In many parts of the world, people might dust off their heavy coats at the first sight of winter or switch to a light t-shirt and shorts after spring gives way to summer. The timing is often taken as a given, but a recent study led by Drew Terasaki Hart, PhD ’22 Environmental Science, Policy, and Management (ESPM) suggests that the changing of the seasons is far more complex than some people realize.
A new analysis of two decades' worth of satellite imagery provides an unprecedented and intimate portrait of the seasonal cycles of Earth’s land-based ecosystems. The study, which was published in a September 2025 issue of Nature and featured on its cover, identifies global hotspots where the timing of seasonal cycles can be out of sync between nearby locations. These differences in timing can have surprising ecological, evolutionary, and even economic consequences.
“Understanding seasonal patterns in space and time isn’t just important for evolutionary biology,” explained Terasaki Hart, who conducted the study as part of his dissertation in the lab of ESPM professor Ian Wang and now works as an ecologist and data analyst for the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia’s national science agency. “It is also fundamental to understanding the ecology of animal movement, the consequences of climate change for species and ecosystems, and even the geography of agriculture and other forms of human activity.”
According to their analysis, the authors found that spring has a delayed onset in locations at higher altitudes and higher equatorial latitudes, as expected. But they also found that Mediterranean climates worldwide—characterized by mild, wet winters and hot, dry summers—experience a “double peak” pattern of photosynthesis rates. This pattern has been previously observed in California, where photosynthesis rates in grasslands and chaparral ecosystems peak in April and rates in evergreen forests peak in June. Through their analysis, the researchers observed similar effects in Chile, South Africa, southern Australia, and the Mediterranean.
Regions where seasonal activity and climate patterns are out of sync between nearby locations were found to overlap with biodiversity hotspots. The authors note that these differences in seasonal timing can potentially influence the reproductive cycles of many animal species and alter the harvest patterns of agricultural crops.
The study was co-authored by Wang and UC Berkeley alumni Thảo-Nguyên Bùi, BS ’21 Environmental Sciences and Environmental Economics and Policy, and Lauren Di Maggio, BA ’21 MA ’23 Statistics. Bùi was involved in the project through Rausser College’s Sponsored Projects for Undergraduate Research, while Di Maggio joined through UC Berkeley’s Undergraduate Research Apprentice Program. They helped Terasaki Hart and Wang gather and prepare the data, develop the analyses and figures, and write the manuscript.
Read more about the study in Nature, and explore its results in more detail using this interactive online map. You can also watch an animation of the seasonal cycles of plant growth around the world, created by researchers.
