Population dynamics of Primula sieboldii in the Yatsugatake Forest of Tsukuba University over a 28-year period

Abstract

The Yatsugatake Forest of Tsukuba University contains a large regional population of Primula sieboldii E. Morren, a semi-endangered heterostylous clonal herb. Although P. sieboldii individuals have been observed intermittently in several local populations since 1990, no survey of the entire area has been conducted. Therefore, to clarify the population dynamics of P. sieboldii, we conducted surveys in 2006 and 2018, and compared the results with the 1990 survey records. The total number of P. sieboldii ramets did not change significantly during the 28-year period from 1990 to 2018; however, the number of flowering ramets decreased significantly in recent years, from 2,833 in 2006 to 1,518 in 2018. An even more pronounced decrease was seen in the number of flowering genets, with 939 genets observed in 2006 compared to only 434 in 2018. These decreases resulted in prominent deviations in the morph ratios of local populations, suggesting a likelihood of low seed production and low genetic diversity in future generations.