Gross branch production per species, year and organ type.

Mean±SE gross mass of stems (St), leaves (Lt), inflorescences (FLt) and infrutescences (FRt) produced per previous year stem in the invasive (Ailanthus altissima and Robinia pseudoacacia) and native (Populus alba) trees, in 2010 and in 2011. Different letters in the same variable and year indicate significant differences between species after a linear mixed model, with species and DBH as fix factors and individual as random factor, followed by a post-hoc Tukey test.