ent_drevobradecOf the many enchanting creatures that inhabit J.R.R. Tolkien’s Middle Earth, the ones that always made a great impression on me were the “ents.” These were trees, or rather, treelike beings. They mostly inhabited the Old Forest, and so resembled actual trees that at first the hobbits didn’t realize that the ents could speak and even, when provoked, move slowly but deliberately. Their role was to watch over and defend the forest from axes, fires, and any other threats from the inhabitants of that fictitious world. They were “very sturdy,” with large, toed feet that gripped the forest floor, skin like bark, bushy hair and mossy beards, and “slow, solemn…very penetrating” eyes.


At times, when in heavy woods, I have paused and looked up and around, imagining the imposing presence of the ents.


In the world we live in, we might well wish for ents, for something or someone intimate with the ways of the forest and the complexity of plant life, to defend or stand guard. Forests are so often under threat, not only from clearing, logging, storms, and fires, but from the very air, water, and soil the trees depend on to grow and thrive, resources the activities of humans so often and so unfortunately taint.


Like all living plants, trees actively absorb water and nutrients from the soil and convey these necessities to their cells. It is a simple system, in that nourishment comes in and growth and expansion result. Bear in mind, however, that the process can get disrupted or ruined if, say, the water is polluted by something as seemingly harmless as road salt or as unexpected as contaminated floodwater.


Without getting overly technical, then, here’s a more detailed description of how it works.


A tree’s underground system—which can be as broad or expansive as its top growth—often has a long taproot that goes deep into the earth, while other roots develop laterally to support it. Very fine root hairs at the root ends take in water and dissolved minerals from the soil. The tree then converts this enriched moisture into a liquid called root sap. Root sap travels up the trunk via a network of tiny tubes called “xylem” in a layer of wood termed “sapwood.” It moves on through to branches and twigs to supply every leaf.


As you may recall from biology class, foliage is the “food factory” of a plant, each leaf an individual photosynthesis unit. The leaves use moisture in concert with sunlight to remove carbon from carbon dioxide present in the air. Sugars are produced to nourish the tree, and oxygen is released as a byproduct. (Blocked sunlight and/or the presence of pollution, such as toxic fumes or a layer of ash on leaf surfaces can inhibit the process of photosynthesis.)


But there’s more. The activity on the cellular level inside these big plants is intensive. Sugars are conveyed through strings of cells out from the leaves. Outward and downward, to be precise, thus feeding the entire tree. These cells form a layer beyond the xylem, just beneath the tree’s outer bark; this layer is called “phloem.” (I remember my high-school botany teacher intoning in a low voice—it lodged in my memory—“food flow-em downward.” I always got that definition right on the tests!) In sum, healthy trees produce their own food.


The xylem and the phloem are not actually back-to-back. A very thin layer of vascular tissue called the “cambium,” which runs from the leaves to the roots, separates them. Close study has revealed that the cambium is not merely a buffer or a protective layer. It generates more xylem cells on the inside and more phloem cells on the outside.


As a growing season winds down in the fall, the xylem and phloem layers cease functioning. Dead, thus chemically altered (and often discolored) xylem becomes “heartwood” inside the tree’s trunk. Spent phloem, meanwhile, is incorporated into the tree’s bark. New xylem, generated in the spring months, will become the new year’s sapwood.


hollow treeHave you ever seen a partially or completely hollow tree, still quite leafy and alive? This is possible because these “veins” are in the outermost layer of the tree, just under the protective “skin” of bark. Every year, going through the cycle of generating new xylem, cambium tissue, and phloem, a tree adds a ring. The interior rings, literally relics from the tree’s sapling childhood, need not remain alive or intact for the overall plant to stand and survive. If they do, their role is supportive, but not essential. The important, sustaining activity is going on in the outermost layers. Climb inside a hollow tree someday, if you find one that fits you, sit down, look around, and ponder that.


When a tree’s rings are intact, of course, you can count them to find out how old it is. Those who have studied them have been able to gather information about seasonal events and climatic changes based on the condition, thickness, and contours of the rings. One year, the ring is thin and drought or other growth-inhibiting environmental stress is revealed; another year, there was a fire or lightning strike along one side, which eventually healed over. Rings may also reveal bouts with disease, insects, or manmade contaminants. In other words, the rings record the tree’s life story. You don’t have to cut a tree down to get this information, by the way; if needed or desired, a core sample no thicker than a chopstick can be extracted by an arborist without any long-term harm to the plant.


But back to the gas exchange. Plants absorb carbon dioxide from the air and the oxygen they release purifies the atmosphere so that we may breathe; large plants like trees accomplish this at a higher volume, of course, than an ordinary houseplant. Humans and other creatures are thus in an important, dependent relationship with plants: we release carbon dioxide when we breathe and they in turn release the oxygen we inhale. In the words of a forester, “This is why man can live a rich and happy life where there are trees. Where there are no trees, life is as barren as the desert.”


