伏牛山自然保护区森林冠层结构对林下植被特征的影响

在伏牛山自然保护区典型地段设立样方,测定了森林生态系统内几种典型群落类型的冠层结构、光环境特征,调查了林下植被的特征,分析了它们之间的相互关系。结果显示:各群落的冠层结构和光环境有一定的差异,单因素方差分析表明,部分群落间的差异性达到显著水平;各群落灌木层物种丰富度、多样性和均匀度均高于草本层,而优势度正相反;线性拟合的结果表明,草本层的物种丰富度、多样性与冠下光合量子通量密度间呈极显著负相关,优势度与冠下光合量子通量密度间呈显著正相关,灌木层各参数与冠层结构特征间相关性不显著。研究表明,冠层结构的变化对草本层(包括更新幼苗)的影响显著高于灌木层。林隙/林窗或林中空地的出现可能对草本物种或其他阳性及先锋物种具有促进作用,而对优势种幼苗的萌发和定植产生负效应。推测在典型的落叶阔叶林生态系统演替进程中,林下光照强度可能不是最主要的限制因素,优势种种子的扩散、萌发和定植限制可能更重要。

Effects of forest canopy structure on understory vegetation characteristics of Funiu Mountain Nature Reserve

Forest canopy is the most direct and active interface layer between the forest and the outside environment, the canopy structure and the understory light environment have great significance for plant growth and community regeneration. Many previous studies have showed that the emergence of forest gaps and the consequently enhanced light penetration significantly impact the regeneration and colonization of understory vegetation. However, we still have few of knowledge about the relationships between the forest canopy structure and the understory vegetation especially in the ecosystems of the typical mountain deciduous broad-leaved forest (DBF). Therefore, in order to investigate the canopy structure, light environment characteristics, and species diversity of understory communities, as well as explore the relationship between community canopy structure and understory vegetation characteristics in a typical mountain deciduous broad-leaved forest ecosystem, we established sampling plots in representative areas of Funiu Mountain Nature Reserve. We recorded canopy structure, light environment characteristics (using a WinScanopy 2006a from Regent Instruments Inc), and understory plant community (including the shrub layer and the herb layer) characteristics in the plots, and then use a regression analysis (linear curve estimation) to evaluated the relationship between understory vegetation characteristics and canopy structure. The results thus obtained show that: (1) The plant communities certain differed in certain aspects of canopy structure (including canopy openness, gap fraction, leaf area index, and mean leaf angle index) and light environment characteristics (including direct/diffuse/total photosynthetic photon flux density under/over canopy, and extinction coefficient). One-way ANOVA of the raw data indicates that some of the differences between the communities are statistically significant. (2) The species richness, diversity and evenness of the shrub layer were all higher than those of the herb layer, whereas the herb layer has a higher dominance index. As elevation increases, differences in the physical parameters of the two understory layers decreases. (3) We found statistically significant, though weak, negative correlations between herb layer species richness (P=0.006, R²=0.309) and diversity (P=0.008, R²=0.289) and the under canopy photosynthetic photon flux density, as well as a weak positive correlation (P=0.011, R²=0.268) between dominance index of the herb layer and under canopy photosynthetic photon flux density. We did not find any significant correlation between canopy structure and light environment and the parameters of the shrub layer (P>0.05). This study shows that the herb layer (including regeneration seedlings) is more sensitive to changes of canopy structure than the shrub layer (including regeneration saplings). The emergence of forest gaps or spaces may therefore have positive effects on herbaceous plants and other pioneer species, while negatively impacting the germination and growth of dominant species seedlings. This effect may thus produce another succession sequence in the forest gaps, although they may finally develop to the same local climax community type. These above study results make us speculate that, the light intensity in the understory layer may not be the most important limited factor, while the factors about the diffusion, germination and planting of the seedlings of dominant species could be more important in the succession process of the typical deciduous broad-leaved forest ecosystem.