Characteristics Of Species Diversity Of Plant Communities In Malan Forest Region On The Loess Plateau

Abstract 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 is situated in the northeast of Xunyi County, Shaanxi province. It belongs to the south of Ziwuling in the middle part of the Loess Plateau. Choosing different plant communities 'in the typical sites of Malan forest area, the relationship among plant communities and the coupling relationship between plant communities and plant species diversity were studied by multivariate analysis of plant communities and their members.The results as follows:1. The plant species diversity of communities and the changes of soil fertility of Pinus tabulaeformis plantations forests at different ages were observed in Malan forest region on the Loess Plateau. The results were as follows: 1) the species richness, diversity and evenness of P. tabulaeformis plantation forests were becoming more and more as the restoration time. The largest species richness occurred after around 30 years' plantation forest. The biggest index of species evenness and dominance appeared in P. tabulaeformis forests after planting approximately 20 years'. 2) Practice of planting P. tabuIaeformis forests had changed the features of the plant community. The species composition and proportion were quite different from wasteland which had few Sorensen index with the species of P. tabulaeformis forests. P. tabulaeformis plantation forests at 22 years held the biggest Sorensen index with P. tabulaeformis plantation forests at 28 years. 3) Investigating changes of soil fertility in P. tabulaeformis plantation forests showed that the planting P. tabulaeformis forest contributed a lot to the soil fertility. The contents of organic matter and the available nitrogen of the soil in P. tabulaeformis plantation forests of 28 years were more than those of P. tabulaeformis plantation forests at other ages. The humus became thicker, the pH of soil increased, and the soil held more alkalescency with prolonging of planting age.2. The characteristics of species diversity were systematically studied by using the Richness index, Diversity index, Simpson index and Evenness index for the forest communities. The results showed that: 1) the total community diversity expressed that the species diversity of mixed forests was higher than that of pure forests, and the species diversity of artificial forests was the lowest. 2) The species diversity was decreased in order of shrub layer, herb layer and tree layer in all communities. 3) In the different community types, the species diversity index of tree layer was higher in P. tabulaeformis+Q. liaotungensis mixed forest and broad-leaf mixed forest. The species diversity index of shrub layer was higher in P. tabulaeformis+Betula platyphylla mixed forest, B. platyphylla forest and artificial P. tabulaeformis forest. The species diversity index of herb layer was higher in artificial Robinia pseudoacacia forest, B. platyphylla forest and Populus davidiana forest; the species diversity index of tree layer and shrub layer were lower in artificial R. pseudoacacia forest and artificial P. tabulaeformis forest. 4) The evenness index of the shrub layer was higher than that of the herb layer, and the evenness index of the tree layer was the lowest. The evenness index of tree layer of broad-leaf mixed forest was higher than other forest communities and that of artificial forest lower. The evenness index of shrub layer varies in small range. But in the herb layer, the evenness index was the highest in artificial R. pseudoacacia forest and the lowest in mixed forest. 5) The analysis ofβdiversity index indicated that large differences between the artificial R. pseudoacacia forest and other forest communities. It also showed that the species composition in Q. liaotungensis forest, P. tabulaeformis+B, platyphylla mixed forest and P. tabulaeformis forest were similarity with that in P. tabulaeformis+Q, liaotungensis mixed forest. 6) It is important to plan a mixed forest to replaced pure forest at the beginning of planting for building a community with high species diversity. Native tree species should be first choice when selected.3. Compared differences in plant species diversity between conifer (P. tabulaeformis) plantations and natural secondary forests showed that: The H' and S of tree layer were significantly lower in natural conifer forest than old conifer and secondary forest, but were not different compared with mid aged conifer forest .The H' and S of shrub layer were significantly lower in mid aged conifer forest compared with other forest types. The H' of herb layer have no significant different in four forest type. The evenness index (J') of tree layer of mid aged conifer forest was lower than other forest communities and its J' of shrub layer was highest although its richness of shrub layer was lower than in the other forest types.The analysis ofβdiversity index also indicated large differences between conifer plantations and natural forests. Although the tree layer species were similar in old plantation and natural conifer forests, it differed greatly between the natural conifer and secondary forest. The natural conifer and secondary forest species composition in shrub layer differed significantly from those in plantation and secondary plots. Tree species were significantly less common in plantations than in abandoned coppice forests. It also showed that the species composition in herb layer of different forest type were similarity.The management of P. tabulaeformis plantations alters the plant species composition considerably; the number of sub tall-tree species is increased in old aged conifer forest, especially species dispersed by animals. Plantation management appears to affect ecological processes through seed dispersal. From the perspective of management, the change in the structure and composition of the canopy in plantations could affect the behavior of dispersers and regeneration.4. The plant species diversity in ecotone of artificial P. tabulaeformis and broad-leaved forest community was studied using transect sampling method. The major results are as follows: (1)The species richness and Margalef index appeared to increased from artificial pine forest to ecotone forest, to broad-leaved forest. But Shannon-Weiner index, Simpson index and Evenness index in the ecotone (mixed coniferous and broad-leaved forest) were higher than those in contiguous communities (artificial P. tabulaeformis and broad-leaved forest communities). The high diversity in ecotone was contributed by high diversity of arbor layer. But no significant difference of species diversity occurred in shrub layer and herb layer for different communities. (2) In forest ecotone communities, the number of Quercus liaotungensis seedling was increased with the growing number of adult Q. liaotungensis trees. The number of P. tabulaeformis seedling in ecotone forest was more than that in artificial P. tabulaeformis forest. (3) Compared with the thickness of litter fall and humus layer in different communities, we found that litter fall and humus layer of ecotone were thicker than that of contiguous communities. It does reflect artificial P. tabulaeformis and Q. liaotungensis mixed planting made the soil fertility level upgraded. (4)The study showed that the afforestation of mixed forests with multiple tree species could increase the community diversity and stability. In order to set up communities with high species diversities, mixed forested should be planted to substitute for natural purebred forests with single species and landrace species should be given priority consideration.