Methods of assessing leaf-fracture properties

Numerous authors have attempted to quantify the physical properties of leav es in relation to aspects of leaf ecology, including decomposition, sclerop hylly, herbivory, and leaf function and longevity. This paper examines thr relative merits of the punch-and-die, tearing and shearing tt sts for asses sing leaf physical properties. We conducted a series of these three mechani cal tests on leaves of Solanum laciniatum, and determined the effect of var ious test parameters on the measurement of fracture properties. For the pun ch-and-die test, the parameters considered were machine speed, clearance be tween the punch and the die, edge definition of the punch, and area of the punch. Aspects of the tearing test examined were notch length, end effects, and length-to-width requirements of test strips, and for shearing tests th e effects of blade proximity, angle and sharpness were investigated. All th e lest parameters investigated were found significantly to affect the asses sment of leaf-fracture properties. In addition, fracture properties were fo und to vary significantly; within leaves. Some general principles for desig ning and implementing tests are outlined. This study suggests that while pu nching and shearing tests are useful means of quantifying leaf fracture pro perties, the value of the tearing test may be reduced as it is most constra ined bl: the biological nature of the test material.