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This phenomenon, known as seasonal asynchrony, occurs in specific locations such as the tropical mountains of Costa Rica and California, which has a Mediterranean climate. In these places, plants bloom at different times, disrupting the usual seasonal patterns.
The study used satellite images to identify regions where short distances separated locations that appeared to be in two different seasons. Researchers found that certain environments experience the peak “greenness” of spring roughly two months earlier than forest ecosystems, leading to a “double peak.”
While researchers identified several areas with this pattern—such as Chile, South Africa, southern Australia, California, and the Mediterranean—they don’t yet have a unifying explanation for why it happens.
“In places like California, there’s a complex ‘dance’ of rhythms across the landscape,” said study author Drew Terasaki Hart. “In the tropics, we know much less.”
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To track plant growth from space, researchers analyzed 20 years of satellite images and estimated vegetation by calculating how much infrared light bounced off Earth’s surface. This approach revealed differences in seasonal rhythms between any two places, producing a map showing these variations globally.
Hart and his co-authors found that seasons peak at different times across certain regions, including five with similar climates: Chile, South Africa, southern Australia, California, and the Mediterranean. The main pattern was particularly evident in tropical mountains but surprised researchers when it appeared in Mediterranean regions.
The primary drivers of this phenomenon are likely differences in temperature and precipitation. For example, trees in California’s valleys soak up winter water and start growing early, while mountain trees with deeper roots grow once temperatures warm up. In the tropics, tall trees can extract water from clouds, making plant growth closely related to light and water availability.
Researchers believe that out-of-sync seasons could lead to the creation of new species by causing neighboring animal groups to breed at different times. However, more research is needed to confirm this hypothesis.
Hart hopes his findings will help explain why tropical mountain regions have such high biodiversity. The study provides a unique worldwide look at variations in seasonal activities like plant growth and opens up many possibilities for future research.
