To survive rapidly warming climates, temperature-sensitive plants must adapt to the heat or risk extinction.
But there is another option is on the table — they can move.
Higher latitudes offer more tolerable temperatures, but for some plants, including wild cherry trees, a change in altitude might do the trick. After all, temperatures drop rapidly (-0.65 degrees Celsius per 100 metres of altitude) as you move up a mountain. This means moving a relatively short distance vertically can be a useful way for plants to escape the heat.
Researchers reporting in the journal Current Biology have now shown that cherry trees are indeed making their way to the mountaintops — but not without a little help from cherry-loving, mountain-climbing bears.
From 2010 to 2013, the researchers in Japan tracked the movement of wild cherry seeds in the dung of Asiatic black bears and small mammals known as Japanese martens. The bears were involved in most of the seed movements.
By measuring the ratio of stable oxygen isotopes in the seeds, which gives a reliable estimate of the temperature the plant was exposed to when it grew, the researchers could pinpoint their locations of origin. The authors concluded that bears disperse the cherry seeds over several hundred meters vertically, and almost always toward the mountaintops.
"We show that bears disperse seeds toward mountaintops, probably because bears climb mountains following the spring plant phenology, proceeding from the foot to the top of mountains," first author Shoji Naoe of the Forestry and Forest Products Research Institute in Japan said in a press release.
The bears were found to move the seeds to locations that are about 1.0 or 2.0 degrees Celsius cooler, which the researchers deemed to be sufficient to offset the estimated global temperature rise of almost 5 degrees Celsius by the year 2100.
While dispersal by bears appears to be protecting these cherry trees from the effects of global warming, not all plants will be so fortunate. In particular, plants that fruit later in the year tend to be dispersed by mammals on their way move down from the mountains.
"Seed dispersal toward the base of the mountain is a tragedy under global warming," Naoe said.
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