A species of bamboo found all over Japan – Phyllostachys nigra var. henonis – is about to flower for the first time in 120 years, and then die.
The flowering event, expected in 2028, could have wide ramifications for the country’s ecology and economy.
But researchers don’t know exactly how the plant regenerates – or what’s going to happen in 5 years’ time.
Phyllostachys nigra var. henonis, sometimes called henon bamboo, is native to China, but has been cultivated in Japan since the 9th century.
It’s one of the most common varieties of bamboo in Japan, which has around 1700km2 of bamboo forests.
All bamboo is “monocarpic”: it flowers once, then dies. Some bamboo species live for a couple of years before their flowering, but many live for decades. Phyllostachys nigra var. henonis has an unusually long flowering interval of 120 years: the last major flowering of henonis was in 1908.
Because it happened so long ago, scientists don’t know how the plant regenerates.
Researchers at Hiroshima University found a stand of henon bamboo flowering early, in 2020. They used this opportunity to set up a plot and observe the bamboo as it germinated.
They’ve published their findings in PLOS One – but they’ve not managed to solve the mystery yet. While the plants did produce seeds, none of them grew into new bamboo plants.
“The bamboo did not produce any viable seeds that can germinate. Bamboo shoot production was stopped after flowering. There was no sign of regeneration of this bamboo after flowering for the initial three years,” says first author Toshihiro Yamada.
This implies the bamboo is hard to regenerate – but, as the researchers say in their paper, “this idea is clearly contradicted by the fact that this species has survived for more than 1,000 years in Japan after its introduction from China”.
“Phyllostachys nigra var. henonis must have regenerated repeatedly, as it surely has experienced many flowering events during this period.”
The researchers propose several suggestions for how the bamboo regenerates, such as underground organs that let the plant regrow.
But in the meantime, this means that henon bamboo will be slow to grow back, when it dies in 2028.
“So, a bamboo stand will turn into a grassland after flowering, for at least several years. We may need to manage this drastic change after bamboo flowering,” says Yamada.
“During the initial regeneration process, which will last at least several years, bamboo stands will obviously be useless as sources of craft materials and edible bamboo shoots,” write the researchers in their paper.
“Because P. nigra var. henonis plays an important role in human society in Japan, the dieback of entire stands after flowering will result in huge economic losses.”
The researchers also voice concerns for the environmental implications of this dieback, which could cause “drastic” changes in vegetation and land cover, big biomass loss, and soil erosion.
They state in their paper that there might be artificial ways to prevent this, including fertiliser and planting new stands. They also point out that the bamboo dieback could be an opportunity: henon bamboo grows very vigorously, invading forests and farms.
“Once these new stands are established, great effort is required to prevent further spread. Furthermore, the removal of bamboo stands is time- and labour-consuming owing to their dense underground systems,” write the researchers.
“If land needs to be cleared of bamboo in preparation for other uses, the period after flowering, when bamboos are weak, is clearly the best time.”
