Importance of a single population demographic census as a first step of threatened species conservation planning

Although analyses of species spatial distributions and genetic variation, creation of Red Lists and reserve design studies predominate in the plant conservation biology literature, in any conservation project they should be only a second step succeeding population demographic assessments. Demographic studies and analysis of the species regeneration niche are vital because only such studies can identify the factors that determine the population fate, the stages of the life-cycle that are most important for the population viability, and the regeneration niche parameters. Using published demographic data, we modelled a situation when either seed production or survival of emerging seedlings occur intermittently. We found that when recruitment occurs intermittently, the population size frequency distribution deviates from inverse J-curve, but no gaps in size classes are observed unless seed germination and/or survival of emerging seedlings are extremely rare events. Then we use these results to interprete population demography of ten threatened tree species from Wuling Mountains, China, and come to a conclusion that their demographic structure can not be a result of natural processes. Taken together, our results show how important even a single population census can be if it includes counting seedlings and saplings, for determining population viability and appropriate population management. Two types of populations must be recognized as requiring different managements strategies: with regeneration naturally occurring (even if limited) and with no seedlings/saplings present. Populations from the first category can be subjected to such management actions as reinforcement using plant material of appropriate origin. Planting conspecifics can boost regeneration through increased seed production. However, reinforcement will make no sense in populations in which lack of regeneration is due to reasons other than seed limitation. In such populations long-term monitoring and study program must be established to understand the reasons for lack of regeneration.