LAUSR

Abstract Growing degree days (GDD) and chilling requirements (CR) of canopy phenological onset are popular thermal indicators showing forest adaptation to local temperature regimes. This study proposes a satellite-based approach for mapping the canopy-onset thermal traits and analyzing their controlling factors in temperate forests. GDD and CR from 2003 to 2017 were estimated with canopy onset dates and air temperature data retrieved from Moderate Resolution and Imaging Spectroradiometer (MODIS) images. Results revealed that GDD and CR showed distinct geographic patterns with latitude and altitude but with low inter-annual variations of less than 30% of the coefficient of variation. The satellite-based spatial patterns of GDD and CR were well explained by temperature with R-squares of 0.70 and 0.58, which were comparable to 0.63 and 0.59 from the field observation data, respectively. As well, satellite-derived sensitivities of GDD and CR to unit changes in temperature were +52.7 and −21.3°CoC−1, respectively, which were again comparable to the sensitivities from the field data (+50.9 and −29.9°CoC−1, respectively). The patterns and temperature dependency of thermal parameters seem to be relevant to species-level thermal acclimation and community-level plant composition changes with temperature.