2020托福听力练习：爬山熊帮助樱桃树种子迁徙（下载）

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　　Picture a brave fireman carrying a pet from a burning building.

　　Now, imagine that global warming is the burning building, a cherry tree is the pet, and a bear is the fireman.

　　You've now got the gist of a new study that finds that cherry trees may be able to survive rising temperatures thanks to mountain-climbing bears that carry the cherry tree seeds to cooler climes.

　　It's projected that, over the next hundred years, temperatures on Earth could rise an average of nearly five degrees Celsius.

　　While some animals might be able to migrate north to escape the brunt of the heat, plants can't uproot themselves quite so easily.

　　But researchers wondered whether the creatures that disperse plant seeds might be able to help.

　　So scientists spent three years sifting through the droppings of Asiatic bears, looking for cherry tree seeds.

　　And they found that the bears were indeed transporting the seeds to cooler locations—not by moving to higher latitudes, but higher altitudes.

　　Seems the bears snack on the fruits that are found at the foot of the mountains in spring and then make the climb to higher elevations to enjoy young leaves and buds and flowers, particularly as the season progresses.

　　The researchers could tell that seeds had been deposited higher up the mountain than they had been harvested by the ratio of their oxygen isotopes, which changes with altitude.

　　And the 300 or so meters the seeds ascended should buy the resulting trees a degree or two in heat relief.

　　The study is in the journal Current Biology.

　　The finding is good news for plants, like cherry trees, that fruit in spring.

　　Unfortunately, the results suggest that plants that fruit in fall, when bears are headed back down for hibernation, will have to hold out for a different animal hero.

　　Or for a bear with a bad sense of direction.