Bryophytes play important roles in the ecosystem, such as in water retention and nutrient cycling. Due to the absence of lignified vascular system, they have little ability to regulate internal water content, known as poikilohydry. While some of their traits may be comparable to vascular plants, other traits may show different trends. The objective of this study is to assess bryophyte diversity, their niche preferences and find the relationships among morphological structures and functional traits in relation to light environment and water availability. Bryophytes were recorded in a natural beech forest of Mt. Takanosu, Hiroshima, from various habitats such as tree trunks, rocks, and decayed logs. Among the recorded species, 8 species across different irradiance levels were collected for the measurements of functional traits at cellular level, shoot level, and colony level. Dicranum japonicum and Pogonatum inflexum had the highest chlorophyll concentration among the studied species. This study suggests that in relative irradiance level less than 30%, chlorophyll content increased with irradiance. Meanwhile, chlorophyll a:b ratio also had a positive correlation with irradiance, which is a similar trend seen in vascular plants.