鄂尔多斯高原特有种四合木生长和繁殖的种群间变异与濒危机制

Interpopulation difference in growth and reproduction of endemic specie s Tetraena mongolica in Ordos Plateau

四合木为中国特有种 ,其分布区局限于鄂尔多斯高原的西部。为了认识四合木濒危的机制并为其保护提供理论依据 ,对四合木生活史的关键阶段——繁殖进行了野外研究。由于分布区内存在较大的生境异质性 ,并受到了不同强度的人类干扰 ,所以对不同生境条件下的 6个种群进行了取样。通过对四合木的营养生长和繁殖的比较分析 ,得出如下结论 :( 1 )四合木植株的基径和冠幅和高度与年龄显著相关 ,但是与基茎和冠幅相关性更大 ,冠幅可作为个体大小的测度估计种群的大小结构 ;( 2 )冠幅大小呈负偏斜分布 ,通过不同种群冠幅与年龄的相关分析 ,得出冠幅的增长速率随种群的衰老而减缓 ;( 3)四合木的冠幅与其果实量和种子量相关关系显著 ,随着冠幅的增大 ,四合木植株的果实产量和种子产量也相应增加 ,但是这种关系存在种群间差异 ;( 4 )四合木的大部分种群都处于衰老期 ,种群内个体的大小变异性很小 ,对于种群的生存有不利影响 ;( 5 )由于空间上四合木的大小结构以及反映四合木繁殖状况的植株果实产量、种子产量等参数在不同种群之间存在显著差异 ( P<0 .0 0 1 ) ,因此应对不同的种群采取相应的管理措施以促进种群的更新和续存。

Tetraenan mongolica is an ancient shrub endemic to China that has survived in an unglaciated part of Inner Mongolia. Its curren t range is restricted to the west of Ordos Plateau. T. mongolica was identi fied as an endangered plant, and its population size is still decreasing because it was used for firewood by shepherds and its buds were heavily grazed by their sheep. In order to assess the status of its existing populations, we examined the inter population differences in growth and reproduction of six populations of T. mon golica occurring in contrasting habitats in Ordos reserve, Inner Mongolia. The results obtained in this study are given as follows: 1) There were significant relationships between age and radius of base stem and crown size, while plant he ight was uncorrelated with age. Thus crown size could be used as a predictor of plant size to reflect the structure dynamics of T. mongolica populati ons. Th e growth rate of its crown decreased with age; 2) Most individuals of T. mongo lica concentrated in the large class of crown size, indicating that its popula tions were in unstable state. The relationship between crown size and age varied among six populations. 3) Fruit and seed production of T. mongolica varied significantly among the six populations (P<0.001), and was significantly det ermined by crown size. However, the relationships between fruit and seed product ion and crown size differed among the six populations. 4) Most populations of T. mongolica decreased in size, which is believed to be the result of a combin ation of poor natural regeneration caused by low fecundity and competition betwe en adults and seedlings, habitat destruction by human disturbance and heavy graz ing by sheep. In order to protect T. mongolica, managerial measures are obvi ously needed to promote its regeneration. In doing so, heavy grazing and other t ypes of habitat disturbance should be avoided in the protected areas.