在土壤侵蚀严重的黄土丘陵沟壑区，植被恢复重建是控制土壤侵蚀的关键，而种子是植被恢复的基础，也是植被恢复最敏感的阶段之一。土壤侵蚀与产沙的过程，不仅分散、剥蚀和搬运泥沙，同时还可将散落到地表的种子和土壤中原来保存的种子移走，造成土壤表面和土壤内部种子的流失。为此，利用人工降雨模拟试验，分析了不同雨强与坡度组合条件下产流产沙过程中的种子流失与迁移特征，研究了雨强、坡度及种子形态对种子流失和迁移的影响，得出以下主要结论：

1）种子随降雨产流产沙的流失过程大致可分为三个阶段：降雨前期种子流失相对较低阶段、降雨中期种子持续流失阶段和降雨后期种子流失不再增加阶段。当径流与产沙增加到一程度时，坡面开始有种子流失；随着降雨的进行，种子流失量随着径流与产沙量的增大而持续增加；而降雨后期，易流失的种子已基本流失，未流失的种子受其自身抗蚀策略的影响而不再流失，种子累积流失率趋于稳定。

2）在同一坡度下，降雨强度对种子流失的影响表现为降雨强度越大，种子开始流失的时间越早，种子的流失率越高。在50mm/h的雨强条件下，坡度为10°、15°、20°和25°的坡面上基本没有种子流失现象发生，而同一坡度下雨强为150mm/h时的种子流失率明显大于雨强100mm/h条件下的流失率。降雨强度对种子迁移的影响表现为降雨强度越大，坡面上尚未流失的种子发生位移的种子物种数越多，迁移距离越大。双因素方差分析表明雨强为影响种子流失和迁移的主要因素，但降雨强度对不同物种流失的影响程度不同。

4）不同物种种子的形态特征也显著影响着自身在坡面降雨侵蚀过程中的流失与迁移，但不同物种的种子，影响其流失的形态特征各不相同。有的主要是受种子重量的影响，如山杏、黄刺玫、平枝栒子；有些是种子形状起主导作用，如鬼针草，狼牙刺、侧柏；有些则受种子附属物的影响，如灌木铁线莲、异叶败酱、达乌里胡枝子；还有些种子的流失同时受比表面积和附属物的影响，如白羊草和阿尔泰狗娃花。种子重量是影响种子流失的主要因素，其次是种子的形状和附属物等。

5）供试物种如平枝栒子、小麦、柠条、茶条槭、鬼针草、大针茅、灌木铁线莲、刺槐、败酱、茜草和侧柏的种子，在降雨强度为100mm/h条件下具有一定的抵抗降雨侵蚀的能力，流失率为0～25.83%；而黄刺玫、山杏、山荆子、酸枣、枣、大豆、玉米和香青兰的种子即使在降雨强度为150mm/h时的侵蚀条件下，也不会发生流失。

Vegetation restoration is the key factor of soil erosion control，especially on the hilly-gullied Loess Plateau. Seed is the base of revegetation, also is one of the most sensitivity phase of revegetation. During Soil erosion process, seeds on the surface and buried in soil could be carried away at the same time. Thus, the experiment was designed to analyses the seed loss and movement during runoff and sediment yielding process under different rainfall intensities and different slope gradients combination by simulation rainfall. The influence of rainfall intensity，slope gradient and seed morphology on seed loss and movement were studied, and the main results are as follows:

   1）Seed loss during the process of rainfall erosion could be divided into three phases: low seed loss at the beginning of rainning, seed loss and removal increasing continuously in the middle of rainning , and seed loss no longer increasing in the late stage of rainning. when runoff volume and sediment yield increase to a some extent, some of seeds begin to move down slope; as the rainning going on, the seed loss ratio increases continuously with runoff volume and sediment yield increasing; in the late period of rainning, the accumulative seed loss ratio tends to be stable, that is because the seeds easily moved have lost, while those remained in slope would not loss for thier ecological strategies against erosion.

2）Under the same slope gradient, the heavier rainfall is , the earlier seed loss, the higher seed loss ratio is. When rainfall intensity is 50mm/h, there is hardly any seed losing in the slopes with gradient of 10°, 15°, 20° and 25°. However, the seed loss ratio under rainfall intensity of 150mm/h is more higher than that under rainfall intensity of 100mm/h. Moreover, the influence of rainfall intensities on seeds remain on slopes is that, the heavier rainfall is, the more species moving are, the longer distance of movement are. The two way ANOVA analysis showed that rainfall intensity is the main factor effecting seed loss and movement, But the influence of rainfall intensity on different species is different.

3）Under the same rainfall intensity, slope gradient has no significant influence on seed loss and movement, but different species have different feature on seed loss and movement. under the 100mm/h and 150mm/h rainfall intensity, Heteropappus altaicus, Lespedeza davurica, Periploca sepium and Bothriochloa ischaemun have a high seed loss ratio on the 4 slopes; The seed loss ratio of Bidens tripartita，Daucus carota and Patrinia heterophylla is much higher on the slopes with gradient of 10° and 15°. However, Cotoneaster horizontalis and Robinia psendoacacia have the most lowest seed loss ratio on gradient 10° slope. There is no seed loss of Dracocephalum moldavica, Armeniaca sibiriea and Rosa xanthina on any slope. Also, slope gradient has no significant influence on seed movement distance, but seed morphology of the species, seed loss ratio and other interfering factors may have effects on seed moving.