The Regeneration And Natural Development Of Plantations Of The Hippophae Rhamnoides Population Standing In Hilly Loess Regions

In this paper, the artificial Hippophae rhamnoides population are taken as the research object in the gullied loess plateaus. Through the investigation of typical sample plots and laboratory experiment, this paper conducts a systematic study about the biological-ecological characteristics, community structure characteristics, population characteristics of sexual reproduction and asexual reproduction, dry matter allocation, as well as the evaluation method for the plantation communities naturalized development, identifies the optimum growth of regional of artificial Hippophae rhamnoides population in the gullied loess plateaus, and provides basis for the natural cultivation of the artificial Hippophae rhamnoides population. The main results are as follows:(1) In the gullied loess plateaus, the flowering, fruiting and seeds scattering of artificial Hippophae rhamnoides population are normal, and the seed yield is relatively high. But after the seeds fall, there are little to settle. The sexual reproduction is difficult to maintain the population regeneration in this region. Light has a positive impact on Hippophae rhamnoides, but water and temperature bad is a key factor which limits the seed germination growing into seedling.(2) The natural regeneration of artificial Hippophae rhamnoides population mainly depend on root sucker and root sprout after stumping, they are both produced by the asexual propagation of stock plant. Root sucker plays a more important role in the expansion of population, mainly in guerilla distribution; after stumping, root sprout initiates from 5cm high stump. Asexual propagation of Hippophae rhamnoides in gully bottom is more vigorous than that in others, just as gully bottom>shade slope>replat top>sunny slope. The major environmental factors affect the asexual propagation of Hippophae rhamnoides are water and light.Statistic the age structure of clonal ramets and the result shows: Artificial Hippophae rhamnoides population in different habitats all present the phenomenon of more young individuals and less older individuals. The phenomenon indicates artificial Hippophae rhamnoides population have the strong expansion capacity. The death and whither of population have little impact on artificial Hippophae rhamnoides population, because there are enough ramets to maintain the population regeneration, and they can achieve natural development.(3) Species diversity changes with the change of external environment in the period of development. The water is key factor. In the gullied loess plateaus, Hippophae rhamnoides population which is good and vigorous, have function of conservation of soil and water. So they can achieve natural development.(4) The comparison results of total clonal dry weight in different habitats as follows: gully bottom>shade slope>replat top>sunny slope; the root-shoot ratio of standard plants are: gully bottom (1:1.56)<shade slope (1:1.08)<replat top (1:0.72) <sunny slope (1:0.61). These show that artificial Hippophae rhamnoides population in the gullied loess plateaus through the way of reducing the dry weight on the ground and expanding the underground root system to adapt to arid environment with water reducing.(5) In the paper, using structure of age, structure of community, diversity of species, thickness of dead branches deciduous layer, soil crust, nutrient and moisture of soil, and so on. Based on fuzzy membership function synthetic evaluation model, the plantation community naturalized development was evaluated. The result shows that gully bottom>shade slope>replat top>sunny slope.