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

Table 6

Relative neighbor effect (RNE) based on growth and reproductive parameters.

Central species	Year of growth	n	Surrounding species	Plant height	Projection area	Number of shoots per plant	Number of capitula per plant
S. perfoliatum	2	9	S. perfoliatum	0.01	0.82	0.68	0.92
		8	U. dioica	0.11	0.71	0.81	0.89
	3	9	S. perfoliatum	0.04	0.58	0.77	0.94
		8	U. dioica	0.14	0.52	0.86	0.89
	4	9	S. perfoliatum	0.21	0.89	0.83	1.00
		8	U. dioica	0.16	0.83	0.88	0.82
	2–4	27	S. perfoliatum	0.07	0.70	0.77	0.94
		24	U. dioica	0.14	0.62	0.86	0.88
U. dioica	2	9	S. perfoliatum	−0.02	−0.06	No data
		9	U. dioica	0.09	0.89
	3	9	S. perfoliatum	0.26	0.53
		9	U. dioica	0.03	0.81
	4	9	S. perfoliatum	0.00	0.82
		9	U. dioica	0.05	0.93
	2–4	27	S. perfoliatum	0.10	0.43
		27	U. dioica	0.06	0.85

RNE is calculated as equation (1). The higher the RNE is, the higher is the competitive effect. Bold type indicates that the parameter in the given treatment is significantly lower than the control. indicates that the parameter in the given treatment is significantly lower than in the treatment with the other surrounding species. Tukey’s post hoc tests on LMs with nontransformed plant height or log-transformed projection area and on GLMs with Poisson-distribution with the number of shoots or number of capitula per plant.