Life Beneath the Snow and Ice
Winter in southwest Colorado is finally here! In this weather our local animals have many survival strategies – they may migrate, hibernate, or adapt their lives to the new surroundings. However, some of the most fascinating animals are those that manage to survive while remaining underneath large amounts of snow throughout the winter. Their environment is called the subnivian zone, meaning “under snow”.
When the temperatures get frigid outside, a deep layer of snow – about 10 inches or so – can act as an insulating layer to animals beneath it. The warmth here actually comes from the Earth’s core. The snow at the bottom of this layer changes form, and becomes ‘sugar snow’, or depth hoar, where the flakes don’t stick together very well. This is a benefit to small animals who can then move through it easily. Some of the most common animals that can be found under the snow are mice, voles and shrews. They burrow under the snow, finding seeds, stems and even beetles and larvae to eat. Some of the plants they find to eat even manage to stay green and growing during the winter. The small mammals living here make an amazing network of snow tunnels, and even create air shafts to get oxygen. However, it is typically very dark under the snow, making eyesight a secondary sense to these animals. Whiskers help profusely to help them find their way through the network of tunnels.
Despite these small mammals seeming to be well hidden under the snow, predators such as ermine, owls, foxes and coyotes are aware of their presence. Ermine, or long-tailed weasels, are small and thin enough to actually enter the tunnels, while larger predators appear from above, diving snout first (such as with coyotes and foxes) or feet first (such as with owls and other raptors) to grasp their prey. When you’re out this winter, look for the beautiful wing prints that owls and other raptors leave in the snow when capturing their prey.
Animals even smaller than mice manage to live under the snow as well. This includes mites, springtails and spiders. Springtails, which are small insects that can spring themselves into the air can actually be seen above the snow as well on warmer winter days, and are a great food source for the spiders under the snow. In order to survive under the snow some spiders and insects produce a sort of antifreeze in their bodies which prevents ice crystals from forming.
Things also change for animals and plants beneath the ice in the winter. Water beneath the ice doesn’t freeze, but it still remains extremely cold – usually in the mid-‘30s. Actually, the main problem for animals down there is not the cold, but the lack of oxygen in the water. During the rest of the year oxygen is added to the water through air and water currents, waves, and plants photosynthesizing. In the winter, none of this happens. Animals that live beneath the ice are cold blooded, meaning their body temperature is the same as their environment. Thus their metabolism slows down, as do their movements – some even become dormant. In this way they need less oxygen and food through the winter.
When outside this winter, you can experiment with your own ‘subnivean zone’ by creating a snow shelter, sometimes called a quinzee. These need to have quite thick walls (1 – 2 feet) to work best, but once you’ve built it you can even sleep in it at night! Or, if sleeping in the snow isn’t your thing, enjoy having a hot chocolate in front of the fire and give a thought to the animals and plants surviving the season outside in the cold.
By Gabrielle Morey, SJMA Education Outreach Director
Falling Leaves: What’s Happening to the Trees?
Autumn is a beautiful time to be in the mountains, on public lands. The reds, yellows, and oranges we see in a land where we’re used to seeing greens and browns can be breathtaking. What are the environmental cues that are making this yearly phenomenon happen? And where does this color come from?
Why do Trees Lose Their Leaves?
In the Northern Hemisphere, autumn is generally known to occur during September, October and November. Our signals include fewer daylight hours and falling temperatures, not to mention other environmental cues such as birds migrating south or to lower elevations, our gardens finishing up their harvest, and of course, the changing colors and eventual drop-off of the leaves.
Why do trees lose their leaves every year? Doesn’t it take a lot of energy to make new leaves every spring? In fact, it takes plenty of energy for trees not to lose their leaves every year. Of course, some trees already do this – coniferous, or evergreen trees. Examples of these trees in our area include pines, spruce and firs. Coniferous tree leaves, also sometimes called needles (depending on the tree), must be specially adapted to deal with even the coldest winters. One of the main ways they are adapted to this is by being tough. Their leaves are tough and strong, as well as have many chemicals in them that aren’t very tasty to insects. Therefore they can ‘afford’ not to lose their leaves every year.
Deciduous trees that do lose their leaves every year do this for some very good reasons. For one, their leaves are just not adapted to survive the freezing temperatures of winter – they are much too delicate for that. Another reason is that by dropping their leaves they are getting rid of leaf-eating insects and their eggs and larvae. In fact, producing new leaves every spring is relatively ‘cheap’ for trees to do, considering what they get in return – the trees get to lose the old leaves that may have been damaged by weather, disease and insects, and are able to produce fresh, new leaves that can make food for the tree via photosynthesis.
What is it that makes the leaves drop? Tree trunks, branches and twigs can survive the winter, but delicate leaves aren’t so lucky. At the end of summer, the leaves are filled with sugar. At the base of each leaf is something called a separation layer. In the fall, the cells in this layer start to fill up with a cork-like substance, trapping the sugar in the leaves. Once this happens, water also cannot get to the leaves. The combination of this and the lack of sunlight makes the chlorophyll start to break down. Eventually the leaves fall from the trees, breaking off at this separation layer. Oak leaves are one exception to this, however. In oak leaves the separation layer never fully ‘separates’ the leaves from the twigs, and the leaves often stay on the tree all winter.
The Color of Things
For a good portion of the year, trees in our area are green. The green pigment in the cells of the leaves is chlorophyll. This chlorophyll is what allows the trees to be able to make food for the tree in the form of sugar. As the days get shorter, daylight is diminished and there is not enough light for photosynthesis to occur. The chlorophyll that was already in the leaves then begins to break down, and additional chlorophyll is no longer being produced, making the green fade from the leaves. Through the winter, trees rest from their food-making processes and live off the food that has been stored in the twigs and branches throughout the summer.
As the green fades from the leaves, orange and yellow appears. These pigments, called carotenoids, were actually always present in the leaves – we just couldn’t see them before because they were covered up by the green chlorophyll. Anthocyanins are the pigments that cause us to see red leaves. Anthocyanins are actually only made in the fall. This occurs because sugars are trapped in the leaves after photosynthesis stops. Not all trees make anthocyanins. It’s not clear why some trees do expend the energy to make anthocyanins. Some scientists believe it’s because it allows the trees to keep their leaves a little longer, allowing the nutrients in the leaves to go back into the tree for longer. Others think it’s because after the leaves fall on the ground and decay, it prevents other plants from growing and competing with the tree. The brown color that some leaves turn to is a result of wastes that are left in the leaves after the chlorophyll is gone.
It is speculated that the best fall colors appear when the spring has been wet, summer has been dry, and autumn has bright, sunny days and cool nights.
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