退化草原狼毒个体年龄判定方法及其种群年龄结构的研究

详细观察了内蒙古东部退化草原糙隐子草(Cleistogenes squarosa)群落内狼毒(Stellera chamaejasme)的根颈分枝形态及其生长发育特点，研究了狼毒种群的年龄结构．结果表明，狼毒个体实际年龄为“类二叉分枝(quasi-dichotomous branching)回数加2”；根颈上茎的残茬、枝痕和环状痕是确定根颈分枝回数的重要辅助特征．重牧、过牧、极牧3个放牧演替阶段内狼毒个体最大年龄依次为15、16和19龄．8龄级个体数最多，其年龄比分别为18．71％、24．20％和19．06％．重牧阶段缺失1和2龄个体；过牧和极牧阶段均缺失1龄个体．狼毒种群年龄结构为“初始衰退型”，存活曲线接近于“凸型”或DeeveyⅠ型．老龄组(13龄以上者)个体数在重牧、过牧、极牧演替阶段分别占4．83％、2．84％和14．02％．随着放牧干扰的加剧，狼毒种群年龄结构呈现老龄化趋势．

Judging method of individual age and age structure of Stellera chamaejasme population in degraded steppe

Based on the minute observation of branches morphology of root-crown of Stellera chamaejasme in Cleistogenes squarosa community and its growth characteristics,this paper studied the age structure of S.chamaejasme population,and an individual age judging method "the times of quasi-dichotomous branching plus two" was put forward for the first time.Remnant stubbles,branch trace,and annular trace on the root crown were regarded as important morphological features,and used to confirm the times of quasi-dichotomous branching.The results showed that the oldest individuals at three grazing succession stages (i.e.,heavy grazing,over grazing and extreme grazing) were 15,16 and 19 years old,respectively.Among all age classes,the numbers of eight years old individuals were the largest,and the age ratio was 18.71%,24.20% and 19.06%,respectively,at the different succession stages.There were no one- and two-year old individuals at heavy grazing stage,and no one-year old individuals at the other two grazing stages.The age structures of the populations were "early declining types",and the survival curves were similar to protuberant type or Deevey I type.The numbers of old age individuals (thirteen years old and more) at the three succession stages accounted for 4.83%,2.84% and 14.02%,respectively.The age structure of the population tended to aging with the increase of grazing intensity.