祁连山北坡退化林地植被群落的自然恢复过程及土壤特征变化

采用长期定位观测的方法,研究了祁连山北坡退化林地人工抚育下2001-2008年间植被群落的自然恢复过程和土壤特征变化。结果表明:人为干扰消除后,退化林地群落环境逐渐优化,群落的科、属、种均明显增加,物种成员更替频繁;灌木和乔木物种出现后,群落垂直高度增大,群落结构出现成层现象;群落总体多样性指数呈不断增大的趋势,在空间结构上,Patrick丰富度指数、Shannon-Wiener多样性指数和Simpson优势度指数表现出:草本层>灌木层>乔木层的规律,而Pielou均匀度指数变化相反;土壤含水量、土壤有机碳和全氮含量随植被恢复均不断增加。在实施封育禁牧措施后,退化林地实现了由草本群落-灌木群落-乔木群落方向的快速演替,当恢复到早期的先锋乔灌混交阶段时,群落的物种组成、结构和多样性趋于复杂化,土壤性状也得到一定改善,显示出相对较好的适应性和恢复效果。

Dynamics of vegetation structure and soil properties in the natural restoration process of degraded woodland on the northern slope of Qilian Mountains, northwestern China

The natural restoration of woodland is important to explain the ecological process in forest ecosystem. It is significant implications to assess degraded woodland dynamics and ecological effects under artificial fostering approach in theoretically and practical for forest biodiversity conservation and sustainable management in semiarid mountains. Study site was located in the Han Quangou basin forest distribution zone in the Qilian Mountains of northwestern China. In this area, the wood of Picea crassifolia has been depleted after logging or grazing disturbance. The wood vegetation had been degraded and changed to shrub, grassland and scattered Betula-Populus secondary forests. In 2001 year, we have established 4 fixed observation plots (10m×10m) along the elevation 50m interval range from 2468m to 2736m. In each plot, we have chose 3 grids (4m×4m) for shrubs, 6 grids (1m×1m) for grasses, 2 grids (1m×1m) for soil. In August, we have investigated vegetation community characteristics including species number, community coverage, plant density, community height, species frequency and wood diameter at breast height (DBH>1cm) in different years woodland (from 2001 to 2008). The soil physical-chemical properties of investigated plot including soil bulk density, soil water content, soil organic carbon and total nitrogen were determined in indoor laboratory. In the study, changes in the species composition and relative important value (IV) of main species, community structure, species diversity and soil properties were analyzed by methods of variance analysis. The results showed that after human disturbance was forbidden, the habitation of woodland became well gradually within 8 years. From 2001 to 2008, the number of family, genus and species of plant community increased apparently. In the process of community succession, former species was replaced by the subsequent species frequently. The Betula platyphylla and Populus davidiana gradually become the constructive species. With shrubs and trees growing up, the vertical height increased, and community structure divided different layer from ground to community's top crest. From 2001 to 2008, biodiversity index of community increased. Patrick, Shannon-Wiener and Simpson indexes were different at different layer of community, and the order of three index among different layers (from high to low) was herb layer (HL), shrub layer (SL), and tree layer (TL). However, the order of Pielou index was tree layer (TL), shrub layer (SL) and herb layer (HL). Soil bulk density (SBD) decreased from (1.21±0.06)g/cm³ to (0.73±0.04)g/cm³. Soil water content (SWC), soil organic carbon (SOC) and total nitrogen (TN) increased with the woodland restoring. Fencing and forest ban can restore the degraded woodland vegetation in northern slope of Qilian Mountains. Beside the vegetative form, the key species (B. platyphylla and P. davidiana) and the improving of soil moisture and nutrient, which were the main factors of succession process of degraded woodland from herbage community to trees community. When the community was at the stage of mixed vegetation, the species composition, community structure, and diversity were more complex than those in other stages. At the same time the soil quality was improved by vegetation restoration ecological. Therefore, adaptation ability of vegetation was high in the mixed vegetation stage of shrub and trees, which showed a good restoring effect.