Conservation study of Myrsine seguinii in Japan: current distribution explained by past land use and prediction of distribution by land use-planning simulation

The causes of the current distribution of a warm temperate tree Myrsine seguinii population were studied from topographic, geographical, and historical perspectives, and future land management to conserve this species. The study site is the Tokyo University forest located in Chiba Prefecture, at the northern distribution limit of this species. Presence and absence of individuals was surveyed in 10 x 10 m plots along the census line, making a total of 9,697 plots. The current distribution was modeled by multivariate logistic regression using environmental variables determined based on 10-m mesh digital elevation model (elevation, slope, solar radiation, topographic wetness index, surface curvature), 1-km mesh climatic information, and current (2005) and historic (1900) land-use maps. It was clarified that the current distribution area coincides with a Pinus densiflora forest present by the end of the 19th-century Meiji era, where 88.6% of individuals of M. seguinii were found. Inland suitable areas show small patches distributed among the ridges and mountainsides facing south, decreasing as the average monthly minimum winter temperature decreases. Simulated scenarios showed that in the future the potential distribution area of the studied species would decrease in the case of a complete coverage of Cryptomeria or Chamaecyparis plantation, and the case of evergreen broadleaf forest coverage would be better than these plantations. The strong effect of past land use suggests vulnerability and difficulty in the rapid recovery of M. seguinii population from human disturbance.