Knotweed in Japan:

Reynoutria japonica is a common perennial pioneer species on Japanese volcanoes. In a volcanic desert (1500 m above sea level) on Mount Fuji (3776 m), central Japan, this species forms circular stands (patches). As a patch develops, shoot density decreases in its centre (‘central die-back’). The central die-back has been considered a key process in the early stages of primary succession, though its mechanism has been unknown. ... Two of the species colonizing die-back areas are Aster ageratoides and Miscanthus oligostachyus.

Central Die-back of Monoclonal Stands of Reynoutria japonica in an Early Stage of Primary Succession on Mount Fuji. Annals of Botany 77, 477–486, 1996

PLB

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