Environmental requirements of three threatened plants on limestone glades in Southern Missouri

Information on critical area required to ensure the long-term survival of plant populations is lacking for the development of conservation policy. Here we examine the relative importance of critical area and environmental factors to the distribution of a threatened perennial Penstemon cobaea, biennial Stenosiphon linifolius, and annual Centarium texense on limestone glades in southern Missouri. Two of three plants show a glade-size dependent distribution: P. cobaea colonised large and S. linifolius small glades. C. texense successfully colonised glades of all sizes. Environmental requirements of populations of the three species differed, but overlap in range was evident. Diffuse competition may account for the observed patterns in distribution but further study is required. In the interim, we suggest that a useful approach for developing a conservation policy for natural plant communities is the intensive study of a few plant species with contrasting life-history strategies.