Flowering and fruiting of a dwarf bamboo, Sasa borealis for 33 years in Ogawa research site in northern Ibaraki prefecture, Japan.

Abstract

The dwarf bamboo species have been considered to repeat flowering and seedling regeneration at long intervals ranging from several decades to 120 years. However, the flowering of dwarf bamboo species varies from large-scale mass flowering of several hundred hectares to small-scale sporadic flowering of a few square meters, depending on the species, region and year. The objectives of this study are 1) to document the flowering phenomena in Sasa borealis communities, 2) to clarify the difference in sound seed rate between mass and sporadic flowerings, and 3) to examine the dormancy and germination of Sasa borealis seeds. In the Ogawa Forest Reserve, we could observe various types of flowering of Sasa borealis at six locations over a 33-year period (1990–2023). These were three small mass flowerings of 0.45 ha or more area in 2017, and three sporadic flowerings of a few square meters in 1991, 2020, and 2023. During small-scale mass flowering, inflorescence of different sizes emerged from buds of culms and rhizomes, but sound seeds occurred only on inflorescence branched off from culms. The sound seed rate was 7.9–10.2% in the one mass flowering patch, but no sound seeds were observed in the low-density patches in mass flowering. On the other hand, sound seed was not found in all of three sporadic flowerings. Mass flowering produced 1176 ± 945 seeds/m² in 2017, and an average of 0.63 seedlings/m² were present in 2018 and 2.46 seedlings/m² in 2020. These results indicate that Sasa borealis can produce seeds even in small-scale mass flowering of about 0.45 ha, and that the seeds are dormant and likely to germinate within two years after fruiting. Future research will focus on the competition and survival between Sasa borealis, tree seedlings and other dwarf bamboos at the site after the simultaneous flowering and death of the former.