干旱区多枝柽柳的生长特性

多枝柽柳是分布最为广泛的柽柳属植物之一。也是维持干旱区荒漠生态系统的关键植物种。本研究运用树轮年代学和树干解析方法。对额济纳地区不同生境条件下多枝柽柳的年轮生长、高生长和地径生长等方面的特征进行初步探讨。多枝柽柳每年形成1个年轮。树盘偏心生长极为普遍．完整树轮大多在10龄以内区域，10龄以外都呈单个或多个不完整年轮生长区。多枝柽柳单枝在1～4年高生长缓慢．4～8龄之间属于快速生长期，10年以上生长速率急剧下降。不同地下水位条件下三组样本径生长年增长速率达到极大值的年龄分别为21、56和74年，水环境条件是影响多枝柽柳径向生长的主要因素。同一年年轮宽度随枝高呈减小趋势。多枝柽柳边材的树轮数一般在3～5轮之间，进入老龄阶段有增加趋势。边材宽度随年龄增长逐渐减小。

Growth Characteristics of Tamarix ramosissima in Arid Regions of China

Tamarix ramosissima,one of the most widely distributed plants of its genus,belonged to the key species for maintaining desert ecosystems in arid regions of China.The study adopted dendrochronology and stem analysis to preliminarily exmine such characteristics of Tamarix ramosisssima as annual rings,shoot heights and radial growth under different environments appearing in the Ejian region.It formed one annul ring every year,and commonly presented eccentric below-canopy area around its trunk;Tamarix ramosissima formed complete tree rings within ten years old and one or multiple incomplete tree rings beyond ten years old.Tamarix ramosissima shoots appeared to grow slow within 1~4 years old,quickly within 4~8 years old and at a sharply decreased rate beyond 10 years old.The maximum rates of Tamarix ramosissima radial growth appeared at the ages of 21,56 and 74 years in the three sample quadrats at the three water tables and thus water conditions were the major factors affecting Tamarix ramosissima radial growth.In same years,the tree-ring widths of Tamarix ramosissima shoots increased as the shoot positions went upwards.The tree ring number of Tamarix ramosissima sapwood generally turned out to be 3~5 but tended to increase in aged stage,while the sapwood width of Tamarix ramosissima gradually decreased with increased ages.