Reflecting on a treeless landscape, I am reminded of my first visit to Yorkshire, England. I had romantic notions of the place, thanks to the stories of veterinarian James Herriot (All Creatures Great and Small, etc.). My travel companion reveled in the rolling rural hills and quaint villages, but I was dismayed to view environmental devastation and a reduced human population. Firewood was precious, shade was scarce, the land was badly eroded, and any resurgent tree seedlings were nibbled down by sheep and livestock.


Some scientists, more acutely so in this era of global warming, believe that the best way to cope with pollution, erosion, and other environmental stresses is to spare existing trees and plant more trees. Perhaps trees can alleviate or even reverse the effects of the burning of fossil fuels, overpopulation, and destroyed forests (particularly swathes of tropical forests, an ongoing concern despite hue and cry from the outside world). In other words, more trees could counteract the damaging effects; trees could help save the world, help save us.


There are more benefits. On a physical level, trees offer cooling shade and shelter to our homes, streets, and parks, and to many animals. Insects live in their bark, leaves, and branches, and birds come to feed on these and to build homes (nests in the branches or holes in the trunk). An oak tree, just as an example, is the whole world to a squirrel—food, shelter, exercise, society. Many trees, from apple to persimmon to walnut, provide food for us and other creatures. Wood makes its way into our fireplaces and wood stoves, our homes, decks, porches and fences, our furniture, our musical instruments, and much more. Of course, trees are also a source of paper and related products. What other sort of plant can begin to offer this many useful resources?


If we are smarter, better stewards than the residents of Yorkshire, portions of the Amazon rainforest, and similarly devastated landscapes, we should be able to enjoy and use trees indefinitely. It is true that they are—as foresters have long contended—a renewable resource. If you’ve ever traveled into certain corners of Maine or Washington State, you’ve seen monocultural tree plantations, timber being cultivated like any other crop. Diverse, multi-species woodlots on public as well as private land can be prudently managed so select mature trees are harvested and their place is taken by up-and-comers. It takes time, savvy, and patience, but sustainability is certainly doable.


Given their importance to other living things, planting even one tree in a suburban yard or local park or greenbelt is worth doing. You’ll get to watch the small plant shoot upward and generate its first leaves and blossoms. Depending on what it is, you may be able to harvest fruits or nuts, or watch local animals enjoy its shelter or bounty. But you may not be around to see it become taller or wider than you, a stately specimen towering over its spot. If your family happens to move and you or one of your descendants is able to return one day to check on it, it can be a bittersweet thrill to view how much the tree has grown.


Tolkien’s sense that trees are sensitive and worried about their survival or indignant at abuses doesn’t seem so fanciful when you think about it. Although trees seem permanent and durable, they are vulnerable. We ought to be giving these grand, complex beings the space and respect they need and deserve—for their survival as well as our own.


<sidebar>Tree FAQs

What makes a plant a tree?

Trees grow radially as well as upward.

What is the main difference between a tree and a shrub?


What is the difference between a hardwood tree and a softwood tree?

Hardwoods are deciduous, such as maples and oaks and apple trees; they generally have denser wood and covered seeds (“angiosperms”). Softwoods (“gymnosperms”) are mainly evergreens, and have naked seeds, such as the pine nuts lodged in pinecones.

Which trees get struck by lightning most often?

Oaks. This could be due to the fact that many become large and long-lived, thus increasing their odds of being hit. If they are growing solo in a field or pasture, or next to water (which conducts), they make more likely targets, too. Oaks also have heavy, moist wood, rough, thick bark, and deep taproots—all presumed inducements.

Is there a Dutch Elm disease resistant elm tree?

Not totally, yet. Scientists and horticulturists continue to toil away on this dream, because elm trees are such handsome, practical plants. Resistant related species are sometimes touted; hybrids between them and the susceptible American elm have produced some admirable plants. As in any population, there is going to be an occasional resistant individual, and efforts continue to locate, evaluate, and clone such plants. The goal is successful propagation of genuinely healthy trees, followed by reintroduction.

What are some fast-growing trees?

Deciduous ones include Empress tree (Paulownia tomentosa), Lombardy popular (Populus nigra ‘Italica’) and willows (Salix); evergreen favorites are Leland cypress (Cupressocyparis leylandii) and dawn redwood (Metasequoia glyptostroboides). Bear in mind, however, that some of these can become weedy, and fast growth is not always strong growth.

What’s the best way to plant a young tree?

Dig a large hole, somewhat bigger than the root ball, and plant it at the same depth it was growing in the nursery. Current thinking is not to amend the soil in the hole, but instead to place the young tree in native soil, compelling it to expand into its new home. Handle the plant and its root system gently and water deeply and often its first season and beyond to encourage establishment.

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A version of this article originally appeared in Sanctuary: The Journal of the Massachusetts Audubon Society, Winter 2014.