Abstract:

Objective: Four natural populations of Picea purpurea, Abies faxoniana, Pinus tabulaeformis and Quercus liaotungensis in Bailongjiang and Taohe forest regions in southern Gansu Province were investigated to characterize population structure, to reveal the current status of population survival and to predict future trend of population development, so as to provide a theoretical basis for the protection and sustain able management of the forests of the regions. Method: Based on field surveys and data analysis, population structure diagram were drawn, static life table were designed, survival curve were fitted and analysed. Quantification method was used to study the population dynamics, and population development trend were predicted by using time-sequence model. Result: There were sufficient seedlings of P. purpurea and A. faxoniana but with a high mortality, and the populations gradually become stable after the young age, survival curves of both populations conformed to Deevey-Ⅲ type, indicating expansion of the populations. P. tabulaeformis had also a larger percentage of seedlings, there was a peak of death in young age, middle age and middle old age, survival curve conformed to Deevey-Ⅱtype. The number of young individuals in the population of Q. liaotungensis was insufficient, with a peak of death occurred at young age and middle age, survival curve conformed to Deevey-Ⅱtype. The quantitative dynamic analysis also showed that the 4 populations are all growth type, and growth potential is ranked in the order of A. faxoniana > P. purpurea > P. tabulaeformis > Q. liaotungensis. The 4 populations all showed growth type when considering interference of external environment, and Q. liaotungensis has a high probability of disturbance, followed by P. tabuliformis, A. faxoniana and P. purpurea have a low probability of random interference by external factors. Time series prediction indicated that the number of individuals in the 4 populations will all increase after 2, 4, 6, 8 age classes in future, the proportion of population increase was positively correlated with the number of young individuals. Conclusion: The 4 populations were all growth type. P. purpurea and A. faxoniana were well naturally regenerated, with a stable population structure and great growth potential; the advantages of P. tabulaeformis seedlings was not obvious with small growth potential; Q. liaotungensis was poorly naturally regenerated, and it was vulnerable to external environment with the least growth potential. High mortality rate of young individuals was a "bottle neck" for natural regenerationand development of the population. Competition and self-thinning caused by the limitation of light and space what was the key factors leading to low survival rate of seedlings and saplings in seedling stage. Population regeneration of A. faxoniana and P. purpurea in a close-to-nature state have been affected mainly by their biological characteristics and environmental factors. P. tabulaeformis has been affected mainly by pests and diseases and Q. liaotungensis has been damaged mainly by human. For this reason, artificial measures should be taken to improve the survival rate of young individuals in A. faxoniana and P. purpurea and increasing the proportion of adult trees in the forest. It was necessary to strengthen pest control for P. tabulaeformis forest, and Q. Liaotungensis needs to strengthen protection and take artificial assistance to promote regeneration. Moreover, policy support was also needed to conserve forest resources in the region.

Key words: Southern Gansu, Bailongjiang, Taohe, natural forest, population structure