中文摘要：

调查宁夏六盘山2011年秋一场罕见的早雪造成的华北落叶松人工林受害情况,分析林分受害率与立地条件和林分结构特征的关系。结果表明：高海拔冲风地段和土层瘠薄立地的林分受害率偏大;高密度林分的受害率显著大于低密度林分,说明密度是影响林分抵抗雪灾能力的重要结构指标,但直接原因是林分密度增高导致林分高径比增大;当高径比在0.7～0.9时,样地出现受害,但受害率随高径比增大的增幅不大,当高径比大于0.9后,林分受害率随高径比增大快速升高,当高径比大于1.0后,林分受害率随高径比增大急剧升高;及时间伐降低林木密度,把林分高径比降到0.7左右并维持在0.9以内,是提高森林抵抗雪灾能力的可行营林措施。

英文摘要：

In this paper we investigated damage caused by a rare early-snow event at late autumn in 2011 on the Larix principis-rupprechtii plantation of the Liupan Mountains, Ningxia of Northwest China. The relationships between the stand damage rate, site conditions and stand structure were analyzed. It was found that the damage rate was significantly higher in the stands on the sites with high-altitude, wind-exposure and thin soil thickness. The damage rate of high-density stands was apparently higher than that of the low-density stands, which illustrates that the stand density is an important stand structure indicator that affects its ability against snow damage. However, the direct affecting factor should be the higher H/DBH （the ratio of tree height to the diameter at breast height） caused by the high stand density. When H/DBH was 0.7 - 0. 9, the stand might suffer from snow damage, but the increasing range of the damage rate with increasing H/DBH was slight. When H/DBH was higher than O. 9, the stand damage rate increased rapidly with increasing H/DBH. When H/DBH was higher than 1.0, the stand damage rate increased very rapidly with increasing H/DBH. Therefore, reducing the stand density to lower the stand H/DBH to around O. 7 through a timely thinning, and then maintaining it within 0. 9 would be a feasible silvicultural measure to improve the forest ability against snow damage.