Effects Of Slash Management Treatments On The Productivity Of A Second-rotation Chinese Fir (Cunninghamia Lanceolata) Plantation

Over the last 40 years, the area of world forest plantation continuously increases, but rotation of forest plantation was shortened, in case eucalyptus pulp woods, rotation shortens to 5⁷ year. But forest plantation base needs over a long period of time the steady management, Hence the land degradation to research and the forest plantation soil fertility maintenance has turned into the focus that whole world forestry scientist concerned. In southern mountain area of our country, the pure coniferous forest proportion was up to 95% in the forest plantation, in it Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) forest plantation occupies forest area 1/3 up the south forest area, But Chinese fir (C. lanceolata) forest plantation soil fertility maintenance capability was bad, Management history was too short, But constantly continuous plantation, the land degradation was more serious.In view of the land degradation of the Chinese fir forest plantation, objectives of this study were to measure the influence of several site management treatments on long-term productivity of Chinese fir (C. lanceolata) plantation after a rotation. A second rotation C. lanceolata plantation was established with five site preparation treatments on the cleared plots of first rotation C. lanceolata. The experiment result shows:1. Residue treatments had significant effects on the growth of second-rotation Chinese fir stand at 1 to 5 years of age but had no significant effects at age 6 to 8. Eight years after treatment, trees grown in double slash treatment (BL3) were the best, those diameters at breast-height, height and stem volume were 14.39 cm, 9.48 m and 0.699m³stem^-1, but no significant differences of productivity of different treatments were found. The annual growth amount of height and diameter of trees reduced 20%³0% for the drought of 2003; the timber volume amount reduced 40%. Overload stem density of first rotation might reduce the productivity of second rotation, but it needed to be verified.2. Compare with the first rotation Chinese fir; undergrowth vegetation after one year of trial had changed greatly. Annual herb, perennial herb, and other intolerant plants' number and importance value increased in magnitude. But fern and other shade-tolerant plants' number andimportance value decrease in magnitude. After one year of trial, the composition of undergrowth vegetation was different among different treatments. The difference was mainly between slash burning treatment (SB) and the other 4 treatments with non-burning. In SB treatment, annual herb's species proportion was 19%, importance value was 28.02, and they were both higher than the other 4 treatments, but fern's species proportion was 14%, importance value was 14.14, and were both the lowest among all the treatments. The importance value of deciduous shrub was 11.50, also higher than the rest of the other treatments.3. Soil properties were different at different sampling times. Three years after treatment, soil bulk density reduced 0.03 g-cm"3 at 0¹0 cm soil layer, but soil bulk density of 10-20 cm and 20-40 cm soil layer slightly high than those before treatments. Soil bulk density slightly reduce at 6 years of age.Three and 6 years after treatment, soil pH value slightly increased at 0-10cm and 10-20cm soil layers, but slightly reduced at 20-40 cm soil layer.Three years after treatment, organic C slightly increasing at 0-10 cm soil layer, but reduced 10.73% and 7.42% at 10-20 cm and 20⁴0 cm soil layers, respectively. Six years after treatment, organic C slightly decreased in all layers, but at 10-20 cm and 20-40 cm soil layers slightly increased than three years after treatment.Three and 6 years after treatment, total N slightly increased at 0-10 cm soil layer, but organic carbon reduced at 10²0 cm and 20-40 cm soil layers.Three years after treatment, average organic C content reduced 4.63% at 0-40 cmsoil layer, and six years after treatment, average organic C content reduced 10.34% compared to pre-harvest conditions. Three years after treatment, total N content increased 0.96% at 0-40 cm soil layer, but 6 years after treatment, total N content reduced 4.33% compared to pre-harvest conditions.It was significant differences between soil hydrolysis N and available K at different sampling times.Three years after treatment, at 0-10 cm, 10-20 cm and 2040 cm soil layers, hydrolysis N increased 21.48%, 13.95% and 7.87%, respectively. Six years after treatment hydrolysis N was lower than three years after treatment, but also increased 7.08%, 11.58% and 5.62%, respectively, compared to pre-harvest conditions.Three years after treatment, at 0-10 cm, 10-20 cm and 20-40 cm soil layers, available K increased 50.50%, 21.25% and 25.07%, respectively. Six years after treatment, available K significantly reduced at all soil layers than three years after treatment, but 5.34% higher at 0-10 cm soil layer than pre-harvest level, and decreased at 10-20 cm and 20-40 cm soil layers by 8.16% and 10.25%, respectively, than pre-harvest levels.There were significant changes of available K at the different sampling times. Three years after treatment, total P and total K slightly increased at all soil layers in different sampling times, but slightly reduced at six years after treatment, but were also little higher than pre-harvest level. But no significant difference was found beween the treatments.The only soil property being significantly affected by various treatments was the pH value at 0¹0 cm surface soil layer. Three and six years after treatment, soil pH value at 0-10 cm soil layer of no slash treatment (BLo) were significant lower than those of double slash treatment (BL3) and stem and bark harvest and slash burning treatment (SB). Retention of slash from the first rotation plantation could increase soil pH value, and reduce soil acidity.Three and six years after treatment, organic C and total N content were the highest in double slash branches treatment (BL3), but no slash treatment (BLo) or stem and bark harvest and slash burning treatment (SB) were the lowest, but no significant differences were found.Three and six years after treatment, organic C and total N content slightly increased or decreased at 0-10 cm soil layer only in stem and bark harvest treatment (BL2) and double slash treatment (BL3), but decreased significantly in the rest of the other 3 treatments.Three years after treatment, hydrolysis N was no significant difference at 0-10 cm and 10-20cm soil layers between different treatments, but six years after treatment, hydrolysis N of double slash treatment (BL3) was significant higher than those of no slash treatment (BLo).Soil available K was significant affected by different treatments. Three years after treatment, soil available K at 0-10 cm and 10-20 cm soil layers in double slash treatment (BL3) were significantly higher than no slash treatment (BLo).Soil total P and total K were little affeced by different treatments. No significant differences of soil total P and total K at all soil layers were found among different treatments.4. Decomposition rate of harvest residual was high in initial stages (0-16 months), and after 16 months, the decomposition rate decreased. The decomposition rate of leaves harvest residual was high. It took 16 months for the leavs harvest residual to decompose to 7.35% of the total initial weight, and followed the linear relationship. The decomposition rate of branches residual...