Science

The arctic tundra’s fall foliage is as vibrant as it is short-lived

Don’t let your eyes deceive you. This isn’t a scene from a crisp fall morning in Vermont or upstate New York—it’s the dry, rocky tundra. Yes, even the mostly treeless tundra can have vibrant fall foliage. But not for long.

In Alaska’s Bering Land Bridge National Preserve, dazzling reds and yellows transform the landscape for just a few short weeks. The preserve is only a little more than 50 miles from Russia, located on part of the land bridge used by humans to journey from Asia to North America during the Pleistocene Epoch around 13,000 years ago. Today, the National Park Service says the preserve helps protect resources used by Indigenous Inupiaq communities who live on the Seward Peninsula.

After the autumn equinox, day length begins decreasing fast in Alaska. In the Northern Hemisphere, as the Earth rotates around the sun, its tilt makes the nights longer and longer between fall and winter. The effects are felt in all 50 states, but nowhere more so than in Alaska. At the Bering preserve, light decreases by about five minutes each day. At its lowest point on the winter solstice, there will only be about 2.5 hours of daylight.

[Related: Climate change is affecting fall foliage, but not in the way you think]

But before temperatures drop well below zero and sunlight dwindles, the shrubs of the preserve’s granite-lined hills have one last thing to do: change colors. Like trees, their leaves take on warmer tones in response to shorter amounts of daylight. In the fall, as light dissipates, leaves stop photosynthesizing like they did in the summer. And in Alaska, light disappears fast, leaving just enough time for brilliant colors to shine through before being covered in a thick blanket of snow and ice. The chlorophyll, which is no longer needed to absorb light, begins to break down in the leaves, leaving behind yellows and oranges underneath. These colors were there all along in the form of carotenes and xanthophyll pigments, but are overwhelmed by the green color reflected by chlorophyll in spring and summer.

As for the reds, cooler weather kickstarts production of a special compound called anthocyanin that plants need to bring nutrients up through their roots. This pigment reflects red light, causing the fiery hues characteristic of fall. 

These processes may be typically associated with the beautiful colors of New England, but it’s the same in the tundra, except instead of gingko, aspens, and maples, the foliage from Alaska willow and dwarf birch shrubs pops. 

[Related: Inside a frozen tunnel hiding the galaxy’s biggest secrets]

Tundras, which comes from a Finnish word meaning “treeless plain,” come in two forms: arctic and alpine. Because biomes vary based on altitude, spots high on mountains across the world share many of the same characteristics as in Bering Land Bridge National Preserve. But the arctic tundra in Alaska is a bit harsher. Plants face a unique set of challenges: the growing season only runs about half as long as the alpine tundra’s, and unlike the alpine tundra, the arctic tundra has poorly drained soil because of the underlying layer of deeply frozen soil called permafrost. This tundra is characterized by low-growing vegetation, including shrubs, sedges, mosses, and grasses with short enough roots so as not to be hurt by the permafrost beneath. Still, approximately 1,700 species of flora call the arctic tundra home.

All tundras are also characterized by their lack of precipitation, with levels on par with the world’s deserts. Seeing as the best conditions for fall foliage involve a wet growing season, that’s a lot to ask of tundras. Lucky for foliage seekers, however, annual summer precipitation has been relatively high over the past decade in Alaska, so now might be the perfect time to see the vivid colors before they disappear in the next month.



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