Treeline Shift During the Last 40 Years on the West-Facing Slope of Mt. Rishiri

Abstract

We analyzed the vegetation change during the last 40 years near the treeline in order to examine its upward shift on Mt. Rishiri, northern Japan. The land-cover classifications derived from past aerial photographs indicated an increase in the forest area and its expansion to higher altitude on the west-facing slope of Mt. Rishiri. The logistic regression model showed that the treeline has moved 41.9 m upward during the last 40 years, and the mean rate of treeline advance was 1.0 m year^–1. The temporal comparison between aerial photographs taken in 1977 and processed unmanned aerial vehicle (UAV) images taken in 2019 demonstrated that the density of Betula. ermanii canopy trees significantly increased near the treeline. Moreover, some of the novel forest stands consisting mainly of B. ermanii were observed in the Pinus pumila community and sasa grassland above the treeline. These results provide direct evidence of the upward treeline shift during the last 40 years on the west-facing slope of Mt. Rishiri, but also indicate that the upward treeline shift was caused by the regeneration of Betula forests in the alpine zone.