额济纳绿洲不同林隙胡杨根蘖的发生特征

额济纳绿洲在维持我国西北广大地区脆弱的生态平衡方面起着至关重要的作用.但目前由于水资源匮乏和水污染,以及人为干扰,该绿洲中胡杨林退化严重,更新主要依赖林隙中的根蘖形式的无性繁殖实现.从胡杨根蘖幼苗的发生和生长与林隙的特征关系着手,揭示胡杨根蘖更新的规律.在研究中,调查了胡杨林内不同林隙条件下,胡杨根蘖幼苗的密度、苗高和基径等生长状况,以及林隙内主要的环境影响因子,包括地被物、土壤条件、胡杨母株和人为干扰等.研究结果表明:在胡杨的根蘖幼苗生长过程中,苦豆子与土壤条件是主要的影响因子,苦豆子密度、人为干扰和周边大树数量对根蘖的基径和高生长具有显著的影响,但根蘖的发生的密度与苦豆子和土壤条件等环境因子的相关性却不显著.在分析原因中提出了根蘖发生机制的随机性与环境资源异质性的假说.

Development and growth of root suckers of Populus euphratica in different forest gaps in Ejina Oasis

Populus euphratica forests are the dominant ecosystems in Ejina Oasis, which play an important role in keeping the fragile ecological balance in the vast northwest areas of China. However, P. euphratica forests are undergoing severe degradation in recent years as a result of water shortage and pollution and human disturbance. Due to the failure of seed-originated seedlings, the regeneration of the forest mainly depends on the clonal growth of root suckers. In this study, we examined the relationship between the development and growth of root suckers and the environment factors in different forest gaps to gain a better understanding of the regeneration dynamics of this forest. The results of principal component analysis (PCA) indicate that environmental factors in the forest gaps can be classified into five components: the density of Sophara alopecuroides, soil moisture and compactness, size of forest gaps, human disturbance, and amount of P. euphratica adult individuals (DBH>15cm) at the edge of the forest gaps. However, the result of Spearman Correlation Analysis shows that these environmental factors have no significant influence on the density of P. euphratica root suckers. Therefore it seems that the root suckers of P. euphratica sprout randomly. Meanwhile, results of another Spearman Correlation Analysis suggest that the density of Sophara alopecuroides and human disturbance and the amount of adult individuals of P. euphratica have significant influence on height and basal diameter of root suckers. Based on our observation, we put forward a hypothesis of randomicity and resource heterogeneity to explain the mechanism in developing of P. euphratica root suckers. At the same time, we think that enormous tending to root suckers is indispensable to improve regeneration of P. euphratica forests.