We have our reasons for planting trees: their fruits, their shade, shelter from the wind, a bit of privacy, something to fill that awkward gap by the driveway. But as often as not the trees outlive, or outgrow, our reasons for planting them. Oddly, that doesn't seem to matter. As with our teenagers, their ungainly stature fills us [for the rest of this story, see the December 2007 issue of Down East]with an affectionate sort of awe.

The old apple leaning over the fence hasn't produced a decent crop in years. Yet we treasure its gnarled and venerable presence, we can't imagine that corner of the yard without it. The white pine we planted as a screen is twice as tall as the house now, its trunk straight and bare up to the attic windows - but by God, what a magnificent thing, even its fallen needles have a transient beauty about them. And the maples, pushing up the sidewalk but flaming scarlet in autumn . . . the yew that swallowed the corner of the porch . . . the row of arbor vitae that once stood like toy soldiers but now have a battered, asymmetric dignity, like veterans of a long campaign - none of those much resemble the nursery-grown saplings of a decade or two ago. They're so much cooler now. They've become, in the parlance of garden design, "specimens." Probably they'll outlive us; and paradoxically, many tree-lovers find a strange solace in that.

Winter is the best time to see trees. I mean, to really see them: Their true shapes, their daunting scale and sometimes curious proportions. Their relations to one another, to the land around them, to human-made features like walls and barns and SUVs, which they nonchalantly throw into perspective.

Some trees you only notice in winter, like the slim conifers whose dark, tapering spires are lost in woodland shadows until the deciduous muscle-boys get naked. Others, you never fully appreciate until you've seen them silhouetted against snow clouds, bathed in eerie winter half-light - at such times, they seem to emanate strength and reassurance, like sentinels guarding the earth against some supernatural intrusion.

Driving around Maine in winter, I find myself doubting the perfectly sound and logical arguments put forward by, say, the Arbor Day Foundation as to why trees are good for us. Because by winter most of those considerations - shade, fruit, privacy, what have you - have been gone for months and are hard now even to imagine. Yet the trees remain, more conspicuous than ever, more starkly beautiful. And their presence feels, if anything, more welcome, more important, more necessary than at gentler times of the year.

Which is why we plant them, I think. Because somehow, we sense that they're needed.

They're an indispensable part of the Maine landscape. No pines, no Pine Tree State. Certainly there are issues of utility here - from the traditional forest industries to the latest buzz around ecotourism - as well as issues of aesthetics, philosophy, and environmental stewardship. But ultimately I think our feeling for trees comes from someplace deeper than any of that.

The biologist E. O. Wilson proposes the term "biophilia" to capture the striking affinity we feel for other forms of life. He suggests that somewhere within us, maybe encoded in our genes, is a deep awareness that we depend on the whole interlocking web of life to support our own well-being. In evolutionary terms, this biophilic sense must have aided the survival of our distant ancestors - perhaps by helping them choose safe, sustaining places to settle and to procreate, thus giving rise in the fullness of time to us, their distant progeny, contemplating nature from behind our double glazing. We've inherited that innate faculty, and maybe it will stand us in good stead as we face the challenges to our own survival.

This isn't a treatise in deep ecology. I'm not suggesting that, subconsciously, we want our backyards to revert to Thoreau's Maine woods. The winter landscape has a different lesson to teach us.

If you take a serious look at our countryside in winter - not by trekking for miles through the forest, but simply casting a thoughtful glance out the window of your car - you won't see much in the way of pristine nature, nor of mindless despoliation. What you'll discover is evidence of a partnership, long-standing, and by no means hostile, between ourselves and the rest of the living world. The proof is in the trees.

We could start at the corner of my two-acre building lot, which was for many decades the corner of a vaster piece of land. To mark it, a red oak was planted, or maybe a seedling was just left to grow. Today, though younger trees have filled in around it, that once-solitary oak stands apart in an open glade it has made for itself with its own overspreading shadow. It's decades older than anything else around it. I find its presence reassuring: proof that we Mainers have lived here for quite a while without screwing every single thing up.

Less than a mile off, another oak of this species stands before a ramshackle bungalow in an otherwise empty lawn. With no competition for sunlight - a circumstance only made possible by human connivance - it's grown twice as wide as tall, spreading to such an improbable extent you can't quite believe the limbs are able to support themselves. Only God can make a tree, they say, but no tree God made all by Himself ever looked like this.

A state highway runs nearby, past homesteads dating from the earliest local settlement. As usual, many of these places have their borders marked in stone, but some also have boundary trees. In one spot, driving north, you come over a hill and look across a dip in the land to a hillside opposite where closely planted beeches line the crest of a grassy slope. For a few weeks in late winter, if you happen to be commuting home around sunset, these trees seem to leap up before you with the sun caught in their delicately woven branches, the low-lying foreground in shadow, and a dark bay seething beyond. Words pale before a sight like this. It never would've happened if nature had had its way.
Then there are places - you've seen them, I guess - where a long-vanished house is memorialized by the trees that once surrounded it, towering now like giants in a squarish huddle, shading a ghostly porch that has passed from human recollection.

I love to discover things like this. I love to browse the Maine landscape like an old scrapbook, its colors weathered to monochrome, page by page affording glimpses into other lives but never the whole story, because the story is so long that its earliest parts are forgotten, and its later twists still revealing themselves.

I've made a few contributions myself, around my newly built cottage: four oaks of assorted Southeastern and Mid-Atlantic provenance, which I'm betting will hold their own against the torrid summers to come, and a bodyguard of other tough breeds. It's all speculative, of course. But I think someday they'll amount to something.