Winter: How plants and animals cope with the cold

When winter sets in, trees stop growing and go dormant to save energy. Water scarcity can become a major problem at this point because if the ground freezes, there's no liquid for the tree roots to drink. And so conifers, which keep their needles year-round, develop a waxy coating in the cold to limit water loss via their leaves.

Deciduous trees, on the other hand, cope by dropping their leaves altogether as winter approaches. They would otherwise lose water from these flatter, broader leaf surfaces through evaporation. Trees can also protect their cells against freezing by moving water from their tissues to spaces outside the cells. Some trees can produce more sugar in winter, increasing their tolerance to the cold.

Harsh winter conditions also add to pressure on animals. Not only is there a drop in the supply of available food, but shorter daylight hours mean there's less time to forage. Many species adapt by stockpiling snacks in advance. This pika — a rodent-like mammal that lives in the mountains of North America, Asia and parts of Eastern Europe — survives by hoarding dried vegetation in its burrow.

Some animals prepare for winter by putting on an extra layer of fat and growing thicker fur. The Arctic fox — found throughout the Arctic tundra biome — even changes color, swapping its darker summer coat for one of pure white. This allows it to hunt prey and blend in with snow and ice on the tundra when the season changes. Its compact body and thick fur on its paws also help retain body heat.

Many mammals, such as marmots, cope with the cold by hibernating — bedding down in a protected burrow or den and entering a deep sleep. In this torpor, they drastically slow their heart rate and breathing, and lower their temperature to save energy. Bears also hibernate, although they develop a thick winter coat and, unlike marmots, keep their body temperature relatively stable during their sleep.

Bears have fur to keep them warm, but what happens to insects when the mercury drops? With bodies made up mainly of water, they need to avoid freezing if they're to survive. Some species manage that just fine by generating an antifreeze that prevents ice crystals from growing in their cells. One study found that the fire-colored beetle could withstand temperatures of -30 degrees Celsius (-22 F).

Mosses in Antarctica have also evolved to withstand subzero temperatures. This flora grows close to the ground to protect it from fierce winds, and can survive without water for long periods when the liquid is locked away in ice. Moss beds sit dormant for months when conditions are too dry, cold or dark, before rapidly reactivating in spring when the ice melts.

Painted turtles overwinter at the bottom of ponds — even in water covered by ice. These North American natives reduce their metabolic rate by over 90%, allowing them to survive without food. Usually they come to the surface for air, but in winter they absorb enough oxygen through their body's surfaces without using their lungs. They can even switch their metabolism to one that doesn't need oxygen.