leaves on the top of the canopy having greater strength than the leaves on the bottom. We tested our experiment by sampling leaves from the top and bottom of three H. arbutifolia specimens, obtaining raw measurements of size, and testing the tensile strength of each leaf using the Instron. We performed t-tests on the data to determine if the average length, width, thickness, and tensile strength were statistically different depending on if our p values were < 0.05 when top and bottom leaves of the same tree were compared. We chose a chapparral stand removed from heavy human traffic and influence, eliminating as many extraneous variables as possible by taking leaves from the same tree of the same age from the same position on the branch and chose three trial specimen of similar height in the same area to reduce the possibility of varying sunlight exposure or water supply from affecting leaf morphology in a way that canopy position would not. The results show that blade length between top and bottom is statistically significantly different, while blade thickness and lateral strength at midsection were not statistically different. From our analysis of the data, it is clear that leaves on the bottom of the plant were longer and broader than leaves on the top, but we determined that canopy location does not have a major effect on tensile strength or thickness, supporting a null hypothesis.
Witham, Elena; Marchiano, Melinda; and Reynolds, Danielle, "Relationship Between Canopy Location and Tensile Strength of Leaves of Heteromeles arbutifolia in Malibu, CA" (2014). Pepperdine University, Featured Research. Paper 112.