麻豆淫院

The annual clock of the seasons鈥攚inter, spring, summer, autumn鈥攊s often taken as a given. But , using a new approach for observing seasonal growth cycles from satellites, shows that this notion is far too simple.

We present an unprecedented and intimate portrait of the seasonal cycles of Earth's land-based ecosystems. This reveals "hotspots" of seasonal asynchrony around the world鈥攔egions where the timing of seasonal cycles can be out of sync between nearby locations.

We then show these differences in timing can have surprising ecological, evolutionary, and even economic consequences.

Watching the seasons from space

The seasons set the rhythm of life. Living things, including humans, adjust the timing of their annual activities to exploit resources and conditions that fluctuate through the year.

The study of this timing, known as "phenology," is . But today, we can also watch phenology from space.

With decades-long archives of satellite imagery, we can use computing to better understand seasonal cycles of plant growth. However, methods for doing this are often based on the of simple seasonal cycles and distinct growing seasons.

This works well in much of Europe, North America and other high-latitude places with strong winters. However, this method can struggle in the tropics and in arid regions. Here, satellite-based estimates of plant growth can vary subtly throughout the year, without clear-cut growing seasons.

Surprising patterns

By applying a new analysis to 20 years of satellite imagery, we made a better map of the timing of plant growth cycles around the globe. Alongside expected patterns, such as delayed spring at higher latitudes and altitudes, we saw more surprising ones too.

One surprising pattern happens across Earth's five Mediterranean climate regions, where winters are mild and wet and summers are hot and dry. These include California, Chile, South Africa, southern Australia, and the Mediterranean itself.

These regions all share a "double peak" seasonal pattern, , because forest growth cycles tend to peak roughly two months later than other ecosystems. They also show stark differences in the timing of plant growth from their neighboring drylands, where summer precipitation is more common.

Spotting hotspots

This complex mix of seasonal activity patterns explains one major finding of our work: the Mediterranean climates and their neighboring drylands are hotspots of out-of-sync seasonal activity. In other words, they are regions where the seasonal cycles of nearby places can have dramatically different timing.

Consider, for example, the between Phoenix, Arizona (which has similar amounts of winter and summer rainfall) and Tucson only 160 km away (where most rainfall comes from the summer monsoon).

Other global hotspots occur mostly in tropical mountains. The intricate patterns of out-of-sync seasons we observe there may relate to , dictating local patterns of seasonal rainfall and cloud. These phenomena are still poorly understood, but may be fundamental to the distribution of species in these .

Seasonality and biodiversity

Identifying global regions where seasonal patterns are out of sync was the original motivation for our work. And our finding that they overlap with many of Earth's 鈥攑laces with large numbers of plant and animal species鈥攎ay not be a coincidence.

In these regions, because seasonal cycles of plant growth can be out of sync between nearby places, the seasonal availability of resources may be out of sync, too. This would affect the seasonal reproductive cycles of many species, and the ecological and evolutionary consequences could be profound.

One such consequence is that populations with out-of-sync reproductive cycles would be less likely to interbreed. As a result, these populations , and perhaps eventually even split into different species.

If this happened to even a small percentage of species at any given time, then over the long haul these regions would produce large amounts of biodiversity.

Back down to Earth

We don't yet know whether this has really been happening. But our work takes the first steps toward finding out.

We show that, for a wide range of plant and animal species, our satellite-based map predicts stark on-ground differences in the timing of plant flowering and in genetic relatedness between nearby populations.

Our map even predicts the complex geography of coffee harvests in Colombia. Here, coffee farms separated by a day's drive over the mountains can have reproductive cycles as out of sync as if they were a hemisphere apart.

Understanding seasonal patterns in space and time isn't just important for evolutionary biology. It is also fundamental to understanding the ecology of , the consequences of climate change for and , and even the geography of agriculture and other forms of human activity.

Want to know more? You can explore our results in more detail with .

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