毛乌素沙地中国沙棘人工林早衰原因与特点

为了解中国沙棘人工林早衰的原因与特点，对毛乌素沙地的人工林与天然林进行比较研究。结果表明，天然林林地土壤含水率、有机质、全N及速效N含量显著高于人工林，林地生产力、分株生长量也显著高于人工林，但林分密度显著低于人工林；天然林年龄结构为金字塔形，人工林则为纺锤形;在影响林地生产力和分株生长量的因素中，土壤含水率起决定性作用。可见干旱缺水、养分贫瘠、密度过大均可导致人工林早衰，其中干旱缺水是主导因素；人工林早衰的主要特点在于分株变小（寿命缩短）、林地生产力降低、林分稳定性削弱。

Causes and Features of Hippophae rhamnoides ssp.sinensis Plantation Premature Aging in Mu Us Sandland

For knowing the causes and features of the premature aging of Hippophae rhamnoides ssp.sinensis plantation,we compared natural forests with plantations in Mu Us Sandland.The results showed that in the natural H.rhamnoides ssp.sinensis forests,soil moisture content and organic matter,total nitrogen and available nitrogen contents were significantly higher than those of plantations,no significant difference was found in soil physicochemical properties.The productivity and plant growth of natural forests were obviously higher than those of plantations,but stand density was lower than plantations.The age structure of natural forest was stable and to some extent,a little improved,while plantations were in recession.Soil moisture content was crucial that affected forest land productivity and plant growth.Therefore,drought,barren,density all could lead to premature aging of plantations,drought was the dominant factor.The main features of premature aging occurring in plantations were that the ramets became smaller,which would lead to a shortened lifespan,land productivity decreased,the stand stability weakened.