Relative competitive abilities and growth characteristics of a narrowly endemic and a geographically widespread Solidago species (Asteraceae)

Relative competitive ability and growth characteristics of the narrow endemic Solidago shortii were compared to those of the geographically widespread S. altissima. Competition and growth studies were conducted over the entire growing season in an ambient-temperature greenhouse, using a 3:1 (v/v) native limestone soil/river sand mixture. Results from a de Wit replacement series experiment (relative yield, relative yield total, plant height, aggressivity values) with S. shortii, S. altissima, and Festuca arundinacea (common competitor) suggested the following competitive hierarchy: S. altissima = F. arundinacea > S. shortii. Using classical growth analysis, we found that the competitive hierarchy was related closely to components of plant size (dry mass, height, leaf area, leaf area duration) and not to relative growth rate or any of its components (net assimilation rate, leaf area ratio, leaf weight ratio, specific leaf area). Solidago shortii allocated proportionately more dry mass to roots (but not to rhizomes) and had significantly greater root/shoot and (root + rhizome)/shoot ratios than did S. altissima. Thus, while the morphological traits of S. shortii enable it to tolerate drier habitats than S. altissima, in moist sites S. shortii easily would be overtopped and shaded out by S. altissima. Low competitive ability may be one of several factors contributing to the narrow endemism of S. shortii.