Where is the heart of life in a winter wood?

A winter storm on the Dead River and its red and white pines.

A winter storm on the Dead River and its red and white pines.

 by Scot Stewart

“Stark skeletons of wood, the trees stand solemnly on the hill waiting to take their licks from the winter wind, so aware, yet so unafraid of what they deeply understand.” — Anonymous

Nature looks dead in winter because her life is gathered into her heart. She withers the plant down to the root that she may grow it up again fairer and stronger. She calls her family together within her inmost home to prepare them for being scattered abroad upon the face of the earth. — Hugh Macmillan, “Rejuvenescence,” The Ministry of Nature, 1871

There is a stillness in winter woods. The songs of the wood’s summer resident songbirds, and the sounds of bees, flies, wasps, cicadas, frogs and toads are gone. The gentle, and at times not so modest, flapping of leaves in stormy winds is absent as well. Except for the occasional roar of storm-whipped branches and waves on the Big Lake, it’s as though the land is in a big sleep.

Freezing winter conditions offer challenges to survival for all life still on the horizon in Upper Peninsula winters, especially those unable to control their own body temperature. It is all due to water. Most substances condense as they cool down. Water is an exception. Anyone who ever put a canned or bottled beverage in the freezer for a quick cool down and forgot about it knows. As water freezes, it expands. If that water is inside a cell, the crystals eventually stretch through the cell membrane, the envelope holding the cell’s contents together, and destroy it and the cell.

Plants can’t migrate or burrow into the ground (although some parts growing there can adjust to freezing temperatures or create their own heat). Left to find other plans to deal with freezing temperatures, they have developed a number of major, distinctive strategies to make it through the winter months and deal with these threatening conditions. These strategies vary from the extremes of undergoing chemical changes in the needles and cones of conifers to avoid ice crystal damage in needle cells, to the extensive seed production of annuals before they just freeze up and die. In between are broadleaf deciduous trees dropping their leaves in fall to perennials with all sorts of tricks to survive. The trees’ large leaves produce high levels of photosynthesis products in summer, then undergo a massive transformation each fall and spring as leaves are shed for winter and replaced with new ones. At the top end are the most creative–perennials. They store large amounts of nutrients and energy in roots or tubers, lose their above-ground leaves and stems during the winter, then replace them in the spring with new ones. These are often combined with other unique adaptations.

Conifers—cedars, junipers, firs, spruces and pines—take a different approach to winter. They keep their photosynthesis machines on board, retaining their scales and needles—their leaves, usually for two or three years. There is a rotation process, so a fraction of needles are shed in a season giving the impression they are not really shedding until the ground below reveals the whole story. They rely on water shifts in their cells to avoid the damage caused by ice crystals growing within and causing cell damage. Their tissues create spaces between the cells when water is stored outside them, freezing outside the membranes and concentrating the remaining fluids within in a liquid similar to antifreeze. The leaves themselves are slender, usually coated with thick waxes and have small water stomata, opening on their undersides, to reduce water loss.

Unfortunately, winter is basically a drought for these plants. With the cold temperatures, water is unable to move up from the ground. Unable to get more water to the branches, water has to be conserved. Problems arise with warmer temperatures on balmy winter days. Water in the needle tissue begins to turn to vapor and can be lost through water stomata, causing dehydration. Narrow, waxy needles reduce that water loss.

A close up of milkweed seeds.

A close up of milkweed seeds.

Slender needles and scales reduce the surface area for sun absorption during photosynthesis, so conifers usually grow slower than deciduous–think about fast-growing aspens. The shape does help shed accumulating snow. Additionally, their tree shape, vaguely to acutely triangular, also assists in reducing the snow load on branches, as snow can slide off. This may help explain why white pines often look so battered sometimes. Their horizontal branches and dense clusters of needles—five to a bunch—trap more snow than most conifers and suffer plenty of broken branches, reshaping the tree tops.

