Using Citizen Science to Build Baseline Data on Tropical Tree Phenology

Large-scale and long-term baselines on climate-sensi­tive phenology of widespread tree species are lacking in the Indian subcontinent. Citizen scientists can help bridge this information gap by contributing simple, technology-based data. Here we describe an India-wide initiative called SeasonWatch, with preliminary insights into contributor behaviour and species phenology. Bet­ween 2011 and 2019, cumulative contributor numbers have increased every year, although consistent contribution remains constant and low. We describe seasonal and spatial phenological patterns in most-observed species based on repeated monitoring and one-time ‘bioblitz’ events. We study in detail the flowering phenology of one particular species, Cassia fistula, which appears to show aberrant phenology, reflecting a potential shift away from culturally known flowering dates. We conclude that citizen science-contributed information can be a valuable reference database to compare future changes in tree phenology