2.2 Field survey
Twelve 10 m × 10 m study plots were established at 200-m elevational
intervals from 1800 m to 2800 m, extending from the east to the west of
the Yatsugatake Mountains. The plants in each plot were identified based
on the taxonomic groups: trees, shrubs, herbs, ferns, and bryophytes.
Ferns and bryophytes included both epiphytic and terrestrial species.
Epiphytic species were recorded up to 2.0 m from the ground.
To examine the influence of climate on plant diversity, temperature and
relative humidity (RH) were measured in each plot at ~5
cm above the ground at 4-h intervals throughout the year, obtained using
HOBO U23 Pro v2 temperature/relative humidity data loggers (Onset
Computer Corporation, Bourne, MA, USA). To reduce the influence of
sunlight on the measurements, the data loggers were covered by a CO-RS1
solar radiation shield (Onset Computer Corporation). Based on the
measurements of temperature and RH, the following climatic variables
were calculated: mean annual temperature (Tempann), mean
temperature during the growing season (Tempgrow), mean
temperature during the snow season (Tempsnow), mean
annual RH (RHann), mean RH during the growing season
(RHgrow), mean RH during the snow season
(RHsnow), and the duration of the snow season (snow
cover). The series of snow-cover days with over 90% RH was defined as
the snow season. This definition was based on a primary experiment that
buried the data loggers under a snow pack. The remaining days were
defined as the growing season.