额济纳胡杨种群年龄结构与树干空心分布特征

Population age structure and cavity distribution characters of Populus euphratica in Ejina

在黑河下游额济纳胡杨林自然保护区内的核心区与缓冲区分别设置了3个50 m×50 m的样地,对样地内每株胡杨进行调查获取野外数据,分析了核心区与缓冲区胡杨的种群结构、树干空心出现概率、发生规律及其与种群年龄结构的内在联系。结果表明:缓冲区胡杨径级主要集中于5～15级,以成熟和过熟林为主,种群处于衰退状态;核心区胡杨径级组要集中于1～5级,以青壮年胡杨为主,种群处于稳定增长状态。无论缓冲区还是核心区都出现了胡杨空心现象,但以缓冲区更为明显。当胡杨胸径<20 cm时,胡杨空心的出现概率为0。当胡杨胸径>75 cm时,空心出现概率则达到100%。胡杨径级介于4～15级时,空心出现概率与径级呈线性正比关系(R2=0.57),且空心直径与胸径也表现为正比的关系(R2=0.88)。以上说明出现空心以后,胡杨胸径越大(年龄越大),其空心直径也越大,空穴化程度越明显。胡杨空心的形成可能和其存储大量水分与盐分有关,树干空穴化对胡杨生存并没有显著的不利影响。

The trunk cavity of Populus euphratica is a widely observed phenomenon after tree growth to a certain age.Generally think such phenomenon is a manifestation of senescence.this study observed trunk cavity also appeared in young and mid-age groups.At present,few researches concerned in this issue and the reasons for the cavity were also no agreement.The aim of the paper is to reveal the general occurrence and the relation between trunk cavity and growth of Populus euphratica.Three 50 m×50 m vegetation plots were selected and monitored at buffer zone and core areas in Ejina Populus Reserve,the lower reaches of Heihe River,respectively.The study sampled some basic data,including height,diameter at breast height and crown size.The cavity of trees was sampled by growth cone.The drill holes at the center position of the trunk and the height is 1 m from the ground.Based on field investigation,the paper analyzed Populus population age structure,appearance probability and general occurrence pattern of hollow trees.The results showed that the diameter class of Populus mainly distributed 5 to 15 and the population was declining in buffer zone.On the contrary,the diameter class of Populus mainly distributed in 1 to 5 and the population was increasing in the core area.The appearance probability of hollow tress was 0 when the diameter at breast height <20 cm while it reach to 100% when the DBH>75 cm.The paper also fond not only the appearance probability of hollow tress,but also the diameter of the hollow core all have linear relation with DBH(correlation coefficient is 0.57 and 0.88,respectively).The formation of hollow trees likely linked to the massive water and salt,which stored in the trunk.The sampled trees were divided into two groups,one is hollow trees another is normal trees.The variance of crown and height between the two groups was analyzed by one way ANOVA under different DBH classes(15-20 cm,20-25 cm,25-30 cm,30-40 cm,40-50 cm).The analysis results presented that the value of normal trees' crown and height is slightly higher than the hollow trees' under the same DBH class,but the variance is insignificant in statistics.Based on the above analysis,the study concluded that the widespread hollow trunk phenomenon of Populus euphratica didnot make the tree growing worse.The possible causes were:(1) although the trunk became hollow,the function of xylem and phloem has not been significantly affected.So,the tree can normally transport the water and nutrients.(2)Because of the characteristics of clonal growth of Populus euphratica,the physiological integration between maternal plant and ramet make they can shared resources.