荒漠草原人工灌丛化对蒸散发及其组分的影响——以盐池县为例

我国西北防沙治沙工程中大量的种植中间锦鸡儿(Caragana intermedia)会导致荒漠草原发生灌丛化现象,研究人工灌丛化对荒漠草原蒸散发的影响,不仅能够揭示半干旱区人为活动对生态系统水循环的影响机理,还可以指导区域生态治理实践。以宁夏盐池县荒漠草原为例,基于植被的生理生态参数和荒漠草原水热条件,采用生物地球化学模型(Biome Bio-Geochemical Cycles,Biome-BGC)和地球呼吸系统模拟模型(Breathing Earth System Simulator,BESS)结合的方法,模拟荒漠草原生态系统人工灌丛引入前后蒸散发及其组分的变化,定量研究荒漠草原人工灌丛化对区域生态水文循环中蒸散发的影响。结果表明,人工灌丛的引入使植被结构及特征发生了变化,叶面积指数(Leaf Area Index,LAI)年最大值由0.20增加为0.67,改变了植被年内与年际变化特征。荒漠草原人工灌丛化后,生态系统年均蒸散发由251.74 mm增加到了281.42 mm;人工灌丛化对生长季的蒸散发增强明显,8月蒸散发峰值时,日均蒸散发由1.27 mm/d增加到1.56 mm/d。灌丛化过程使生态系统蒸腾量平均增加了1.35倍,蒸发量增加了1.06倍,改变了生态系统蒸散发的组分结构,导致蒸发比例降低、蒸腾比例增高。由此可知,荒漠草原在防沙治沙和生态治理中大量种植灌木的现象,加大了区域生态系统的蒸散发,并改变了水分耗散结构,从而对生态系统地气水汽交换有较大影响,研究结论对荒漠草原生态治理及未来的植被重建有一定的借鉴意义。

Effects of planted shrub encroachment on evapotranspiration and its components in desert steppe: a case study in Yanchi county, Ningxia Hui Autonomous Region

Caragana intermedia, which is widely planted with implementing of the ecological engineering for combating desertification in Northwest China, has caused the phenomenon of shrub encroachment in desert steppe. Studying the effects of planted shrub encroachment on ecosystem evapotranspiration (ET) in desert steppe can not only reveal the mechanism how human activities change the water cycle of ecosystem in semi-arid areas, but also guide local government to implement ecological restoration and construction. Based on the physiological and ecological parameters of vegetation and the hydrothermal conditions of the desert steppe in Yanchi county, Ningxia Hui Autonomous Region, the Biome Bio-Geochemical Cycles (Biome-BGC) model and the Breathing Earth System Simulator (BESS) model were combined to simulate the evapotranspiration changes and its components with the planted shrub encroachment occurring in the desert steppe ecosystem. The effects of the planted shrub encroachment on regional evapotranspiration was also been evaluated by the simulated data. The results showed that the planted shrub in grassland has changed the structure and characteristics of vegetation, and the annual maximum leaf area index (LAI) increased from 0.20 to 0.67, which changed the interannual and intra-annual characteristics of LAI in the desert steppe ecosystem. The annual average evapotranspiration of the ecosystem increased from 251.74 mm to 281.42 mm with the planted shrub encroachment occurred in the desert steppe of Yanchi county. Planted shrub encroaching significantly increased the ecosystem evapotranspiration in desert steppe during the growing season. The highest daily evapotranspiration was in August, the average daily evapotranspiration of desert steppe ecosystem increased from 1.27 mm/d to 1.56 mm/d in this month during the planted shrub encroaching. Planted shrub encroachment in desert steppe increased the transpiration of ecosystem by an average of 1.35 times and the evaporation by 1.06 times, which reduced the proportion of evaporation in evapotranspiration and increased the proportion of transpiration correspondingly, and therefore changed the structure of ecosystem evapotranspiration. It can be concluded that the evapotranspiration of the regional ecosystem has been increased with a large number of shrubs planted in desert steppe for preventing desertification and recovering ecosystem. And these activities also changed the composition of water consumption in desert steppe and thereby had a great impact on the flux of water in the ecosystem. The conclusions of this research bring insight for ecosystem management and vegetation reconstruction in desert steppe in the future.