Temporal Flowering Patterns of Seventeen Mangrove Species in the Indian Sundarbans: A Field-Based Phenological Assessment

Mangrove flowering phenology is a crucial bio-indicator for assessing ecosystem health and developing strategies against climate change. However, comprehensive field studies are scarce in the Indian Sundarbans. We conducted 19 months of observations (January 2015–July 2016) across 78 transects covering a total area of 128 km² to document flowering patterns of 17 mangrove species. Using a standardized flowering index (SFI), we quantified temporal variations in reproductive activity across nine plant families. We observed three distinct flowering seasons: spring peak (March–May), dominated by Aegiceras corniculatum (SFI = 2.78), Sonneratia caseolaris (SFI = 2.97), and Avicennia species; monsoon flowering (June–July) primarily featuring Avicennia species; and post-monsoon flowering (September–October) characterized by Rhizophora apiculata (SFI = 3.25) and associated species. Hierarchical clustering revealed four phenological groups where genus-level conservation of Avicennia species was evident. Convergent flowering strategies across taxonomically diverse taxa was also observed. The bimodal flowering pattern may serve as essential year-round resource for pollinators. These baseline data provide essential reference points for mangrove conservation planning and climate change adaptation strategies in this globally significant ecosystem.