Trends and Climate‐Sensitivity of Phenology in China's Natural and Planted Forests.

Forest is the largest carbon sink on land, and the timing of forest phenology profoundly influences carbon uptake. However, disparities in the timing and sensitivity of forest phenology, particularly between planted forests (PF) and natural forests (NF), have yet to be determined. In this study, we analyzed the phenological trends and the climate‐sensitivities of China's NF and PF from 2000 to 2022 using field survey data and satellite data. We found that the start of the growing season (start of the season (SOS)) in NF and PF advanced significantly by 0.07 and 0.08 days yr−1, while the end of the growing season (end of the season (EOS)) in both NF and PF delayed by 0.06 days yr−1. Moreover, precipitation and air temperature jointly influenced the timing of phenological events. The pre‐season precipitation delayed the EOS by 0.009 days mm−1 and 0.006 days mm−1 in NF and PF. Moreover, the SOS was more sensitive to precipitation in PF than in NF in arid areas (i.e., pre‐season precipitation <100 mm). Air temperature significantly advanced the SOS by 0.74 and 0.95 days °C−1 in NF and PF and delayed the EOS by 0.89 and 0.71 days °C−1 in NF and PF. Additionally, the sensitivities of SOS and EOS to air temperature significantly differed between NF and PF. Our findings demonstrate a significant phenological discrepancy between PF and NF. The results suggest that NF and PF responded differently to climate variability, implying forest origin should be considered in the projection of carbon sequestration capability under changing climate. Plain Language Summary: Phenology is an important indicator of forest's response to climate change, and its change greatly influences the carbon uptake in forests. In this study, we investigated the phenological changes in China's natural and planted forests, as well as the sensitivity of forest phenology to air temperature and precipitation. We found that the start of the growing season was earlier and the end occurred later in China's forests from 2000 to 2022. Besides, higher air temperature and precipitation could advance the start and delay the end of the growing season in China's forests, respectively. However, the magnitudes of the advancement and delay in phenology to warming and wetting were different between planted and natural forests. We suggest that future studies should consider the impacts of forest origin in biogeochemical simulations. Key Points: The start of the growing season advanced and the end delayed in China's planted and natural forestsThe planted and natural forests differed in their responses to climate variabilityThe start of the growing season was more sensitive to precipitation in planted forests than in natural forests in arid areas [ABSTRACT FROM AUTHOR]