The Forest Unseen: A Year's Watch in Nature by DavidGeorge Haskell Page B
Authors: DavidGeorge Haskell
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all living creatures, our own lives included, the flowers layer adaptation over history, creating the tension between diversity and unity, individuality and tradition, that makes the mandala’s immoderate blaze so compelling.
April 8th—Xylem
T he weather has been unsettled lately, dropping sleet on one day, then blazing with hot sunshine the next. The pace of life in the mandala follows these variations. On slushy days, leaves droop and the forest is silent except for the drumming of woodpeckers. Today, the sun is out and life has quickened, with revived greenery, a dozen species of singing birds, several small swarms of flying insects, and an early tree frog chirping from a low branch.
Last week, the forest’s green lay across the ground, a carpet of photosynthesis that ended at ankle height. Now the maples are unfurling leaves and dangling green flowers from branches. Like a tide rising, the green glow is reclaiming the forest from the ground up. The upward surge floods the mountainside with a sense of renewal.
Sugar maple branches hang over the mandala, and their new leaves block the sun’s rays, shading the understory. Of the hundreds of spring wildflowers, only a dozen remain; the maple has snuffed their spark. But not all the trees around the mandala are in leaf. The maple’s exuberance contrasts with the dour, lifeless pignut hickory that stands on the other side of the mandala. The hickory’s massive gray trunk rises straight to the canopy where it holds out dark, bare branches.
The contrast between the maple and the hickory expresses an inner struggle. Growing trees must throw open the breathing pores on their leaves, allowing air to wash the wet surfaces of their cells. Carbon dioxide dissolves into the dampness before it is turned to sugar inside theplants’ cells. This transformation of gas into food is the trees’ source of life, but it comes at a cost. Water vapor streams out of the leaves’ open breathing pores. Every minute, several pints of water are exhaled into the air by the maple above the mandala. On a hot day, the seven or eight trees whose roots penetrate the mandala send several hundred gallons of water out of their leaves as vapor. This reverse waterfall quickly dries the soil. When the supply of water is exhausted, the plant must close its breathing pores and cease growing.
All plants face this trade-off between growth and water use. But trees have another devilish layer of difficulty. By thrusting their leaves skyward they have become slaves to the physics of their plumbing systems. Inside each trunk lies the vital connection between earth and sky, soil’s water and sun’s fire. The rules that govern this connection are stringent.
Inside the trees’ leaves, sunlight causes water to evaporate from cell surfaces and drift out of breathing pores. As vapor wafts away from wet cell walls, the surface tension of the remaining water tightens, particularly in the narrow gaps between the cells. This tension yanks more water from deep in the leaf. The pull moves to the leaves’ veins, then down the water-conducting cells in the tree’s trunk, finally all the way to the roots. The pull from each evaporating water molecule is minuscule, like a breath of wind tugging at a silk thread. But the combined force of millions of evaporating molecules is strong enough to haul a thick rope of water up from the ground.
The trees’ system for moving water is remarkably efficient. They exert no energy, instead letting the sun’s power draw water through their trunks. If humans were to design mechanical devices to lift hundreds of gallons of water from roots to canopy, the forest would be a cacophony of pumps, choked with diesel fumes or run through with electrical wires. Evolution’s economy is too tight and thrifty to allow such profligacy, and so water moves through trees with silence and ease.
Yet this efficient water-lifting system has an Achilles’ heel. Sometimesthe rising columns of water
April 8th—Xylem
T he weather has been unsettled lately, dropping sleet on one day, then blazing with hot sunshine the next. The pace of life in the mandala follows these variations. On slushy days, leaves droop and the forest is silent except for the drumming of woodpeckers. Today, the sun is out and life has quickened, with revived greenery, a dozen species of singing birds, several small swarms of flying insects, and an early tree frog chirping from a low branch.
Last week, the forest’s green lay across the ground, a carpet of photosynthesis that ended at ankle height. Now the maples are unfurling leaves and dangling green flowers from branches. Like a tide rising, the green glow is reclaiming the forest from the ground up. The upward surge floods the mountainside with a sense of renewal.
Sugar maple branches hang over the mandala, and their new leaves block the sun’s rays, shading the understory. Of the hundreds of spring wildflowers, only a dozen remain; the maple has snuffed their spark. But not all the trees around the mandala are in leaf. The maple’s exuberance contrasts with the dour, lifeless pignut hickory that stands on the other side of the mandala. The hickory’s massive gray trunk rises straight to the canopy where it holds out dark, bare branches.
The contrast between the maple and the hickory expresses an inner struggle. Growing trees must throw open the breathing pores on their leaves, allowing air to wash the wet surfaces of their cells. Carbon dioxide dissolves into the dampness before it is turned to sugar inside theplants’ cells. This transformation of gas into food is the trees’ source of life, but it comes at a cost. Water vapor streams out of the leaves’ open breathing pores. Every minute, several pints of water are exhaled into the air by the maple above the mandala. On a hot day, the seven or eight trees whose roots penetrate the mandala send several hundred gallons of water out of their leaves as vapor. This reverse waterfall quickly dries the soil. When the supply of water is exhausted, the plant must close its breathing pores and cease growing.
All plants face this trade-off between growth and water use. But trees have another devilish layer of difficulty. By thrusting their leaves skyward they have become slaves to the physics of their plumbing systems. Inside each trunk lies the vital connection between earth and sky, soil’s water and sun’s fire. The rules that govern this connection are stringent.
Inside the trees’ leaves, sunlight causes water to evaporate from cell surfaces and drift out of breathing pores. As vapor wafts away from wet cell walls, the surface tension of the remaining water tightens, particularly in the narrow gaps between the cells. This tension yanks more water from deep in the leaf. The pull moves to the leaves’ veins, then down the water-conducting cells in the tree’s trunk, finally all the way to the roots. The pull from each evaporating water molecule is minuscule, like a breath of wind tugging at a silk thread. But the combined force of millions of evaporating molecules is strong enough to haul a thick rope of water up from the ground.
The trees’ system for moving water is remarkably efficient. They exert no energy, instead letting the sun’s power draw water through their trunks. If humans were to design mechanical devices to lift hundreds of gallons of water from roots to canopy, the forest would be a cacophony of pumps, choked with diesel fumes or run through with electrical wires. Evolution’s economy is too tight and thrifty to allow such profligacy, and so water moves through trees with silence and ease.
Yet this efficient water-lifting system has an Achilles’ heel. Sometimesthe rising columns of water
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