The Study Of Community Stability Of Main Type Plantations In Northern Shaanxi Loess Area

The artificial forest is the main part of soil and water conservation forest system and the stability of the plantations is the basis for the soil and water conservation and other ecological functions in Northern Shaanxi Loess Area. The purpose of this research is choosing out the most suitable species and direction of management in different site conditions. In addition, we explore the new method to measure the community stability of artificial forest. The main types of artificial forest at the age of forty in Wuqi County, Shanxi province were used for the study. The main factors affecting the stability of the community were analyzed based on the sample survey. Several indexes were chosen from these factors to build a comprehensive index system for the evaluation of community stability and the relatively stability of these communities was measured. In addition, the Pinus tabuliformis plantation which has the lowest stability was used as a sample to research the influence mechanism of climatic factors on the radial growth of Pinus tabuliformis. And a new method to measure the community stability was explored which based on the fluctuations of constructive species radial growth under the interference of climate change. The results showed that:(1)In the Semiarid Loess area, the stability of plantation and the reasonable stand density were different in different site conditions. On the site of shady and gentle slope, the Populus simonii and Hippophae rhamnoides mixed plantation have the highest stability, and the Armeniaca sibirica and Populus simonii mixed plantation and Armeniaca sibirica and Hippophae rhamnoides mixed plantation are much lower. These three types of plantation were recommended to use as the soil and water conservation forest. And their reasonable density in the mature stage were1000tree/hm2,700tree/hm2,600tree/hm2.The stability of Pinus tabuliformis plantation is the lowest in the all eleven plantations. If this plantation was built, the control of density was important. Its density in the mature stage was1000tree/hm2. On the site of shade and steep slope and sunny and steep slope, the Armeniaca sibirica and Hippophae rhamnoides mixed plantation has the highest stability and their reasonable density in the mature stage were500tree/hm2,400tree/hm2. The site of sunny and steep slope was difficult for the normal growth of artificial forest. The stability of Armeniaca sibirica plantation survived was low and the plantation has the trend of soil fertility decline and habitat drought.(2)Precipitation is the key limiting factor of the growth and stability of artificial forest in the Semiarid Loess area of Shanxi. The Radial growth of Pinus tabulaeformis is mainly limited by the precipitation before growing season. The radial growth significantly and positively related to the precipitation of the late rainy season in the previous year, precipitation of January and the effective precipitation(>10mm) of march. And also the radial growth significantly and negatively related to the average temperature of September and October in the previous year and the average temperature of May and August. The large density may lead to the radial growth of Pinus tabulaeformis dependent more on the precipitation of rainy season in the previous year.(3) The method of measuring the community stability by the fluctuation of radial growth of trees is suitable for the forests in the Semiarid Loess area of Shanxi. The Radial growth change of Pinus tabulaeformis plantation with high density can be1.6times larger than the change of precipitation. The community is extremely unstable. The result of the stability of Pinus tabulaeformis plantation of this method was same as the first method.