Abstract: 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 mainly 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, stemflow and interception accounted for 69.28%, 1.26% and 29.45% of incident rainfall, respectively. 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 relationship 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 rainfall, and the interception ratio presented an exponentially decreasing trend with increasing rainfall. Additionally, the ratio of rainfall partitioning was affected by rainfall grade, and when rainfall grade was about 15-20 mm, there was a supreme proportion (90.35%) of effective rainfall occurring in forest. These results are of significance for understanding the rainfall recharge role and the water mechanism of MP forest decline in the semiarid region.

Key words: climate change, geographic distribution., Southwest China, species distribution models, Gentiana rhodantha