Cespitose Population Structure and Dynamics of Rare Fraxinus sogdiana in the Yili River Valley, China

Fraxinus sogdiana Bunge is a class II key protected plant in China, known as the “living fossil of broad-leaved trees”. It is commonly found in multi-stemmed cespitose forms created by the sprouting of its root systems and stumps. We sampled plots in the east and west of the Kashi River in the Xinjiang Yili F. sogdiana National Nature Reserve. We investigated the cespitose F. sogdiana by using population ecology methods in order to provide scientific information for the conservation and sustainable development of the species as well as for the management of the reserve. We chose diameter class structure instead of age class structure to establish a population static life table, draw population survival and mortality curves, calculate a population dynamic index, and use spectral analysis to explore the fluctuation cycle of the population. The results show that age classes II–IV, comprising 74.72%, 91.53%, and 81.77% of the two cespitose populations in the east and west of the Kashi River and the total population, respectively, showed that the populations had a growing age structure. Still, there were very few individuals in age class I. The survival curves tended to be the Deevey–II type, with peak mortality occurring at age class IX in the east of the Kashi River and age class V in the west of the Kashi River. The dynamic index of populations changed the Vpi in the east and west of the Kashi River and the total population were greater than 0, indicating they were growing-type populations, and the V′pi of the east of the Kashi River population was closer to 0, meaning that this population was relatively more resilient to external disturbances. Spectral analysis revealed that the periodic fluctuation of the population was mainly controlled by the biological characteristics of the population. Additionally, the east of the Kashi River population and the total population exhibited obvious multi-harmonic small periodic fluctuations. We suggest that the habitat of the cespitose F. sogdiana populations should be protected and improved to strengthen the nurturing management of individuals of age classes I and II for maintaining the natural renewal and development of the population.