Synchronized Flowering Phenology in Woody Plants Across Three Dimensions: Evidence From Ground‐Based Observations in China During 1981–2020

ABSTRACT Global warming has significantly altered flowering phenology, providing critical insights into how plants respond to climate change. Previous studies have examined broad trends—advances in first flowering date (FFD), regional variation in end of flowering date (EFD) and lengthening of flowering duration (FD)—but research on flowering synchrony remains limited to single sites or a few species, with inconsistent conclusions. Accordingly, we analysed 180 time series for 27 woody plants across 16 sites in eastern China during 1981–2020 to quantify trends in flowering start, end and duration and to test whether synchrony strengthened across spatial (north vs. south), temporal (early‐ vs. late‐flowering) and life‐form (trees vs. shrubs) dimensions by comparing pairwise overlap and gap between pre‐period (1981–1996) and post‐period (2003–2020). The results indicated that flowering synchrony generally strengthened across the three dimensions. Spatially, first flowering date advanced more in the north (−3.3 d decade −1 ) than in the south (−3.0 d decade −1 ). The mean overlap increased by about 2 days from the pre‐period to the post‐period, while north–south differences in both first flowering date and flowering duration diminished by approximately 1 day. Temporally, late‐flowering species advanced more rapidly than early‐flowering species (late‐: FFD −3.7, EFD −3.1; early‐: FFD −2.7, EFD −2.2 d decade −1 ) and differences in first flowering date and end of flowering date each decreased by 3 days. Among non‐overlapping species pairs, 72.9% exhibited shortened gaps. For life forms, shrubs tended to flower earlier and had longer flowering durations than trees, whereas trees showed stronger advances in FFD and EFD (trees: FFD −3.1, EFD −2.7; shrubs: FFD −2.8, EFD −2.1 d decade −1 ) and differences in first flowering date and end of flowering date narrowed by 3–4 days in the post‐period. Among overlapping pairs, 62.8% showed increased overlap. Further analyses indicated that enhanced synchrony was associated with regional disparities in warming rates and interspecific differences in temperature sensitivity. These findings provide a basis for understanding how changes in flowering‐window alignment may affect potential interspecific interactions and forest community reassembly under climate change.