| Cunninghamia lanceolata (Lamb.) Hook. is one of the most important tree species for producing timber in south China, and plays a crucial role in forestry production in the region. But, along with an enlargement of the area in C. lanceolata plantations, replanting is increasing on sites where one or more rotations of C. lanceolata have been harvested. Concern about the potential of site degradation by C. lanceolata plantations is rising.In October 1996, long-term research was initiated in Xiayang State Forest Farm, Nanping, Fujian Province, China by Fan Shaohui et al to study the influence of retaining 5 different levels of harvest residue on the growth of a second-rotation plantation as well as the effect on soil properties. The study was established during clear felling a 29-year-old C. lanceolata plantation. The purposes are to look for potential of site degradation, and put forward the optimal management measures to maintain or increase the productivity of second-rotation plantations and sustain soil fertility. In this paper, base on studies conducted for 8 years by Fan Shaohui et al, the time series method is used to study the effects of site management treatments on growth and soil properties of 9-year-old, second rotation C. lanceolata plantations. The results are as follows:1. Residue treatments had significant effects on the growth of second-rotation Chinese fir stand at 1 to 4 years of age but had no significant effects at age 5 to 9, Nine years after treatments, trees grown in double slash treatment (BL3) were still the best. Trees grown in slash burning treatment (SB) were the smallest. But no significant differences of tree growth among different treatments were found.2. Soil properties were different at different sampling times. Three to 9 years after treatments, soil bulk density, total P and total K did not change greatly, but soil bulk density was greatly affected by soil moisture at sampling time. Three years after treatments, soil organic C, total N, pH value, hydrolysis N and available K at 0-10 cm soil layer increased compared with pre-treatment conditions, from then on decreased with sampling time, and went gown to their lowest values at 9 years after treatments.3. Three years after treatments, soil hydrolysis N and available K at 0-10 cm soil layer, soil hydrolysis N at 10-20 cm layer and available K at 20-40 cm layer increased significantly (P<0.05) compared with pre-treatment conditions.4. Six years after treatments, at 0-10 cm layer soil organic C decreased by 6.93% compared with pre-treatment conditions, while total N, pH value, hydrolysis N and available K increased slightly, but the differences were not significant. At 10-20 cm layer, soil hydrolysis N increased significantly (P<0.05). At 20-40 cm layer, all the soil properties decreased except for hydrolysis N increasing slightly, but the differences were not significant.5. Nine years after treatments, soil organic C, total N, pH value, hydrolysis N and available K at all the 3 soil layers went down to their lowest values. Compared with pre-treatment conditions, soil organic C, total N and pH value at 0-10 cm and 10-20 cm layers decreased significantly (P<0.05), and soil organic C and pH value at 20-40 cm layer decreased significantly (P<0.05) too.6. Nine years after treatments, soil property with the greatest change rate at 0-10 cm layer was organic C (decreased by 10.76%) compared with pre-treatment conditions, and at 10-20 cm and 20-40 cm layers was available K (decreased by 15,31% and 19.84%, respectively). 7. Compared to pre-treatment conditions, average organic C reserve at 0-40 cm soil layer reduced by 4.63%,10.34% and 8.43% at 3,6 and 9 years after treatments, respectively, and average total N reserve at 0-40 cm soil layer increased by 0.96%, decreased by 4.33% and 6.21% at 3,6 and 9 years after treatments, respectively.8. There were some effects of slash residue treatments on the soil properties. Except for significantly lower soil bulk density of 0-10 cm layer of BL3 treatment than that of SB treatment at 9 years after treatments, the differences of bulk density, total P and total K among different treatments at different sampling times were not significant.9. Three to 9 years after treatments, the more residue was retained, the higher the soil chemical properties (organic C, total N, pH value, hydrolysis N and available K) at different soil layers were. The soil properties were highest in double slash treatment (BL3) and lowest in no slash treatment (BLo).10. Three and 6 years after treatments, soil pH value of 0-10 cm layer in BL0 treatment was significant lower than those in BL3 and SB treatment. Six years after treatments, hydrolysis N of 0-10 cm and 10-20 cm layers in BL3 treatment were significant higher than those in BL0 treatment. Three years after treatments, available K of 0-10 cm and 10-20 cm layers in BL3 treatment were significant higher than those in BL0 treatment. Nine years after treatments, differences of soil chemical properties among different treatments were not significant.11. The decomposition rate of branches residual in logging slash was slow. Sixteen,32,56,84 and 96 months after harvest, the branches residual decompose to 71.21%,50.41%,35.28%,12.99% and 9.92% of the total initial weight, respectively.12. Based on tree growth and changes in soil nutrients, retention of slash from the first rotation plantation is recommended as the best management option. |
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