A Study On Decomposition Characteristics Of Needle Litter From Pinus Tabulaeformis Artificial Plantations Under Different Densities

Using the Pinus tabulaeformis plantations as the research objects, study the characteristics of litter decomposition in 3 ages pine plantation forests of 4 densities, for enriching and improving the plantation managements. The study used the litterbag technique to quantify organic concentration and the dynamics of inorganic nutrients in coniferous leaves, understand the density effects on litter decomposition rates of same-age-class Pinus tabulaeformis plantations under four different densities treatments with plots allocated in the middle hilly lands of Yingpan, Yanqing County, Beijing. Using analysis of variance(ANOVA), correlation analysis, regression analysis and other statistical analysis to study litter decomposition properties in different density forests and the density effects on litter decomposition. The results showed that:(1) Pinus tabulaeformis plantation litter mass loss rates showed the bimodal curve, the most quickly loss weight in September every year. After two year decomposition, the maximum mass loss rate in 24-year-old plantation forest is the treatmentâ…¡,51.75%; the maximum mass loss rate in 32-year-old plantation forest is the treatmentâ…¡,46.01%; the maximum mass loss rate in 41-year-old plantation forest is the treatmentâ…¢,74.56%.(2) Decomposition cycles of coniferous litter for Pinus tabulaeformis were different in different ages with various density forests. The average decomposition cycle in 24-year-old Pinus tabulaeformis was 8.79 years; in 32-year-old forest was 11.12 years; in 41-year-old forest was 5.55 years. The maximum decomposition rate was in every September. The two factors most directly influencing decay rates were both litter quality factors- the C:N ratio and the total nutrient content of the litter (the sum of concentrations of individual nutrents).(3) The dynamics of inorganic nutrients in litter showed the model of accumulation -release-accumulation -release. The releasement peak was every fall, the first Novermber to the next March was the nutrients accumulation period.(4) Correlation analysis which between litter decomposition coefficient and nutrients initial concentrations in the same age but different density forests showed that:The initial N content and initial C:N ratio were the main factors influence litter decomposition rates in early stage.(5) The optimal density in the three age forests were that:the highest decay rate in 24-year-old forest was treatmentâ…¡which was 1950 tree/hm2 and the decay rate constant (k) was 0.48; the highest decay rate in 32year-old forest was treatmentâ…¡which was 1925 tree/hm2 and the decay rate constant (k) was 0.31; the highest decay rate in 24-year-old forest was treatmentâ…¢(which was 1375 tree/hm2 and the decay rate constant (k) was 0.68.