Biodiversity Characteristics Of Eucalyptus Grandis Plantation In Different Site Types

Plantation often plays important roles in providing wood for human being, slowing the increased tendency of CO₂ concentration, increasing forest coverage and alleviating the relied degree to natural forest. However, many problems as biodiversity decline, land degradation, production reduction and groundwater table drop were also co-occurred in plantation. Including others, biodiversity has been documented as the core of the problems. How to exert the ecological function, meanwhile satisfy the wood need and increase economy, and consequently to sustainable development is always the focus in plantation ecology. Despite of many previous studies have taken biodiversity in eucalypt plantation into consideration, there were inconsistent conclusions in whether the biodiversity reduction caused by unreasonable plantation management. The reduced biodiversity might be related with the site condition, but little information has been available on. Therefore, to understand the effects of site type on biodiversity in eucalypt plantations, the characters of above/below ground biodiversity were studied in different Eucalyptus grandis plantations with different site types by field investigation and laboratory analysis. The results could provide important data for site selection and biodiversity conservation in sustainable management of eucalypt plantation. The results as follows:(1) Rich plant species were observed under the eucalypt plantation. There are 71 families, 158 genus and 193 species of vascular plant in the investigated plantations, dicotyledon plants dominated the plantations, 45 families, 81 genus and 90 species for terrace site, 61 families, 111 genus and 132 species for hilly site with middle-thick soil, 52 families, 99 genus and 118 species for hilly site with thin soil. Land use character influenced the species composition of plant understorey. The standing plant species reflected the origin of forest, as Camellia sinensis, Citrus reticulata, Cunninghamia lanceolata, et al. Terrace site was dominated by herbs, originated from farmland; hilly site was dominated from shrub and herb with ratio of 1:1, originated from barren, forest and tea garden. As the result of it, the closely forest similarity was observed between two hilly site, the weak one between terrace site and hilly site with middle-thick soil. The analysis of plant flora indicated that the distribution characters of genus and species were similar among the different forest lands. The results hinted that geographic analysis of genus could better reveal the nature of plant flora. The geographic distribution of plant genus under eucalypt plantations dominated by tropic and warm zone characters. Rich disconnected distribution types of genus were observed.(2) Understorey vegetation in eucalypt plantations could be divided into 14 community types, which mainly reflected the main types in the investigated region. According to classified results, community structure of eucalypt plantations included three types: "eucalypt + shrub + herb" accounted for 74.1% of total sampling sites, "eucalypt + herb" accounted for 22.2% of total sampling sites, "eucalypt + shrub" accounted for 3.7% of total sampling sites. "Eucalypt + herb" dominated the terrace site, and "eucalypt + shrub + herb" dominated two hilly site.(3) Low similarity of species composition was observed among different sampling plots in the same site type, indicating the diversity and complexity of forest origination. The plant species in the eucalypt plantation was mainly originated from the primary species and propagules in the site, and other spread propagules by wind, animal and human being from abutted ecosystems. The forest land distributed with block and enchased with farmland due to the special character of hilly. Biodiversity was limited by the land use characters of primary land. Predominated species contributed little in plantation species richness. Asymmetric species distribution implied the tendency of vegetation differentiation and succession. Alternanthera philoxeroides and Conyza bonariensis showed the frequently visibility in terrace site. Hicriopteris glauca, Mallotus barbatus and Rubus ichangensis were found in the hilly site with middle-thick soil, while Melastoma normale was found in the hilly site with thin soil. The results suggested that the majority of standing species was reliable to loss, and the composition of plant species would change by the standing planting modification in eucalypt plantations.(4) Species evenness was varied insignificantly among eucalypt plantations with different site types. Species richness was not varied between the eucalypt plantations with terrace site and hilly site with thin soil, but species richness in hilly site with middle-thick soil was significantly higher than that in terrace site and hilly site with thin soil. Biodiversity index in the hilly site with middle-thick soil was significantly higher than that in terrace site, whereas the biodiversity index was significantly different between the hilly sites with middle-thick and thin soil, and between the hilly site with thin soil and terrace site. The richness and biodiversity index of shrub were lower than that of herb in terrace site, but which in hilly site with both middle-thick and thin soil showed little differences between shrub and herb. Evenness of both shrub and herb was high in all of the three plantations, but little varieties among layers. The varieties of richness, evenness and biodiversity index of herb layer were not statistical varied among the plantations with different site types. Species evenness of shrub was not different among the plantations with different site types, but species richness was varied, and showed the order: hilly site with middle-thick soil > hilly site with thin soil > terrace site. In addition, although biodiversity index of shrub layer was not varied between the hilly sites with middle-thick soil and thin soil, their values were relative higher than that in terrace site.(5) Weak relationships even negative associations were observed among the plant species under eucalypt plantation, suggesting the randomicity of species. This implied that low vegetation stability of standing plantation could induce the changes of species composition. The interspecific relationships among species might be influenced by both canopy eucalypt and the land characteristics. Compared to shrub layer, herb layer hadlower stability. According to the result of x² test and Spearman rank correlations, shrubplants could be divided into 4 ecological groups and herb plants could be divided into 3 ecological groups.(6) Rhus chinensis, Hicriopteris glauca and Rubus ichangensis of shrub, and Melastoma normale Miscanthus sinensis and Artemisia argyi of herb had wider niche under eucalypt plantation than others. These populations had more survive opportunities, wider distribution scale with better ecological adaptation. Meanwhile, the species with narrower niche were liable to disappear since the species with wider niche could better occupy and use the limited resources. Inhibited the growth of species with wider niche or changed the status of environment resources could manual modified the present niche, wide the niche of the species with narrower niche, resulting more species existed in eucalypt plantation. (7) The macro fauna and mesofauna densities of dry types were higher in the eucalypt plantations with hilly site than that in plantation with terrace site, but mesofauna densities of wet types were lower in hilly plantation. Saprophagous animals dominated the soil animal group in all of the three plantations with different sites, while the ratio of phytophagous animals was relative lower, suggesting land structure still kept the good status after planting eucalypt. The index of density-population could indicate the diversity character of soil animal community in the plantations with different site types, showed the order as: hilly site with middle-thick soil > hilly site with thin soil > terrace site.(8) The significant varieties of bacterial communities were found among the plantations with different site types by PCR-DGGE, showed the order as: terrace site > hilly site with thin soil > hilly land with middle-thick soil. This was inconsistent with the soil animal biodiversity in the plantations with different land types. The investigated plantations had different microbial structure, which was contrary to the opinion that only special microbial communities could adaptive to the soil in the eucalypt plantation.In conclusion, the related land condition as soil depth and land use controlled the characters of above/below ground biodiversity in eucalypt plantation. The results suggested that preserving native vegetation with a number of areas and mosaic structure could play essential roles in increasing opportunities that species input, preventing the baffle of gene flow corridors among native vegetations in eucalypt plantation regions. The mosaic structure formed by native vegetation and eucalypt plantation would conserve the biodiversity in the regions of eucalypt plantations. However, little attention has been paid to the effects of mosaic development modifications (such as, the size of preserving patch, corridors between native vegetations, the size and scale of eucalypt plantation), plantation management, land quality and their synthesis on the biodiversity of native vegetation. Further study is urgently.