乌珠穆沁草原水热分配差异对植被的影响

The effect of water/thermal dynamics on Ujimqin grassland

利用MODIS NDVI数据和气象站点的气温和降水资料,运用最大值合成、一元线性分析和相关分析方法,分别从年际变化、季节变化和月变化角度分析2000—2013年乌珠穆沁草原植被覆盖变化及其对气温和降水变化的响应特征。结果表明,从年际变化看,近15年来乌珠穆沁草原植被覆盖呈增加趋势,其变化趋势主要受降水量的控制;从季节变化来看,夏季和秋季植被覆盖度呈上升趋势,而春季呈下降趋势。春季和夏季植被覆盖变化主要受降水的影响,而秋季植被生长与气温的关系较与降水的关系密切;从植被生长的月变化来看,NDVI与气温的相关性小,与降水量的相关性大。在返青期初期(4、5月)NDVI值随气温升高而升高,温度有助于植被的生长,其他时段气温对NDVI值产生负向作用,其中7月份植被生长受气温的负向作用最明显;4—6月受当月降水量的影响明显,7、8月份NDVI值与6月份降水量呈显著相关,表明植被生长对降水变化具有一定滞后性。

In this paper, MODIS NDVI dataset and corresponding climatic variables including temperature and precipitation were selected as the data sources to discuss the time series characteristics of vegetation change in Ujimqin grassland and the relationship between vegetation coverage changes and climatic variables from the yearly, seasonal and monthly time scales. The results indicated that the annual vegetation coverage had a tendency of increasing from 2000 to 2013 in Ujimqin and it was largely controlled by precipitation. In recent 15 years, the vegetation cover increased in summer and autumn, while decreased in spring. The correlation analysis between seasonal NDVI and corresponding seasonal climate factors showed that the precipitation was the main factor influencing vegetation cover changes in spring and summer, while the autumn was mainly affected by temperature. Correlation between monthly average of vegetation NDVI and climatic factors showed that the response of vegetation to precipitation was higher than that of temperature, while in April and May the correlation between NDVI and temperatures was stronger, indicating that the temperature was necessary in the early stage of vegetation growth. And in other period the temperature had negative effects in vegetation growth. The NDVI in July and August was significantly correlated with the precipitation in June, showing a hysteresis response of vegetation growth to rainfall.