Culm dynamics of dwarf bamboo ( Sasa kurilensis Makino & Shibata) in relation to forest canopy conditions in beech forests

The dynamics of understorey dwarf bamboos are an important factor in forest dynamics. Although there have been a number of recent reports about the regeneration process after the simultaneous flowering and death of bamboos, the long-term dynamics of dwarf bamboos on the forest floor and outside the regeneration process (i.e., nonflowering state) are unclear. The present study aimed to investigate the long-term changes in Sasa kurilensis Makino & Shibata (Poaceae, Bambusoidae) populations in relation to the forest canopy and environmental conditions in the primeval beech forests of Shirakami-Sanchi World Heritage Area, Japan. Ten permanent plots (2 x 5 m) were established at three study sites (1 ha) in beech forests. Each site differed in forest structure. All S. kurilensis culms were censused from 2001 to 2019. The estimated maximum longevity of culms indicated that S. kurilensis culms can survive up to approximately 7000 days, nearly 20 years. The culm density and above-ground biomass varied widely amongst the study plots, and abrupt changes were observed in some plots affected by changes in the forest canopy conditions, such as gap formation. The relationship between canopy closure and culm density in 2001 showed an inverse proportional trend that weakened in 2019, indicating that S. kurilensis developed its population under closed canopies (dark conditions). More attention should be paid to such wide variations and unstable changes in understorey bamboo populations if the dynamics of these forests are to be better understood.