海南霸王岭陆均松空间分布格局及其与微生境异质性的关系

应用地统计学及限制性排序分析方法,对海南霸王岭陆均松(Dacrydium pectinatum)幼苗、幼树、成树及其微生境因子的空间分布特征进行分析。结果表明:1)陆均松不同生活史阶段空间分布格局存在明显差异,幼苗阶段表现为聚集性分布,具有显著的空间自相关结构,聚集强度随年龄增长呈逐渐减弱趋势;2)RDA分析表明,陆均松空间分布格局与微生境因子的关系在不同生活史阶段存在差异,生境过滤的影响会随着生活史阶段的不同而有所差别;3)微生境变量对陆均松幼苗、幼树、成树空间变异的总解释量分别为78.4%、41.2%、33.6%,微生境因素对陆均松分布的限制作用主要集中在幼苗阶段;4)在大尺度条件下,PCNM变量与微生境变量具有较大的共同解释量(22.2%),存在典型的"诱导空间变差"现象,微生境变量空间变化引起响应变量即陆均松幼苗、幼树、成树的分布产生类似的空间结构。研究结果证实了微生境因子与不同生活史阶段陆均松分布的关联性,为深入理解陆均松种群维持机制、空间分布格局、更新动态与生境的关系提供科学依据。

The relationships between microhabitat heterogeneity and the spatial distribution of Dacrydium pectinatum in Bawangling, Hainan Island

Dacrydium pectinatum is the only Dacrydium genus of Podocarpaceae family in China. It is one of the symbolic species in tropical mountain rain forest in Hainan Island and one of the key species to maintain the natural communities in that region. Its distribution range is very narrow and it can only be found in the forest region of Bawang Mountain, Jianfengling Mountain and Diaoluoshan Mountain. From the beginning of 1960s, the natural forest of D. pectinatum has been severely damaged because of people''s massive logging of tropical forests in Hainan. As a result the distribution area of D. pectinatum has become ever smaller, the quality of D. pectinatum forest has gotten ever worse, and it has become ever harder for the D. pectinatum to naturally regenerate themselves. What''s worse, there has emerged a decline in tree-age structure. Based on this situation, D. pectinatum was listed in China Rare and Endangered Plants Red Data Book as the third degree of endangered plants in 1992. The paper first defines the three stages of D. pectinatum growth based on its diameter at breast height and tree height. Specifically seedling is defined as the tree with a height under 50 cm, sapling refers to the tree with a DBH lower than 10 cm and a height over 50 cm, and matured trees are those whose DBH are larger than 10 cm. The paper used geostatistics and constrained ordination analysis method to analyze the space distribution characteristics of D. pectinatum in three life stages from the perspective that there is relevance between its space distribution in different life stages and microhabitats factors. Also, the spatial autocorrelation of 11 microhabitats is analyzed. The results showed that: 1) there was an obvious difference in the spatial distribution of D. pectinatum in its different life stages. The seedlings were in aggregating distribution and lived with significant spatial autocorrelation. However, the aggregating intensity gradually weakened with the seedlings growing into sapling and then to matured trees; 2) RDA analysis showed that there were significant differences in the relationship between the distribution patterns and microhabitat factors in different life stages of D. pectinatum, and the effect of habitat filtering varied with the change in its life stages. 3) The effect of microhabitat variables on the spatial variability of the seedling, the sapling, and the mature trees were 78.4%, 41.2%, and 33.6%, respectively. In the whole life stage, the period from the seedling to the sapling is the key to successful plant colonization. And seedlings have got stronger environmental sensitivity than the adult tree. It follows that the restrictive effect of microhabitat factors on D. pectinatum''s distribution mainly occurred in its seedling stage; 4) In sound conditions, 22.2% variation can be interpreted by PCNM variables and microhabitat variables in common. And a typical ''induced spatial variation'' phenomenon was found, which means that the spatial variation of microhabitat variables can result in the spatial variation of D. pectinatum throughout its seedling, sapling stage and matured stage. The results confirmed the relevance between microhabitats and the distribution of D. pectinatum in different life stages. And the paper provided a scientific foundation for better understanding of the relationship between the mechanisms of population maintenance, the spatial distribution pattern of D. pectinatum, and its regeneration dynamics. If there will be any further research on this topic, it is suggested that the monitoring and the study be carried out during a longer time span, and larger size of sample be studied, for a more accurate analysis of the influence of microhabitat factors on seedling regeneration and its survival pattern.