Objective Betula albo-sinensis, a tall deciduous tree of the Betulaceae, unique to our country, is one of the main constructive species of warm temperate forests in China, with ornamental, economic as well as ecological values. Through the research on the structure and dynamic characteristics of red birch populations in two regions in the Qinling Mountains of northwestern China, clarifying the age structure characteristics and population dynamic changes, establishing the population development prediction model, and revealing the reason for the natural regeneration obstacle, we provided a theoretical basis for protection and restoration.
Method The two B. albo-sinensis populations in Huoditang Forest Farm (Ningshan County, Shaanxi Province) and Taoping Forest Farm (Li County, Gansu Province) were investigated and counted. Then the static life table was drawn, the population age structure and quantitative dynamic changes were analyzed, and a population development prediction model was established. Meanwhile, the development trend was revealed by the population dynamics quantification method and quantitative time series analysis method.
Result The age structure of the populations in the two regions was the most individuals at age Ⅲ, and the populations were mainly composed of young individuals. They both first declined and then increased in the early stage, then increased after a short decline in the middle term, and sharply dropped off at the age of Ⅵ−Ⅶ . The Taoping population was more susceptive to environmental factors, entered the decline period earlier than the Huoditang population. Their survival curves tended to be the Deevey-Ⅱ type.
Conclusion The age structure of the B. albo-sinensis populations in Huoditang and Taoping both presents irregular pyramids, and the population development is mainly maintained by middle-aged and elderly individuals. They are both growing populations at the current stage and highly dependent on habitat factors, especially obvious for Taoping. In the future, natural regeneration would be untoward for them because of lacking seedlings to various degrees. In response to these problems, several strategies to protect and restore: artificially cultivate seedlings and transplant them into the gaps of the populations; adopt the “5 times in 3 years” tending method for young forests, and the pruning, pruning, mowing, removing irrigation and the like for middle-aged forests. As for stands with a canopy density of more than 0.9, appropriate thinning is required to keep about 1 500 plants per hectare to improve the natural regeneration capacity of the populations.