科尔沁沙地樟子松林降雨再分配特征

Characteristics of rainfall partitioning by Pinus sylvestris var. mongolica forest canopy in Horqin Sandy Land,northern China

以中国科学院乌兰敖都荒漠化实验站35年生樟子松人工林为研究对象,通过对降雨、穿透雨、树干径流和林冠截留的观测,研究樟子松林对降雨再分配作用,分析各部分产生的阈值,确定降雨有效补给量。结果表明：2015年5—9月共观测到降雨事件31次,呈现小数量、低强度的特征,樟子松林地穿透雨、树干径流和林冠截留分别占同期降雨量的69.28%、1.26%和29.45%。林地有效补给量为117.67 mm,占降雨量的70.54%。穿透雨随降雨量增加而线性增加,发生阈值为0.85 mm降雨量;树干径流与降雨量呈二次多项式关系,当降雨量达到2.44 mm时,产生树干径流;林冠截留随降雨量呈现幂函数关系,截留率随降雨量呈指数减少趋势。降雨再分配比例受降雨等级影响,当降雨等级为15~20 mm时,林内有效降雨比例最高（90.35%）。明确樟子松林降雨再分配特征和比例变化对理解降雨补给作用和林地衰退的水分机制具有重意义。

Water stress is regarded as one of the main reasons leading to the decline of Mongolian pine （Pinus sylvestris var. mongolica, MP） in Horqin Sandy Land, where the soil moisture main- ly comes from the rainfall. However, few studies have so far addressed the rainfall partitioning in MP forest in this region. In this study, a 35-year old MP forest in Ulanaodu experimental station was selected, the effects of MP forest on rainfall partitioning, the thresholds of components, and the effective rainfall recharge were analyzed by monitoring the rainfall, throughfall, stemflow and interception in the forest. A total of 31 rainfall events occurred from May to September of 2015, showing a characteristic of small rainfall amount and low rainfall intensity. The throughfall, stem- flow and interception accounted for 69.28%, 1.26% and 29.45% of incident rainfall, respective- ly. The amount of effective rainfall recharge was 117.67 mm, accounting for 70.54% of rainfall. The throughfall increased linearly with the increase of rainfall, and the occurring threshold was about 0.85 mm of rainfall. Meanwhile, the stemflow showed an obvious quadratic polynomial rela- tionship with rainfall, and the stemflow would occur once the rainfall was above the threshold 2.44 mm. Furthermore, the interception showed an obvious power function equation with the rain- fall, and the interception ratio presented an exponentially decreasing trend with increasing rain- fall. Additionally, the ratio of rainfall partitioning was affected by rainfall grade, and when rain- fall grade was about 15-20 mm, there was a supreme proportion （90.35%） of effective rainfall occurring in forest. These results are of signifi and the water mechanism of MP forest decline cance for understanding the rainfall recharge role in the semi-arid region.