八大公山常绿落叶阔叶混交林影响幼苗存活的主要因子分析

Analysis of main factors affecting seedling survival in Badagongshan evergreen and deciduous broad-leaved mixed forest

幼苗是植物生活史中最脆弱的阶段,对幼苗存活影响因子的分析有助于我们更清楚的了解森林群落的天然更新机制。利用广义线性混合模型(GLMM)对八大公山常绿落叶阔叶混交林中影响幼苗存活的主要生物与非生物因子进行了研究。结果表明:(1)在群落水平上,幼苗存活与生物因子中的同种幼苗密度呈显著负相关,与非生物因子中的冠层开阔度呈显著正相关;(2)从年龄上看,4年生以下龄级的幼苗存活更容易受到同种幼苗密度的影响,与同种幼苗密度呈显著负相关;4年生及其以上的幼苗存活则主要受非生物因子影响;(3)从生活型上看,相对于常绿物种,落叶物种的幼苗存活率更容易受到同种幼苗密度的影响,也与冠层开阔度呈正相关;(4)在物种水平上,生物因子与非生物因子对不同物种幼苗存活率的影响也不相同。其中,宜昌润楠(Machilus ichangensis Rehd.et Wils.)的存活率与冠层开阔度呈正相关;薄叶山矾(Symplocos anomala Brand)幼苗的存活率与同种幼苗密度、异种大树胸高断面积、林冠开阔度、坡向均呈显著负相关,而与异种幼苗密度和海拔呈显著正相关。本研究表明影响幼苗存活的因子是多样的,而且不是随机发生的。在不同水平上影响幼苗存活的因子不同。

The seedling stage is the most vulnerable stage of life for a plant, and analysis of the factors influencing seedling survival can help us understand species coexistence mechanisms. We examined the importance of biotic and abiotic factors using Generalized Linear Mixed Models with survival data from 3554 seedlings of 128 species in a 25 hm2 Badagongshan forest dynamic plot in central China. Results showed that： （1） At the community level, focal seedling survival was significantly negatively correlated with conspecific neighbor density, indicating negative density-dependence （NDD） effects in this plot, but was positively related to canopy openness. （2） At the age class, the survival of 〈4-year-old seedlings showed significant negative correlation with conspecific neighbor density; for seedlings ≥ 4 years old, the importance of NDD was exceeded by environmental factors. （3）Compared with the evergreen species, the survival rate of deciduous species was more susceptible to conspecific neighbor density, and significantly positively related to canopy openness. （4） The effects of biotic and abiotic factors on seedlings differed among species. For instance, Machilus ichangensis Rehd. et Wils. was positively related to canopy openness, whereas Symplocos anomala Brand seedling survival showed significant negative correlation with conspecific neighbor density, heterospecific adult basal area, and canopy openness, and significant positive correlation with heterospecific seedling neighbor density and elevation.