Heteromeles arbutifolia an important chaparral species of southern California, Is a food source for mule deer (Odocoileus hemionus). This predation has become more pronounced as the climate shifts to hotter, drier, and longer summers. Other species that the deer normally feed on cannot survive these harsh conditions, while Heteromeles arbutifolia is able to persevere (Letourneau, 2004). We decided that there must be mechanisms involved in the petiole of leafs to keep them from being pulled off by deer and strong winds. Our group hypothesized that as the angle between the petiole and branchlet increased, the tensile strength of the petiole would decrease. Testing was completed on an Instron tension tester to gather data about the petiole’s strength. The subject of this experimentation was adult Heteromeles arbutifolia (Toyon) from the Pepperdine campus in Malibu, California. By measuring both natural and anthropogenic angles we were unable to see any correlation between the angle and Modulus of strength. In future studies perhaps more samples would be able to tease out a trend unseen in the data points collected by our group. The petiole’s resistance to pulling may also be more dependent on other evolutionary factors, such as petiole diameter and fibrous content.
Andrus, Matt W.; Lisankis, Anthony P.; and Anderson, Valen C., "Effect of Petiole-to-Branchlet Angle on Tensile Stress and Tensile Strength in Heteromeles arbutifolia" (2010). Pepperdine University, All Undergraduate Student Research. Paper 24.