Peak autumn leaf colouring along latitudinal and elevational gradients in Japan evaluated with online phenological data
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ORIGINAL PAPER
Peak autumn leaf colouring along latitudinal and elevational gradients in Japan evaluated with online phenological data Shin Nagai 1
&
Taku M. Saitoh 2 & Tomoaki Miura 3
Received: 6 July 2019 / Revised: 17 March 2020 / Accepted: 20 April 2020 # ISB 2020
Abstract We evaluated the spatial characteristics of the first day of peak leaf colouring (PLCstart) and their relationships with air temperature along latitudinal and elevational gradients in Japan from 2015 to 2017. Leaf colouring information collected from more than 740 sites via citizen science was analysed, representing elevations from 0 to 2800 m and latitudes from 32°N to 44°N. We found that locations with earlier PLCstart dates (day of year 265–294) displayed steeper slopes in elevation per degree of latitude than locations with later PLCstart dates (day of year 295–314). This statistically significant result indicates that the influence of elevation on PLCstart (vertical gradient) weakened as the leaf colouring season progressed in Japan. In addition to these spatial characteristics, the PLCstart and the warmth index (based on monthly mean air temperature) showed significant linear correlations for latitudinal and elevational gradients. This result suggests that the sensitivity of PLCstart to air temperature, as manifested in both latitudinal and elevational gradients, is constant. This study suggests that online phenological data may provide more accurate results for a regional scale (100–1000 km) than the datasets used by previous studies. Keywords Japan . Latitudinal gradient . Elevational gradient . Leaf colouring . Website
Introduction Autumn phenology (leaf colouring) is not as well understood as spring phenology (flowering and leaf flush) (Gallinat et al. 2015; Xie et al. 2018). Quantitative knowledge of the spatial Re-submitted to International Journal of Biometeorology * Shin Nagai [email protected] Taku M. Saitoh [email protected] Tomoaki Miura [email protected] 1
Earth Surface System Research Center, Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama 236-0001, Japan
2
River Basin Research Center, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan
3
Department of Natural Resources and Environmental Management, University of Hawai’i at Mānoa, 1910 East-West Road, Honolulu, HI 96822, USA
and temporal variability of leaf colouring, a proxy for the end of the annual cycle of terrestrial photosynthesis, is needed for a fuller understanding of the interaction between the atmosphere and vegetation under climate change (Xie et al. 2018). Leaf colouring also provides a cultural ecosystem service through tourism (Rozenstein and Adamowski 2017). Leaf colouring shows spatio-temporal variations along latitudinal (horizontal) and elevational (vertical) gradients (Doi and Takahashi 2008; Gill et al. 2015; Nagai et al. 2015a; Park et al. 2017). For instance, one simple approach to evaluate the geographic distribution of leaf colouring is Hopk
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