The exception to needle retention among conifers is the Larix or tamarack family. For the eastern tamarack, daintier needles turn brilliant yellow in the autumn and fall off. The needles contain fewer waxy chemicals needed to make it through the winter, so they can photosynthesize more during the summer, then drop off for winter when conditions can cause more damage to them.

Broadleaf trees like maples, oaks and aspens drop their larger, more delicate leaves each fall, eliminating the need to develop water loss mechanisms on the outside of the leaves, and water movement strategies on the inside. Special cells, called abscission layers, develop between the leaf stalk, the petiole and the branch, cutting off water to the leaf and protecting the scar at the point of attachment. Trees simply have to ante-up in the spring and grow a whole new set of leaves. Water still in branches and the trunk travels back down the phloem tissue to the roots to be stored until springtime.

Annual plants include weeds like crab grass and chickweed, flowers like sunflowers and many garden plants like beans, squash, corn, melons and tomatoes. Many are large, fast-growing plants, relying on an abundant supply of water to help them grow—sometimes up to ten feet in one growing season. Annuals put large amounts of energy in seed production, especially sunflowers, beans and corn. Melons, squash and pumpkins add even more into the production of fruits surrounding their seeds. With a huge investment in large seeds, surrounded with large amounts of stored energy, these plants can afford to “let go” at the end of the growing season and simply die, banking on the future of the species being ensured with many seeds to start again the following spring.

One slight variation on this theme, the biennial takes this a step farther but waits a second year before producing seeds. Mulleins, carrots and Queen Anne’s lace produce lots of leafy foliage their first summer, sending up their photosynthesizing leafy tops and storing large amounts of food in starchy roots. The following summer, this stored food is used to produce a large number of usually small seeds.

Some plants take fewer risks, relying on two different strategies to double their survival chances. Perennials produce good seed crops but also produce large tap roots, often extending down several feet. The number of seeds perennials produce each year varies. Grasses may produce only one or two seed clusters, maturing only at the end of summer. Dandelions may produce seeds throughout the growing season, being among the first and last each year. Spotted knapweed can produce hundreds of thousands of seeds on the many flowered branches of older plants.

Besides their annual seed production, these plants also develop large tap roots capable of storing significant amounts of food for the following year, and in the case of some prairie grasses, long enough—up to sixteen feet—to reach guaranteed water supplies. Milkweed plants are among the most versatile of plants when it comes to reproduction. Besides producing hundreds of parachute equipped brown seeds, they can produce from rootstock, diving deep below the soil surface, and by horizontal roots capable of pushing out new stalks far from the original. One plant can effectively produce a whole stand. Rubbery stalks all die back each fall, but sturdy below-ground roots will bring back these expanding stands the following spring.

Two common milkweed pods

Two common milkweed pods

Then there are some perennials capable of adding an interesting twist to the entire show. Jack-in-the-pulpits are members of the Arum family. Living in damp soil in shady areas, they are often overlooked by most. In their initial years, they are small, very nondescript plants, producing a small vase-like flower with green, cream and occasionally brown stripes, with a large spadix (the Jack) in the center of the flower (the pulpit) under the trio of leaves. A smaller amount of energy is needed to produce male flowers on the spadix—one producing only pollen—so the plant is strictly male. As the plant grows each year, larger leaves send more food to be stored in the tap root. This eventually allows the plant to produce flowers of both sexes on the center structure and with them the potential for a yield of a bunch of bright red fruits each with around five seeds, essentially becoming female plants with some male flowers. The flowers are not self-pollinating, so the plants rely on insects for fertilizing the female flowers.

With a tough winter ahead, plants have already made the changes they need for the challenging months. Leaves have withered, turned colors and dropped. Water has run back with sugars to the roots. Water has been pushed out of cells, readying needles for the freeze ahead. Amazing changes, clear in some, only partially visible in others. Roots and seeds lie waiting, through the coldest, snowiest and iciest of winters, patient and resolved to be ready for the spring to come.

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