Study On Forest Community Growth And Dynamics In Xiaolongshan Nature Reserve

Located in western Qinling Mountains, Xiaolongshan Nature Reserve is inthe southeast of Gansu Province across eight towns and three cities of Tianshui, Longnan and Dingxi. As the largest forestry region in Gansu, Xiaolongshan Nature Reserveboasts of abundant plant varieties, reputed as the plant gene pool across temperate zone and subtropics. This paper studies growth and dynamic changes of four populationsin the reserve and provides theoretical basis for Xiaolongshan forest vegetation tending, regeneration and protection.Studies on population structure and regeneration mechanism are of great significance to explanations of population ecological characteristics, regeneration countermeasures,population formation and stability as well as succession changes. This paper replacesage structure analysis with DBH class structure and draws population age structure chart based on field investigation and analysis of quantity statistics and age compositionof reprehensive samples such as Platycladus orientalis(Linn.) Franco. Betula albo-sinensis.Castanea mollissima and Fraxinus platypodaOliv.Space-for-time substitution studiesare used to develop the static life table, combined with vanishing rate curve,survivalcurve and mortality curve in view of population density changes. Survival curves ofthese populations then undergo linear regression analysis in collaboration with linear regression equation. Index equation and power function are then used to test the significance degree. In addition, four survival functions are introduced to better illustrate population structure and dynamic changes. Research findings are as follows.1. Platycladus orientalis(Linn.) Franco population age structure shows growth form in significant pyramid structure. A large proportion of the young individuals, amongthe whole，the first age class number occupy36.2%,Its static life table suggests thatthe survival curve is basically of Deevey-Ⅱ type. The use of four survival functions leads to the survival characteristics of Xiaolongshan Platycladus orientalis(Linn.) Franco population, namely growth in the early stage, stability in the middle stage and decline in the late stage. Despite the high mortality about50%, the great number of platycladus orientalis seedlings guarantees the population’s dynamic regeneration.2. Betula albo-sinensisBurk population age structure is generally in bell structure.The4th age to12age class have more number of individuals，The minimum number of individuals is seen in the first stage occupy1.7%. The entire populationshows stable form during regeneration process. Analysis on Betula albo-sinensisBurk life table shows that its population survival curve is basically of Deevey-II type,which means the mortality of every stage is basically same.Both age structure and life table have indicated that Xiaolongshan Betula albo-sinensisBurk population is dominated by mature individuals. The seedling stage witnesses fewer individualsand the entire population suffers from poor natural regenerating state. Betula albo-sinensisBurk population remained relatively stable within a certain time,but with the time go by, the population will tend to aging.For this reason, Betula albo-sinensisBurk population protection requires strengthened artificial tending so as to promote regeneration and seedling growth. 3. Analysis on Castanea mollissima population age structure shows that it produces abundant young individuals in number and the age structure presents growing form.However, middle-aged and elder individuals accounted for less than20%, which means young individuals suffer from a low survival rate. Its life table analysis and survival curve suggest that the population survival curve is of Deevey-II type. The life table,survival curve, four survival functions and age structure are consistent with each other, all announcing the Xiao longshan Nature Reserve Castanea mollissima population seedling has highest mortality rate, so taking corresponding protection is necessary inCastanea mollissima growth process.4. Studies on Fraxinus platypodaOliv.population reveal that it has a complete pyramid age structure. Generally speaking, it is in growth form. Seedlings and saplings take a considerable proportion of the entire population, so the population brims with astronger natural regenerating ability and a similar age structure change to that of Platycladus orientalis(Linn.) Franco. Its static life table reveals its population survival curve to basically belong to Deevey-II type. Four survival functions introduced have also showed that Xiaolongshan Fraxinus platypodaOliv.population enjoys a strong ability innatural regeneration...