五台山林线过渡带华北落叶松格局过程和尺度分析

林线过渡带作为气候变化的预警区,有很重要的研究意义,林线过渡带中人工林的生存与发展对自然保护区景观生态系统影响显著。选取五台山林线内占绝对分布优势的华北落叶松为研究对象。设置50m×50m样地,随机选取5个10m×10m样方进行群落物种信息收集,对乔木的胸径和位置信息进行调查,利用点格局方法和CSR(完全空间随机模型)、HP(空间异质性过程模型)、RL(随机标签模型)对华北落叶松的活立木和枯立木的格局过程进行0—25m尺度上的分析,结果发现:活的华北落叶松平均胸径在11.54cm,死的华北落叶松平均胸径是8.27cm,这个对于30年以上华北落叶松来说胸径值偏小,其生长慢的特点是和林线这个生境特点相适应的。华北落叶松枯立木的聚块很大,在0—15m上都是聚集分布;活立木聚块小出现在0—3m、和21m上。空间异质性过程模型模拟的格局与活立木实际格局差异检验不显著,说明空间异质性可以很好解释活立木格局的成因。随机标签模型模拟结果表明现有活立木和枯立木只在21m附近出现负相关,主要是负密度制约效应是导致的华北落叶松死亡的主要原因,而且对幼苗到幼树的影响最大。同时推测灌木和华北落叶松幼苗和幼树的种间相关作用与其死亡也有一定关系。

Spatial pattern and process of Larix principis-rupprechtii at different scales in the timberline ecotone of Mount Wutai

The timberline ecotone is important in climate change study as an early-warning region. The survival and development of planted forests at the tree line has significant effects on landscape ecosystems in natural reserves. Larix principis-rupprechtii, which has definite dominance on treeline of Wutai Mountain, was selected as the research target. A 50m×50m sampling plot was set up, and information about the species in the community were collected in 5 random quadrats (10m×10m) within the sampling plot, diameter at breast height (DBH) and location of trees were measured and recorded. Point pattern analysis and null models of Complete Spatial Randomness (CSR), Heterogenous Poisson (HP), and Random Labeling (RL) were adopted to analyze the pattern and process of the dead and surviving individuals of Larix principis-rupprechtii on 0-25m scales. The results of analysis were the following:According to DBH statistics, the average DBH of surviving trees was 11.54cm, and that of the dead trees was 8.27cm. As for the tree growth rate, the DBH of Larix principis-rupprechtii was smaller than that in other areas, and the slow growth was a result of adaptation to the timberline ecotone. Dead tree had larger clusters and aggregation at 0-15m scales, and surviving trees aggregated at the < 3m and 21m scales. The difference between the Heterogenous Poisson (HP) simulation pattern and the observed pattern for surviving trees was not significant, which meant that spatial heterogeneity explained the pattern of tree survival well. The Random Labeling (RL) simulation result showed that surviving trees had negative correlations with dead ones around 21m, and that mortality was caused by negative density dependence, especially for sapling trees. Meanwhile, results speculated that inter-specific interactions between shrubs and sapling trees had effects on tree death.