“Stand cool and composed before a million universes.” -Richard Powers, The Overstory

I have a cross stitch picture of a birch tree hanging on my study wall. The crown of the tree is being driven to the right of the trunk by a gale. The branches are blown like a full sail across the frame, whipping and cracking like waves. The leaves are three different shades of green, and a few have just separated from the leaf scar, frozen mid-air before they blow away on the gust. There is a subtle, abstract suggestion of three low hills in the distance behind the trunk, and a few clumps of grass in the foreground, but other than that it is just the solitary tree bent under the force of the wind in some nameless landscape. When I sit down, my focus is always drawn to the tree, or more so the energy that’s moving through it. It is the perfect illustration of durability, a simple Zen-like durability. My imagination is captured by the tree’s ability to move in the world around it, and still remain firm in its place. Fixed and fluid. Bent, not broken. The essence of the piece is that this tree is the whole world, or rather that it’s harnessing the whole world. And I remember that the tree continues to slowly grow outward into the landscape. It acts and reacts. The roots curve with the shapes of the earth. The wind and the rain flow through it, these harsh elements shape it. The tree absorbs these giant forces of weather and world, and dissipates them gracefully, with a few scattered leaves, like ripples on water. Trees are like the surface of a lake in that way, they reflect their surroundings with mirror-like quality, but it is impossible to see the actual depth of them in that superficially still picture.

Trees are moving all the time, reacting internally and externally to everything that’s happening in their environment. Root hairs probe through the dark mucus of the rhizosphere, plunging into available water and nutrients incrementally; or even desiccating and dying in parched soil. Veteran trees decay and break down internally, housing vast networks of organisms and organic matter where there was once a static mass of dead heartwood cells. They are a bridge in this way between life and death. We may see an owl or a raccoon peak out of a hollow where a large scaffold limb once grew. Walking along a wooded path the other day, I observed a micrathena spider spinning its web between the dead twigs of a striped maple and the small trunk of an oak across from each other on the path. I was reminded that life is suspended in the space between trees. Trees have an opportunistic character to react to death and decay by creating opportunities for life. A samara is cast from the upper crown of a maple, and may land in the union of a nearby walnut tree down slope, or in a crinkle of decaying leaves on the forest floor. I have found young birch seedlings growing on top of old uprooted hemlocks. Trees are like the stands holding sheet music for the song that nature plays. A carolina wren lands on a nearby dogwood and sings out: teee-cher, teee-cher, teee-cher, teee-cher. And we learn. Leaves flutter and swirl atop their petioles, riding on a passing wind, which vibrates across tertiary and secondary branches and dampens all the way through scaffold limbs, wiggling down to the root flare. Cells stretch and twist in accordance with these reverberations. Growth rings bend and dip with that weight of dynamic motion. Buds break and leaves unfurl, building a complex scaffolding network for capturing sunlight. There is the constant creep of water molecules up through the xylem as transpirational pull replaces drips of water from the soil into the atmosphere, and oxygen seeps out from stomata to give living things breath. Trees are a conduit of life, in constant motion, conducting the business of nature, bending and breaching and exploding forth. Trees are something to land on. It is their quiet nature to invite things in. It is in their quiet contract to give everything back.

A pruning cut causes physiological reactions. Tissue is exposed to air, and the course of physiology will depend on a multitude of factors such as cut size, environment, tree species and tree age. When we cut through a branch, our saw blade passes through the bark, phloem, cambium and xylem. Each of these tissue parts has a specific function, and a reaction will take place at each specialized cell grouping. Callus forms from the secondary meristem of the cambium. As callus grows over the pruning cut, those cells that spill out continue to differentiate into specialized conducting tissue. Where flow was once cut away, it now rushes back. But once bark is removed from the exterior of the tree like in a pruning cut or other type of wound, air is introduced and therefore wood tissue is colonized by fungi and bacteria. Tyloses plugs up vessels and fungi begins to decay wood, this is the race of survival that wars on in the sapwood symplast. More sunlight will penetrate onto the interior crown when we prune because of the loss of leaf material. Less photosynthetic capacity in leaf area may trigger more photosynthetic potential in axillary buds popping from increased sunlight penetration. Apical growth will be triggered at the terminal points of lateral branches. Root pressure changes. If we reduce branch length, weight distribution changes along the axis of the limb, and lignified levels will fluctuate in cell walls (tension and compression). Pruning then channels a flood of chain of reactions. The tree system, whether young or old, is loaded with reactive potential. And by pruning too much we can deactivate this potential, and crush that hopeful vigor. Removing too much energy making and storage capacity can tip the scales towards crown loss and decline. With no bank to draw from, the river runs dry. The lake dries up. With a keen eye, we can look at trees and they will tell us stories about the way that they have reacted in the past with their present posture. We can see how they lived and how they died.

Good observations can lead arborists to develop sound objectives in arboriculture. Our prescriptions are focused on reactions. We want to promote good reactions, and we want to avoid bad ones. Shigo advised us to touch trees, in order to listen to and feel what they tell us. Those wonderfully healthy trees are the ones with the world flowing through them, the breeze, the rain, the birds on the branch ends. Lush green leaves that change gold in autumn reassure us of a healthy year, and a brisk autumn seems fresh after a long summer; but scorched and chlorotic margins advertise a warning. Trouble is knocking. So too does life flow through the dead and dying, the trees leaning and toppling over, and wilting away. I think every tree is really straddling that gray line between this life and the next one. Trees are time machines like that, throwing us back and forth between the things we can’t change and the things we can. We race across that stillness. As arborists we are like a time traveler, caught in between a tiny world, and an enormous one.