Tropical flowers are blooming months earlier or later than they used to because of climate breakdown, with potentially “cascading impacts across ecosystems”, according to a study of 8,000 plants dating back 200 years.
Researchers looked at flowers from a range of countries, including Brazil, Ecuador, Ghana and Thailand, home to the most biodiverse ecosystems on Earth, but also the most understudied.
The Brazilian amaranth tree flowers 80 days later than it did in the 1950s, while the Ghanaian rattlepod shrub’s flowering period shifted 17 days earlier between the 50s and 90s, according to a study of museum specimens.
It was previously thought that tropical regions – where temperatures fluctuate less over the course of the year – would not be so affected by the climate crisis in terms of the timing of flowering. This hypothesis has been proved wrong, said the lead researcher Skylar Graves from the University of Colorado Boulder, who added that “nowhere on Earth is unaffected by climate change”.
“This is a major problem, because not only do the tropics make up a third of the globe, but they are the most biodiverse ecosystems on Earth,” said Graves. Nearly 180 species of plants new to science are found in the tropics each year, according to the paper.
Museum specimens were used to compare historic and current flowering times. Pictured: Peltogyne recifensis (left) and Aeschynomene indica. Photograph: Courtesy of Skylar Graves
Researchers compiled museum data of 33 tropical species from between 1794 and 2024. The timings of flowering had shifted by an average of two days a decade, according to Graves, who spent years going through dried flower collections.
The entire tropical ecosystem is likely to be negatively affected. “These changes, and more in turn, fracture communities and food chains,” the researchers wrote in the paper published in the journal Plos One, describing the changes as potentially causing “cascading impacts across entire ecosystems”. The tropics is a “large blind spot regarding understanding the global impacts of climate change”, they wrote.
It is likely that these changes have wider impacts on the ecosystem as flowering falls out of sync with the cycles of fruit-eating, seed-dispersing animals (meaning there is not fruit available for them to eat when they are expecting it) as well as other plants and pollinators.
If, for example, a flower needs to be pollinated by a migratory bird but that bird is only around for a few days a year and the timing no longer lines up, the flower won’t get pollinated and the bird won’t get the nectar to drink.
“Ecosystems are very delicate webs of interactions, and if there is one element out of sync, especially with the plants, which are the basis of the ecosystem, things can fall apart at every level of the ecosystem,” said Graves. Many animals that rely on these plants are primates, which are already considered at risk.
The study showed impacts similar to changes documented in temperate, boreal and alpine desert plants. Different species rely on different cues to trigger flowering – for some it could be the warmest temperature during the day, for others the coolest temperature at night. “If climate change strengthens or brings forward a flowering cue, a species may flower earlier. If it disrupts or delays that cue, flowering can be pushed later. That’s why we see both advances and delays, even within the same region,” said Graves.
Tropical ecosystems are components of wider planetary health, and changes in these regions can have cascading impacts around the globe. “The tropics are at just as much risk as the temperate location you call home, and because of that, just as much effort is needed in the conservation of these ecosystems,” said Graves.
Dr Emma Bush from Royal Botanic Garden Edinburgh, who was not involved in the research, said: “The complex seasonality of tropical ecosystems has been understudied and misunderstood for far too long … This highlights how much more work is needed to document and understand tropical ecosystems and the impact climate change is having on them.”
She added: “This study adds to the mounting evidence that the different elements of ecosystems may be responding to a changing climate at different rates. When plants, insects and other animals are out of sync they could all lose out – and the risk is that we lose biodiversity that benefits people, too.”
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