An innovative international study led by CSIRO, the Australian national science agency, and the University of California, Berkeley, presented a new map of Earth’s seasonal growth cycles. The map reveals global critical points of seasonal asynchrony and demonstrates its surprising ecological, evolutionary, and even economic consequences.
Using 20 years of satellite data and a unique analytical approach, the study, published in Nature, offers the most comprehensive map to date of phenology, or seasonal synchronization, of Earth’s terrestrial ecosystems.
The lead author, Drew Terasaki Hart, an ecologist and data analyst at CSIRO, states that the study identifies seasonal asynchrony hotspots—regions where nearby locations can exhibit drastically different seasonal synchronizations.
“Seasonality is often seen as a simple rhythm — winter, spring, summer, autumn — but our work shows that nature’s calendar is far more complex. This is especially true in regions where the shape and timing of the local typical seasonal cycle differ drastically across the landscape. This can have profound implications for ecology and evolution in these regions,” he explains.
These seasonal asynchrony hotspots are found predominantly in Mediterranean-climate regions and in tropical mountainous regions of Earth. The study provides compelling evidence that seasonal asynchrony in these regions can cause different populations of a species to have incompatible reproductive calendars.
“Our map predicts pronounced geographic differences in flowering calendars and in the genetic relationship between a wide variety of plant and animal species. It even explains the complex geography of coffee harvest times in Colombia — a country where coffee plantations separated by a day’s travel across the mountains can have reproductive cycles as desynchronized as if they were in opposite hemispheres,” he stresses.
Seasonal asynchrony can accelerate evolutionary divergence between these populations and, after a sufficient amount of time, may even lead them to become distinct species — perhaps helping to explain why these regions of great biodiversity also tend to have an exceptional richness of species.
The study also highlights the limitations of more standard satellite-based phenological research approaches. These approaches generally assume simple seasonal cycles, such as those of high-latitude temperate regions.
The use of innovative, biome-independent methods allowed the team to represent subtle and multimodal seasonal growth cycles that can occur in many tropical and arid regions, where previous methods had difficulties.
“Data-driven methods better represent the global diversity of seasonal patterns, which, in turn, allowed us to demonstrate the underestimated value of satellite imagery for understanding global biogeography.”
“We suggest exciting future directions for evolutionary biology, climate-change ecology, and biodiversity research, but this way of viewing the world has even more distant and interesting implications, such as in agricultural sciences or epidemiology,” said Terasaki Hart.
This research was supported by CSIRO, The Nature Conservancy and the University of California, Berkeley, and included data provided by NASA, PhenoCam Network, iNaturalist, and several other sources.
