Response of population structure and dynamics of Hippophae tibetana, a pioneer species of succession to altitudinal gradients in the Qilian Mountains
Zongqi Ma Pengfei Gao Baoli Fan Kun SUN
Chin J Plant Ecol. 2022, 46 (5):
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Aims The characteristics of population structure and the quantitative dynamics of plants can reflect their living status and reveal the relationship between population and environment. H. tibetana was a dwarf shrub, and a pioneer species of vegetation succession which was peculiar to the alpine region of Qingzang Plateau, with excellent water and soil conservation effects and good ecological adaptability to high-altitude environment. However, there were few research on the response of population structure and dynamics to altitude gradient, which were not conducive to understanding the ecological strategy of H. tibetana adaptation to alpine habitats. The Qilian Mountains in the northeastern margin of the Qingzang Plateau were ecologically fragile, and H. tibetana as a native species were often patchy distributed in alpine degraded grassland at an altitude of about 2 700–3 300 m, which played an important role in the maintenance of water conservation forest in this region.
Methods The structure characteristics, survival status and morphological characteristics of H. tibetana populations distributed at three altitudes (2 868 m, 3 012 m, and 3 244 m) in Tianzhu County, Qilian Mountains were described by establishing static life tables and drawing population survival curves. The population dynamic quantitative analysis and time-sequence model were quantitatively used to determine its future development trend.
Important findings The results showed as follows: 1) The plant height, basal diameter and crown width of H. tibetana decreased with elevation; The age structures of all populations at the three altitudes were roughly spindle-shaped, with abundant mature individuals but a few seedlings and old ones, and the mature ones could maintain population stable currently. 2) The survival curves of all populations tended to approach the Deevey-II type, and the survival ability were largest in low altitude, medium in middle altitude, and lowest in high-altitude. The mortality and disappearance rates were both high with the same trends, which were ranking from highest to lowest were high-altitude > low-altitude > middle-altitude, and all of them were abundant of seedlings, indicating that all of them would decline, and a decline was likely to occur in high altitude earliest and quickest. The life expectancy of old individuals were middle-altitude > low-altitude > high-altitude. 3) The dynamic index (Vpi') of each altitude population was close to 0, indicating that all populations were stable, and the maximum of probability under random disturbance (Pmax) of the middle altitude population was the smallest, which showed that the middle-altitude populations were the most stable to random interference. And the middle altitude was the most suitable for the growth of H. tibetana. 4) The proportion of seedlings of the all populations will decrease, while the mature and old ones will increase after the next 2, 4 and 6 age classes of time. The all populations at three altitudes will decline, and the lack of young individuals, interspecific and intraspecific competition, and environmental stress could be the major causes for population declines of the all populations. Based on the above results, it will help to scientifically predict the growth and death of H. tibetana populations in the future, provide reliable theoretical foundation for the protection of natural forests in this region, and reliable data support for the prediction of altitudinal distribution of alpine plants under the global climate.