Study On The Different Densities And Age Groups Chinese Fir Plantations The Net Primary Production And The Soil Organic Matter And Total Nitrogen Characteristics Of Jiangxi Province

This study was conducted at Nianzhu Forest of Dagangshan in Fenyi Country and Guanshan Forest of Yongfeng County, Jiangxi Province. By investigation and determination of different densities and different age groups of Chinese fir plantations, allometric equation and regression estimation methods were used to model and estimate the growth patterns, net productivity and soil nutrient characteristics of fir plantation ecosystem under different densities and different age groups. The main findings were as follows:1. The DBH (diameter at breast height) growth of Chinese fir plantation was affected by the stand density. Within certain range of density, DBH was increased with the decreasing density. Height growth was decreased with increasing density. The growth of Chinese fir individual volume was increased with decreasing density. With the decreasing density the growth duration of Chinese fir was tend to decrease. But the increasing rate and extent of different age groups were not the same. During10-15a, the DBH and tree height reached to quantitative maturity, while the volume reached to the quantitative maturity after35a.2. According to the allometric equation method, we used nonlinear regression to establish the biomass estimation model of Chinese fir with the different densities and different ages: Low density:w=2.531D2.065N-0.301(R2=0.981) High density:w=10.674D0.121N0.0001(R2=0.943) Different age:w=0.042D0.865A0.108(R2=0.967)3. According to the average basal area of law and individual biomass model, we estimated the total biomass of the stands with different densities and different ages. Coupled with understory biomass (including shrubs, herbaceous and litter), net productivity of Chinese fir plantation ecosystem under different densities and different age groups was estimated. The net primary productivity of Chinese fir plantation ecosystem in low-density stand was significantly higher than that in the high-density stand. The net primary productivity of Chinese fir plantation ecosystem in the highest density stand (1667trees·ha) reached to an average of8.24t/ha-a, whereas the net primary productivity in the lowest (5000trees-ha) stand was2.2t/ha-a. The size of the net primary productivity under low density followed by low-density,(1667trees-ha)(8.24t/ha-a)> low-density (2500trees-ha)(7.77t/ha-a)> low-density (1111trees-ha)(7.17t/ha-a), The size of the net primary productivity under high density followed by high-density (1667trees-ha)(3.97t/ha-a)> high-density (10000 trees-ha)(2.21t/ha-a)> high-density (5000trees-ha)(2.2t/ha-a). The highest net productivity of the Chinese fir plantation ecosystem across different ages is20(4.13t/ha-a) and22a (3.01t/ha-a). The order is20a(4.13t/ha-a)>22a(3.01t/ha-a)>36a(2.37t/ha·a)>26a(2.14t/ha-a)>6a(0.79t/ha-a).4. Through analysis and comparison of the soil organic matter and total nitrogen content features under different densities and different age groups of Chinese fir plantation, our results suggested that were significant between high density and low density stands. The soil organic matter content in high-density stands was higher than that in low-density stands. The soil total nitrogen was not significant between high density and low density stands. The soil organic matter contents of Chinese fir plantations across different ages were not significant. The total soil nitrogen contents of Chinese fir plantations across different ages were also indistinctively.