Anthropogenic climate change has driven shifts in the behavior and life cycles of animals, plants, and numerous other organisms. For plants, numerous studies in temperate habitats have documented the growing season lengthening, causing spring and autumn flowering to occur earlier and later, respectively 1 2 3. These phenological shifts have widespread effects on their ecosystem 4 5 6 7 8. Impacts of these shifts include disruption of species interactions, which in turn fractures communities and food chains 5 6 9 10. Across the tree of life, plant phenology is especially sensitive to a changing climate, with changes in reproductive cycles serving as immediate and visible indicators of change and predictors of more drastic ecological responses 3 7 11 12 13. Because plants are the basis of nearly all terrestrial ecosystems, understanding changes in plant phenology informs our broader understanding of the impacts of climate change.
Global tropical latitudes house approximately 57% of global vascular plant biodiversity 14. Divided into the three regions, the Afrotropics, Neotropics, and Southeast Asia tropics are home to approximately 56,000, 118,000, and 50,000 native vascular plant species14, highlighting the exceptional biodiversity at these latitudes, and particularly the Neotropics, which harbor over half of all tropical species worldwide. In addition, nearly 180 species of plants (and 1,100 species from other groups) from the tropics are described as new to science each year14.
Ecological changes that affect tropical latitudes have cascade effects across the planet15. As a result, documentation of large-scale phenological shifts in and among tropical floras is a crucial piece of information towards full understanding of the global impacts of anthropogenic climate change16. Despite a plethora of studies from temperate latitudes spanning thousands of plant species, we lack comparable and comprehensive information from tropical plants, with all studies to date having been limited to one or a few species17.
Using data from ~ 126,000 museum specimens housed amongst the world’s natural history institutions, we asked whether there have been changes in flowering phenology throughout the global tropics over a 171-year time period. Our analyses spanned some 14 different locations across the planet, exploring changes in both wet and dry habitats in a pairwise framework. We specifically predicted seasonally dry ecosystems would show more pronounced shifts as a result of climate change (compared to wet habitats) under the assumption that dry habitats rely on fluctuations in temperature and precipitation to trigger flowering to a greater degree compared to wet ecosystems. We found that between 1850 to 2021, flowering times shifted significantly at all locations, on average 98 days across sites. Everwett (constantly hot and wet) habitats shifted an average of 95.1 days across 171 years, and seasonally dry habitats shifted an average of 82.5 days across the same time. Our results provide comprehensive evidence for severe climate change across the global tropics and indicate Southeast Asia saw the most drastic shift in flowering date, followed by the Afrotropics, and Neotropics. Additionally, Everwett habitats saw a marginally greater shift in flowering date than seasonally dry habitats.