We evaluated the spatial characteristics of the first day of peak leaf colouring ( PLC start ) 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 PLC start dates (day of year 265–294) displayed steeper slopes in elevation per degree of latitude than locations with later PLC start dates (day of year 295–314). This statistically significant result indicates that the influence of elevation on PLC start (vertical gradient) weakened as the leaf colouring season progressed in Japan. In addition to these spatial characteristics, the PLC start 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 PLC start 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.

中文翻译：

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使用在线物候数据评估日本沿纬度和海拔梯度的秋季叶色峰值

我们评估了 2015 年至 2017 年日本叶片着色峰值 (PLC start) 第一天的空间特征及其与气温沿纬度和海拔梯度的关系。分析了通过公民科学从 740 多个站点收集的叶片着色信息，代表从 0 到 2800 m 的海拔和从 32°N 到 44°N 的纬度。我们发现，与 PLC 开始日期较晚（年份 265-294 日）的位置相比，PLC 开始日期较晚（年份 265-294 日）的位置每纬度显示出更陡峭的海拔斜率。这一具有统计学意义的结果表明，随着日本叶子着色季节的进展，海拔对 PLC 开始（垂直梯度）的影响减弱。除了这些空间特征，PLC 开始和温暖指数（基于月平均气温）显示出纬度和海拔梯度的显着线性相关性。这一结果表明，PLC 开始对气温的敏感性，如纬度和海拔梯度所示，是恒定的。这项研究表明，在线物候数据可能比以前研究使用的数据集提供更准确的区域尺度（100-1000 公里）结果。