西藏藏北高原典型植被生长对气候要素变化的响应

选取西藏藏北高原西部高寒草原植被、中部高寒草甸植被及东南部高寒灌丛草甸植被 3 种藏北地区最典型的植被类型, 结合临近 3 个气象观测站的资料, 分析这 3 种典型植被类型地区 1999—2001 年旬平均气温、旬总降水量和 SPOT VEGETATION 卫星 10 d 最大值合成归一化植被指数 (NDVI) 变化特征以及 3 种典型植被基于 SPOT VEGETATION NDVI 的生长变化对旬平均气温和旬总降水量两个主要气候要素变化的响应关系。 结果表明: 藏北地区降水资源的空间分布特点是东南部向西北部逐渐减少, 气温则由南向北逐渐递减, 与降水资源分布相反, 蒸发量西部高, 东部低; SPOT VEGETATION NDVI 能够较为准确地反映 3 种典型植被生长变化特征, 所反映的植被返青期和枯黄期等重要植被生长阶段与由积温计算的植被生长特征基本一致; 藏北地区基于 SPOT VEGETATION NDVI 的植被生长变化与气温的相关系数明显高于与降水的相关系数 , 其中以那曲为代表的高寒草甸植被的 NDVI 与旬气温和旬降水总量的相关系数最大, 分别为 0.81 和 0.68 , 表明藏北地区由于海拔高, 气候寒冷, 气温对该地区植被生长的影响明显高于降水的影响, 即该地区植被生长变化对气温的响应程度明显高于对降水的响应程度 , 是植被生长的限制性因素; 不同植被类型对气温和降水两个要素的响应程度大小依次是高寒草甸、高寒灌丛草甸和高寒草原。

The Response of Typical Vegetation Growth to Climate Conditions in North Tibetan Plateau

Based on the scanned and georeferenced vegetation map of North Tibetan Plateau from 1:1000000 China Vegetation Atlas and grassland resource map of the North Tibetan Plateau,alpine steppe in the western North Tibetan Plateau,alpine meadow in the central North Tibetan Plateau and alpine shrub meadow in the eastern North Tibetan Plateau are selected as three most typical vegetation types in the North Tibetan Plateau.First,the climate conditions in North Tibetan Plateau are analyzed.Secondly,the ten-day mean temperature and precipitation and SPOT VEGETATION ten-day maximum composite NDVI(normalized difference vegetation index) of three typical vegetation regions from 1999 to 2001 are studied.Finally,the relationships between vegetation growth based on the SPOT VEGETATION ten-day maximum composite NDVI and the ten-day mean temperature and ten-day precipitation as two key climate variables that affect vegetation growth in these regions are analyzed.The spatial distribution of the precipitation decreases from southeast to northwest and that of the temperature decreases from south to north in the North Tibetan Plateau.Contrary to the precipitation,evaporation is higher in west than that in east in the North Tibetan Plateau.SPOT VEGETATION NDVI variations can represent the three typical vegetation growth patterns.In two important vegetation growth periods,the date of the green-up initiation and withering of vegetation represented by NDVI is consistent with the vegetation growth phases by calculating from accumulated temperature.The coefficients between NDVI and corresponding temperature from 1999 to 2001 in the alpine steppe is 0.66,in alpine meadow 0.81,and in alpine shrub meadow 0.79,while the coefficients between NDVI and precipitation in three different vegetation types are 0.53,0.68 and 0.54,respectively.It means that NDVI variations in the North Tibetan Plateau are more sensitive to the temperature than to precipitation.Because of the high altitude and frigid climate in the North Tibetan Plateau,the impact of the temperature on the vegetation growth markedly is higher than that of the precipitation.The temperature is the main confining factor for vegetation growth in the North Tibetan Plateau.Response degree of three typical vegetations to climate variations in the North Tibetan Plateau from high to low are alpine meadow,alpine shrub meadow and alpine steppe,respectively.