This study was conducted at the Kraichtal, southern Germany. Through the measurements of the relative illuminance under canopy and the coverage of many undergrowing species in 13 plots of forest communities, the correlation between the relative illuminance and the coverage of the species was calculated. The adaptation of 12 undergrowing species to light condition was determined based on the above calculation. Combining the indicator values of the species to ecological factors like light, humidity, temperature, acidity and nitrogen content in the soil with the constancy values of species in communities, the ranking order of undergrowing species in the communities was also examined. The results show: 1) In determining the light distribution in a forest community, scattered light condition is preferable because the interference from the drifting of light spots under the tree canopy can be reduced, and thus relatively stable distribution of light radiation can be obtained. 2) The distribution of 9 species, out of 12 species studied, was linearly correlated with the light condition under the canopy. For 7 of the 9 species, the correlation between the coverage of species and the relative illuminance was positive, and negative for 2 of them. For the other 3 species under the canopy the coverage was not correlated with the relative illuminance. 3) Compared with the light indicator values of species, the quantitative analysis of the relationships between species coverage and relative illuminance is more effective to reflect the adaptation of the species to light conditions under canopy and to reveal the ecological range of illuminance level of the species. 4) The relative adaptability of different species to light conditions directly affects the inter-specific relationships of the undergrowing species and may determine their ranking order in a community. The species with euphotic ecological range of illuminance level were easier to adapt to different light conditions under tree canopy and thus were able to exist in most forest community types with high constancy values.
江源1 Manfred MEURER2
（1. 北京师范大学资源科学研究所，教育部环境演变与自然灾害重点实验室，北京100875；2.Institute of Geography and Geoecology, University of Karlsruhe,Karlsruhe 76128,Germany)
摘要：通过在 13个样地中测定林下相对照度和多个植物物种的盖度指标 ,建立了林下相对照度与林下植物盖度变化的相关关系 ,对德国南部落叶阔叶林下 12种植物的光适应性进行了分析。结合植物的生态因子指示值和种在群落中的恒有度等生态指标 ,探讨了林下植物群落地位的形成原因。结果表明 :1)在散射光条件下进行森林群落中的光照分布特征测定 ,能够降低光斑造成的干扰 ,获得相对稳定的光分布 ;2 )在被研究的 12个物种中 ,有 9种植物在林下的分布与光照条件相关显著 ,其中 7种植物的盖度与相对照度之间具有正相关关系 ,2种植物具有负相关关系。其余 3种植物的盖度与相对照度之间无显著的线性相关 ;3)与光指示值相比 ,盖度与照度之间关系的定量分析能够更清楚地反映林下植物的光适应性 ,揭示植物的光生态幅特征 ;4)光适应性直接影响着林下植物的种间关系 ,也影响着物种的群落地位和作用。光生态幅广的植物 ,在群落中具有较强的适应能力 ,因此能够在多种群落类型中出现 ,表现出较高的恒有度值。