2.1 Study site
The study was conducted in the Yatsugatake Mountains in central Japan. The highest peak of these mountains is the 2899-m summit of Mount Akadake (35°58.259ʹN, 138°22.223ʹE). The vegetation in the Yatsugatake Mountains is classified into the following four types: temperate deciduous forest dominated by Quercus crispula and Larix kaempferi below ~1800 m; subalpine conifer forest dominated by Tsuga diversifolia , Abies veitchii , andAbies mariesii f. hayachinensis at ~1800–2600 m; alpine dwarf pine scrub dominated byP. pumila at ~2600–2800 m; and alpine meadow with turf-rock vegetation at ~2800–2900 m. The subalpine-alpine ecotone at ~2700 m is widely covered byP. pumila . The highest and lowest mean temperatures, obtained from the nearest weather station at 1350 m, are 19.2 °C in August and −5.3 °C in January, respectively, and the mean precipitation is 1439.9 mm/year (Japan Meteorological Agency, 2018).