Competitiveness of the Exotic Silphium perfoliatum against the Native Urtica dioica: A Field Experiment

Table 3

Effects on biomass of S. perfoliatum.

Parameter	Df	Estimate	F value
Treatment	2		182.91	<0.001
Year of growth	1	1.62	178.05	<0.001
Treatment × year of growth	2		3.47	0.040

LM calculated with living aboveground dry biomass (log-transformed) as the dependent variable. Independent variables were the treatment (control without competition, surrounded by S. perfoliatum, and surrounded by U. dioica), year of growth (1 to 2), and their interaction. Estimates are given for significant numerical parameters. They give the slope of the fitted regression line. Significant effects are highlitghed in bold type. LM: p < 0.001, Adjusted R² = 0.91, and n = 52.