Research Of Plant Community Successional Series In The Malan Forest Area On The Loess Plateau

It is imperative under the situation to accelerate the recovery and restoration of degenerative ecosystem on loess plateau because the ecosystem is seriously degraded due to soil and groundwater depletion. Malan forest area, in the south of Ziwulin area, is a relative intact natural secondary forest on loess plateau and is important for loess plateau central area. Ziwulin area has crucial effect for maintaining regional climate and as a base for ecologically sustainable economic development in east Gansu and north Shaanxi provinces. So, the research of plant community successional series has significant ecologic meaning for recovery and restoration of degenerative ecosystem.In this dissertation, the studies of plant community successional series in Malan forest area, niche characteristics of common plant species, characters of gaps, disturbance status and gap regeneration of Quercus liaotungensis and Pinus tabulaeformis are carried on and got the results as follow:1. Malan forest area was composed with various plant community successional stages. The plant community successional series were divided into nine stages in this area with a trend over time from herb- to shrub- to tree-dominated communities with DCA analysis. The climatic climax was a Q. liaotungensis community. Artificial P. tabulaeformis community was a relative stable community under human disturbance. Over time, the number of families, genera and species increased. The species richness of every life form group increased and the compositional proportion became more consistent over time. Litter and humus thickness increased over successional time, however, the ratio of litter to humus differed among successional stages.2. In the forest successional series, the niche breadths of common tree species were smaller than that of common shrub species, and some companion species had larger niche breadths than dominant species. Species with large niche breadths tended to overlap with other species highly and vice versa, even those with smaller niche breadths sometimes had no overlap at all. Because of the distinction of species bio-ecological characteristics and environmental heterogeneity, some species with large niche breadths had low niche overlaps with each other and some narrow niche specieshad high niche overlaps with each other. High niche overlaps also occurred between species in the same genera.3. Medium and little gaps were majority in Malan forest area whereas great gap was rare. Metaphase gap was dominant in this area. Uprooting treefall was most in the Gap maker, and truncal basal breakage, fell stub, standing die were less. The least was middle-truncal breakage. Gap was mainly constituted with 1-3 gap makers including Q. liaotungensis and P. tabulaeformis. The probability of Betula platyphylla> Populus davidiana to become gap maker was less since distribution in canopy was limited. Most Diameter class of gap makers was under 30cm.4. The status of Q. liaotungensis renewal in Malan forest area was well but P. tabulaeformis was inferior. The mean density of Q. liaotungensis seedling and sapling was bigger than P. tabulaeformis while livability of P. tabulaeformis seedling was higher than Q. liaotungensis. Response rules of Q. liaotungensis and P. tabulaeformis regenerations for gap size and age had obvious difference that related to bioecology traits, mean coverage of shrub and herb in gap. Otherwise, gap regeneration ways of Q. liaotungensis and P. tabulaeformis in different forest community types were distinguishing. In the mass, Q. liaotungensis seedling had more capability for inhabiting in gap than P. tabulaeformis, further more, the trend that Q. liaotungensis may diffuse in P. tabulaeformis was observed. Gap appearance, development and dynamic cycle change with surroundings were possibly important microcosmic mechanism for plant community succession in Malan forest area.In our study, plant community secondary successional series were mainly natural recovery accompanied by human disturbance in Malan forest area on loess plateau. Recovery level of P. tabulaeformis pure forest represented for artificial forest was lower than that of Q. liaotungensis represented for natural secondary forest. Although in the natural recovery of degraded ecosystem, especially at initial stage, artificial forest could accelerate succession, species planted by human didn't show superior adaptability. Hence, the further investigation emphases were the degree of community recovery with natural force, species of artificial assistance planting, and species quantity with appropriate ways.