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The central Sichuan hilly area is one of the heaviest eroded region in the upper reach of Yangtze rive.In order to mitigate the soil loss and enhance water conservation,large mixed plantations between cypress and alder were established starting from 1960s.However,alder gradually disappeared with stand succession,and the plantations developed into cypress monoculture that is characterized by irrational structure,poor natural regeneration,poor stand stability and low ecological functions.In order to adjust the structure of cypress monoculture and improve its ecological functions,transformation experiment with different cutting intensity(cutting and replanting in different bandwidths) have been carried out from 2005.Canopy interception,water-holding of ground cover,soil water storage and surface runoff and sediment yield were studied in the transformation experiment.The results have shown that:(1) after stand transformation,canopy interception reduced,the total rainfall interception and interception per rainfall from 2010 to 2011 ranked from higher to lower as: the contrast(without cutting) 10 m bandwidth 8 m bandwidth 6 m bandwidth 4m bandwidth,and the differences among them were significant.(2) Transformed stands promoted the development of the shrubs and grasses;fresh biomass and water-holding capacity of shrubs and grasses were significantly higher than the contrast.The shrub biomass ranked as 8 m bandwidth 10 m bandwidth 6 m bandwidth 4m bandwidth the contrast(without cutting).The grass biomass in 8 m bandwidth is the highest one((9.93±0.56)t/hm2) and the lowest one occurred in 4m bandwidth((7.10±0.11)t/hm2).(3) The biomass and water-holding capacity of litter reduced after transformation,the total biomass and water-holding capacity of litter was significantly lower than the contrasts((1.28±0.081) t / hm2 and 0.36 ± 0.019mm).(4) Soil porosity and water retention in the transformed stands were higher than the contrast;but significant difference to the contrast only occurred in 8 m and 10 m bandwidths.(5) The total surface runoff depth of the contrast was very significantly lower than the transformed stands;the total sediment yield of the contrasts(1262.52kg / hm2) was significantly higher than the transformed stand(499.25—484.95 kg/hm2);but there was no significant difference among the different transformed bandwidths.By comparison,8m bandwidth is the most suitable one in cypress transformation. |
