Leaf structural characteristics of 31 hardwood and conifer tree species in central Wisconsin: Influence of light regime and shade-tolerance rank

Leaf structural characteristics were examined in understory and open-growing individuals of 26 hardwood and five conifer tree species, representing a range of shade-tolerance classes, in central Wisconsin. Sun leaves of open-growing hardwoods generally had greater thickness, specific mass and stomatal density than shaded leaves in the understory. In contrast, the conifer species exhibited few consistent differences in sun-shade needle length and specific leaf mass. Guard-cell length was not consistently different between sun and shade leaves of the hardwood species. Oaks had greater leaf thickness and stomatal density but lower guard-cell lengths compared to other hardwoo. Shade-intolerant hardwood species generally had greater sun- and shade-leaf thickness, specific leaf mass and guard-cell length than more-tolerant species. These differences in hardwood leaves suggest that acclimation to light regime exists for species representing a broad range of tolerances, and that differences in sun-shade leaf structure among species may vary with shade tolerance.