Climate‐Driven Shifts in Flowering Phenology of Wild Tropical Plants Uncovered by Century‐Long Herbarium and Photographic Records

Research on phenological responses to climate change has primarily focused on temperate regions, while tropical species remain critically understudied due to a historical scarcity of long-term monitoring data in these areas. We utilized digitized herbarium specimens and photographs to analyze century-long shifts (1921-2020) in the flowering phenology of 56 native plant species on Hainan Island, China. Species-specific linear models were used to quantify phenological responses of flowering day of year (DOY) to temperature and precipitation, and linear mixed-effects models were applied to test whether these responses differed among flowering seasons. We further evaluated phylogenetic signals in flowering date and climatic sensitivities and used phylogenetic generalized least-squares models to compare functional groups while accounting for phylogenetic non-independence. Our results revealed strong seasonally divergent responses to warming: increasing temperatures significantly delayed flowering of spring- and summer-flowering species (+5.01 ± 0.32 and + 1.96 ± 0.47 days/°C, respectively), whereas they advanced flowering of autumn-winter-flowering species (-5.61 ± 0.64 days/°C). Increased precipitation was associated with delayed flowering in spring and summer (+3.54 ± 0.21 and + 4.21 ± 0.17 days/10 mm, respectively). We detected no significant phylogenetic signal in flowering date or climatic sensitivities. Flowering season was significantly associated with both temperature and precipitation sensitivities, whereas most functional-group differences within flowering seasons were nonsignificant. Our findings reveal strong seasonal heterogeneity in tropical flowering responses to climate and highlight the need to incorporate such heterogeneity into projections of tropical plant responses to future climate change.