Gender Dimorphism in Growth and Mass Partitioning by Box-Elder (Acer negundo L.)

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Abstract
Sex ratio, growth rate, aboveground biomass allocation and phenology of the genders of Acer negundo were investigated. Male biased secondary sex ratios were consistent throughout 11 populations examined indicating that male bias is a real population phenomenon despite nonsignificance within most populations. Nonsignificant differences between genders in within-year growth (basal diameter) were found but significantly greater female growth occurred over the 1st 15 years of an individual''s life span. Regressions of harvest data showed males to have significantly more foliage mas (P <0.001), more inflorescences (P<0.001) and a greater mass in flowers (P<0.001). Females have greater total reproductive mass expenditure (P<0.001) and exceeded males in estimated seasonal wood production. Alghough male and female phenology differ significantly, it does not account for the observed differences in growth. Gender specific response to increased density is discussed using these and previously published results, suggesting that density is positively correlated with the degree of gender dimorphism. Our results contradict the idea that cost to a female''s growth and/or maintenance result from a relatively greater reproductive effort and indicate that greater consideration of demographic and ecological variables is required.