Preliminary Analyzing the Effect of Returning Farmland to Grassland and Forest Project on the Ecological Function of Xigaz Valley Area

27 Mar Preliminary Analyzing the Effect of Returning Farmland to Grassland and Forest Project on the Ecological Function of Xigaz Valley Area

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Abstract

调查并分析日喀则地区退耕还草(林)工程实施后生态功能效应发现,退耕还草显著提高了植被总盖度和平均高度。退耕还草5年后外来物种增多,原播种老芒麦(Elymus sibiricus)的重要值降低,Shannon-Wiener 多样性指数和均匀度指数均增加,说明退耕还草使植被群落趋于稳定。随退耕还草时间延长,植被和土壤碳密度总体呈上升趋势,退耕还草5年后,植被碳密度比退耕初期增加331.81 g C·m-2。不考虑退耕初期因耕播时施肥的影响,并以退耕还草第3年的土壤有机碳为本底值,0～30 cm土层土壤有机碳密度从退耕3年后的2.74 kg C·m-2增加到5.06 kg C·m-2,土壤固碳速率为1.16 kg C·m-2·a-1。0～30 cm土壤全氮增加到2.98 kg N·m-2,比退耕1年和3年分别增加了1.60和1.64 kg N·m-2。退耕并禁牧后土壤趋于松软,地表植被覆盖物增加,土壤容重随退耕年龄延长而降低,土壤最大持水能力增大,特别是土壤0～10 cm最大持水量增加显著,5年后达52.37 mm,比第1年(44.48 mm)高7.89 mm。由于退耕还草时间较短,底层土壤容重及最大持水能力变化不大。

English Abstract

The effects of reverting farmland to grassland and forest project (RFGFP)on the ecological function of Xigaz area were investigated. Results showed that the project significantly increased vegetation coverage and average height of plant. After the restoration of 5 years, alien species increased, whereas the important value of original seeded Elymus sibiricus decreased. The increases of both Shannon-Wiener index and evenness index indicated that the vegetation community had a stable tendency. With the extension of the project, the carbon density of vegetation and soil showed an upward trend. At the fifth year after reverting farmland to grassland and forest project, the vegetation carbon densities of both above- and under-ground increased by 331.81 g C·m-2, soil organic carbon (SOC) density of 0～30 cm soil layers increased to 5.06 kg·m-2, the carbon sequestration rate of soil was 1.16(kg·m-2)·a-1 when taking the SOC of third years as a background value. The soil total nitrogen in 0~30 cm soil layers increased to 2.98 kg·m-2, and increased by 1.60 kg·m-2 and 1.64 kg·m-2 compared to the first and the third years after restoration, respectively. The soil became soft and ground litter increased after the restoration project. With the extension of restoration, soil bulk density decreased, whereas the maximum soil moisture capacity increased, the maximum soil moisture capacity of the 0～10 cm soil layer increased to 52.37 mm in the fifth year, increased by 7.89 mm compared with the first year (44.48 mm). The soil bulk density and maximum moisture capacity didn’t show significant change in the subsurface soil.