Do male and female Lindera benzoin L. (Lauraceae) differ in stem mass/volume relationships and degree of lateral branching?1

Abstract

Males and females of the dioecious woody shrub Lindera benzoin (spicebush) have been shown to differ in stem volume (as estimated from basal area and stem heights taken from living plants). More specifically, prior to significant seed production, female plants may attain a larger prereproductive size. Thereafter, growth rates of males may be higher leading to larger average size as reproductive adults, presumably due to differential costs of reproduction. These previous studies have assumed that the sexes are similar in allometry, wood density, and degree of branching; therefore, stem volume could be used as a surrogate for aboveground biomass. This study addressed these assumptions using offspring derived from 15 maternal plants collected from a site in Maryland. Starting in 2013, plants were grown in pots to eliminate root competition and in a loose array to minimize shoot competition. By 2020, 229 of the plants that could be sexed (125 female and 104 male) were randomly selected for stem dry mass and branch number analysis. In agreement with previous studies, the largest stems of female plants had significantly higher volume than those of males. Stem mass/volume and basal area/height relationships did not, however, differ between males and females based upon regression models that did or did not contain sex as an independent variable. Therefore, stem mass was also higher for female plants. Males and females did not differ in the number of branches in the terminal meter of the stem or in stem density. These results suggest that prior studies utilizing stem volume as an indicator of stem mass were not likely biased by allometric differences between the sexes.