西藏典型草地地上生物量季节变化特征

采用高寒草甸、高寒草原、高寒沼泽化草甸和温性草原4种西藏高原典型草地类型地上生物量定点观测数据，分析其地上生物量季节动态变化特征和生长规律。结果表明，高寒沼泽化草甸地上生物量最高，其中围网草地年均地上生物量达384.45 g·m-2，比无围网草地地上生物量高73%，且是温性草原类草地生物量的6倍，是高寒草甸和高寒草原类草地的12~14倍，与自由放牧相比，围栏禁牧措施可以明显提高草原地上生物量，是改良退化草地最有效的措施之一；温性草原草地生产力大于高寒草甸和高寒草原，城市附近山地草地生物量明显大于远离城市的地区，表明城市化进程降低了天然草地放牧强度，是恢复退化草地生产力的有效途径之一；属半干旱气候类型的西藏高原中部，降水是制约草地植被生长的主要因子；草地地上生物量的绝对增长速率和相对增长速率季节动态均在生物量达到高峰期前为正增长，之后为负增长。区域水热条件差异及其季节性变化导致了不同草地类型或同一类型不同区域的草地最快生长期出现的时间存在一定差别。

Seasonal dynamics of aboveground biomass of typical grassland types on the Tibetan Plateau

A study of four major grassland types (alpine meadow, alpine steppe, temperate steppe and alpine swamp meadow) in central Tibetan Plateau was carried out in 2004. And the seasonal variations of abovegraund biomass (AGB) and growth characteristics were analyzed. Results showed that the highest AGB occurred in fenced swamp meadow with annual mean AGB of 384.45 g·m-2, which was 6 times of temperate steppe and 12~14 times of alpine steppe and alpine meadow, and it was also obviously higher than unfenced alpine swamp meadow with 73%. Compared with free choice grazing, enclosure obviously increased AGB and was one of the most effective approaches to improve degraded grassland. The production of temperate steppe was higher than alpine meadow and alpine steppe, and the grassland AGB near urban areas was greater than areas away from urban region, and urbanization was an effective way to reduce the intensity of grassland use and to restore grassland productivity. As semiarid temperate climate zone, soil moisture was the main factor to constrain grassland vegetation growth in Tibet. Absolute growth rate (AGR) and relative growth rate (RGR) of four grassland types were positive before reaching to apex of the vegetation growth and negative after apex. Due to differences in hydrothermal conditions and their seasonal variations results in different fastest growing period of AGB for four grassland types.