Aim: Initiation of autumnal leaf senescence is critical for plant overwintering and ecosystem dynamics. Previous studies focused solely on the advanced stages of autumnal leaf senescence and claimed that climatic warming delays senescence, despite the fundamental differences among the stages of senescence. However, the timing of onset of leaf coloration (DLCO), the earliest visual sign of senescence, has been rarely studied. Our aim is to assess the response of DLCO to temperature across the Northern Hemisphere.
Location: 30–75°N in the Northern Hemisphere.
Time period: 2000–2018.
Major taxa studied: Deciduous vegetation.
Methods: We retrieved DLCO from high temporal-resolution satellite data, which was then validated by PhenoCam observations. We then investigated the temporal changes in DLCO and the relationship between DLCO and temperature by using DLCO from satellite data and ground phenological observations. We further estimated the timing of onset of autumnal decline in maximum canopy photosynthetic capacity, an indicator of leaf senescence earlier than DLCO, from FLUXNET CO2 fluxes data, and assessed its response to temperature.
Results: DLCO was not significantly (P < 0.05) delayed between 2000 and 2018 in 94% of the area. DLCO was positively correlated with pre-DLCO mean daily minimum temperature (Tmin) in only 9% of the area, likely because of the overriding photoperiodic control, particularly for woody vegetation, whereas the end of leaf coloration (DLCE) was positively correlated with pre-DLCE mean Tmin over a larger area (34%).
Main conclusions: The coloration progress rate is more sensitive than its start date to temperature, indicating an extension of the duration of leaf senescence under warming. This study indicates that the leaf coloration onset was not responsive to climate warming and provides observational evidence of photoperiod control of autumnal leaf senescence at biome and continental scales.