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a, Model including a plot random effect. b, Model including the effect of stem density. Both models are for trees ≥ 10 mm dbh. Stem density was calculated as the number of stems ≥ 100 mm diameter. P values were not calculated, but t-values < −2 or >2 are generally significant at P > 0.05 for sample sizes >60. Response variable = log(growth); number of observations = 18,970; number of species = 541.