The Effects Of Thinning On Litter Decomposition Of Pinus Tabulaeformis Plantation

Pinus tabulaeformis is a main afforestation species in the northern China. Due to increase of the forest age and delay of tending and thinning measures, the return of nutrient elements in Pinus tabulaeformis litter is decrease, hence soil fertility tend to degradation in Pinus tabulaeformis plantation. The research subject of this paper is to study the effect of thinning intensity on decompositon rate of leaf litter and finally on soil fertility. We selected three different ages of 18-years, 25-years and 32-years Pinus tabulaeformis in same site class and carried out 4 thinning intensity respectively. The weight loss rate and the return of N, P, K, Ca, Mg in litter of Pinus tabulaefomis plantations were observed, the indexes of the soil fertility were measured, included physical properties, chemical properties and soil enzyme activity. Soil fertility are estimated by principal components analysis. The results show that:1. Along with the increasing of forest age, decomposition rate of Pinus tabulaeformis leaf litter is decreasing, the content of soil organic matter, total nitrogen, available phosphorus decrease obviously, The activity of the urease enzyme, alkaline phosphatase and catalase is also decreased. Soil fertility tends to declines.2. Moderate thinning can minish the ratio of lignin/ nitrogen and C/N, increase the decomposition rate of inus tabulaeformis leaf litter and nutrition return, increase the activity of the urease enzyme, alkaline phosphatase and catalase, accelerate the decomposition rate of litter chemical components such as lignin.3. The ratio of lignin/nitrogen and C/N is the main factor to restrict the decomposition rate of litter. These factor can estimate the decomposition rate of litter directly and the effect of thinning and soil fertility indirectly.4. Soil fertility are integrately estimated by principal components analysis based on soil physicalproperty, chemical property and enzyme, the score rank is in the same order as decomposition rate of litter, in the approximately same order as total nutrient return. So nutrient return in litter is the main factor affected on soil fertility. Choosing the appropriate thinning intensitis is the effective measure to release soil degradation of Pinus tabulaeformis plantation.