How did the characteristics of the growing season change during the past 100 years at a steep river basin in Japan?

Abstract

The effects of climate change on plant phenological events such as flowering, leaf flush, and leaf fall may be greater in steep river basins than at the horizontal scale of countries and continents. This possibility is due to the effect of temperature on plant phenology and the difference between vertical and horizontal gradients in temperature sensitivities. We calculated the dates of the start (SGS) and end of the growing season (EGS) in a steep river basin located in a mountainous region of central Japan over a century timescale by using a degree-day phenological model based on long-term, continuous, in situ observations. We assessed the generality and representativeness of the modelled SGS and EGS dates by using phenological events, live camera images taken at multiple points in the basin, and satellite observations made at a fine spatial resolution. The sensitivity of the modelled SGS and EGS dates to elevation changed from 3.29 days (100 m)−1 (−5.48 days °C−1) and −2.89 days (100 m)−1 (4.81 days °C−1), respectively, in 1900 to 2.85 days (100 m)−1 (−4.75 days °C−1) and −2.84 day (100 m)−1 (4.73 day °C−1) in 2019. The long-term trend of the sensitivity of the modelled SGS date to elevation was −0.0037 day year−1 per 100 m, but the analogous trend in the case of the modelled EGS date was not significant. Despite the need for further studies to improve the generality and representativeness of the model, the development of degree-day phenology models in multiple, steep river basins will deepen our ecological understanding of the sensitivity of plant phenology to climate change.

Review: Monitoring of land cover changes and plant phenology by remote‐sensing in East Asia

“…In addition, the development of statistical phenology models may bridge the gap between the periods covered by in situ and satellite observations because the models can estimate the spatial and temporal variability of such phenological events since long before the history of satellite observations. Shin et al (2021) validated the relationship between the timing of leaf‐flushing and leaf‐fall in a deciduous broadleaved forest in Japan, with the dates estimated by a statistical phenology model based on in situ observation data and GRVI values calculated from Sentinel‐2A/2B satellite data.…”

“…In previous studies (Table 1), researchers used satellite data for phenological observations. Using such data, the geographic distributions of the leaf‐flushing and leaf‐fall dates along elevational and latitudinal gradients were detected in China (Cong et al, 2013; Piao et al, 2011; Wu et al, 2016) and Japan (Nagai et al, 2015; Nagai, Nasahara, Akitsu, et al, 2020; Shin et al, 2021). The long‐term trends and the amplitude of year‐to‐year variations in leaf‐flushing and leaf‐fall dates were detected at a decadal scale on the Tibetan Plateau (Piao et al, 2011) and in Europe (Garonna et al, 2014), the northern hemisphere (Piao et al, 2007), and the world (Buitenwerf et al, 2015; Zhang et al, 2014).…”

Perspective: Improving the accuracy of plant phenology observations and land-cover and land-use detection by optical satellite remote-sensing in the Asian tropics

“…Despite the uncertainty caused by the heterogeneity of tree species and microtopography, previous studies indicated that the time-series of vegetation indices could be used to accurately detect the spatiotemporal variation of leaf flush and leaf fall in deciduous forests in Japan by validating the indices against longterm continuous in situ observed data (Miura et al, 2019;Yan et al, 2019). Despite the effect of microtopography (elevation) on phenology and the differences in timing and patterns of leaf flush and leaf fall among tree species (Inoue et al, 2014;Nagai et al, 2014b;Shin et al, 2021a), leaf flush and leaf fall within a narrow region (e.g., 1,000-m square) occur rapidly and nearly simultaneously. The Japanese government is planning to launch a geostationary satellite with an optical sensor with a 3-to 4-m spatial resolution.…”

Interannual Variation and Trend of Carbon Budget Observed Over a 28-year Period at Takayama in a Cool-Temperate Deciduous Forest in Central Japan

“…Similarly, the first day of the year that LAI fell below 50% of the average value of the LAI over DOY 180-240 of the year was defined as an indicator (LFLAI) of the occurrence of LF. Furthermore, we also calculated the occurrences of LE and LF of canopy trees of each year using a degree-day model of vegetation phenology by Nagai et al (2021). In the model optimized to reproduce the phonology events at TKY, the LE date (LECET)…”