Effects of competition from introduced plants on establishment, survival, growth and reproduction of the rare plant Solidago shortii (Asteraceae)

Field and glasshouse studies investigated the effects of the introduced species Coronilla varia and Festuca arundinacea on establishment, survival, growth and reproduction of the federally-listed, endangered Solidago shortii (Asteraceae). All vegetation (mostly C. varia) in plots with S. shortii was removed in May 1993, and the plots were kept free of vegetation (except S. shortii) until September 1997 (treatment plots). Litter was removed from treatment plots each May 1993-1997. Neither vegetation nor litter was removed from control plots. Number of flowering and nonflowering ramets (stems) did not differ significantly between treatment and control plots in 1992 (year before vegetation removal). In treatment plots, number of flowering ramets of S. shortii increased significantly between 1992 and 1993 and then remained nearly constant from 1993 to 1996. In control plots, number of flowering ramets remained nearly constant from 1992 to 1996, and it was significantly lower than that in treatment plots from 1993 to 1996. Number of nonflowering ramets progressively increased in treatment plots from 1993 to 1996, while it remained nearly constant in control plots. Seedlings of S. shortii established only in treatment plots. Three percent of 1322 plants marked as seedlings in May 1994 were alive in September 1997, and about 0.4% of them had flowered by this date. At the end of four growing seasons, 36, 23, 18, 10 and 8% of the 39 surviving plants were in 3-10, 11-20, 21-30, 31-40 and 41-50 cm height classes, respectively; 5% of the plants were >50 cm tall. In a replacement series experiment, relative yield (RY) of S. shortii was significantly lower than the expected RY, whereas that of F. arundinacea was significantly higher than the expected RY. Relative yield total did not differ from one. The aggressivity value of S. shortii was significantly lower than that of F. arundinacea. Significantly fewer individuals of S. shortii flowered under inter- than under intraspecific competition. Thus, seedling establishment and vigor of S. shortii is highest in the absence of competitors, and future management practices will need to take this into account.