3.2. Intensity of interspecific competition
Both the type of competitors (old vs. new; CompType) and the nitrogen
treatments (NTC) had significant effects on the relative competition
index (RCI), and the interactions between PopType and NTC were
significant (Table 2). In general, the competition was stronger (i.e.,
higher values of RCI) when G. quadriradiata was planted with old
competitors then planted with the new competitors (Fig. 3), and the RCI
value increased with the nitrogen addition (Fig. 3). When under ambient
nitrogen, the interspecific competition was significantly stronger for
the edge population when compared to the central population (Fig. S2).
There was no statistically significant difference in the interspecific
competition between edge and central populations when under low and high
nitrogen treatments (Fig. S2).