Abstract:

This paper studied the age structure and dynamic change of Nitraria tangutorun clonal ramet populations which naturally distribute at Jingtai, Gulang and Minqin in the southern margin area of Tengger Desert, as well as Lanzhou served as a control. The results showed as follows: The age structures of the four plots all belonged to progressive type. Along with the moisture gradient descending from south to north, the proportion of middle-aged ramets increased. There was a transition tendency from youth to adulthood. In the 4 plots, the static life tables all showed that youth ramet vitality and adaptability enhanced, life expectancy increased with age until Ⅴ age class, after which the life expectancy decreased gradually. The q_x and K_x obviously increased in Ⅲ and Ⅳ age class. The ramet population survival curves in the 4 plots all approached to Deevey type Ⅲ. The population bred exuberantly on the south hill in Lanzhou City, leading to severe space constraint and high infant mortality. The middle-aged ramets had low mortality at Baidunzi of Jingtai County and Malutan of Gulang County. Compared with other plots, the N. tangutorum clonal population at Qinfeng farm of Minqin County had higher mortality in all age classes, however, the ramet number in the age class Ⅵ increased unusually. The ramet survival analysis results were consistent in the 4 plots. The S(t) monotonically decreased and F(t) gradually increased with the age increasing. The F(t) and λ(t) of the populations on south hill in Lanzhou City were higher due to fierce competition, but were relatively lower at Qinfeng farm of Minqin County, probably as the population updated strategy to adapt harsh environment. The spectral analysis results showed that, the ramet age structure and dynamic change were mainly influenced by the biological characteristics in life cycle. The harmonic amplitude A₄ indicated the populations had to certain degree environment adaptability and anti-interference ability. Dynamic index V_pi″ showed that growth potential of the ramet populations gradually declined from south to north with the order of: South hill in Lanzhou City (1.27%)>Baidunzi of Jingtai County (0.37%)>Malutan of Gulang County (0.35%)>Qinfeng farm of Minqin County(0.24%). The population growth potential in the desert southern margin, especially Qinfeng farm of Minqin county, was limited. The N. tangutorum population should be protected by proper tending practices to enhance sustainable development.

Key words: Nitraria tangutorum clonal, population, ramet, age structure, dynamic index, static life table, survival analysis, spectral analysis, southern margin area of Tengger Desert