Like a Tree. Jean Shinoda BolenЧитать онлайн книгу.
outside agencies required—and to operate for good measure as an independent living creature through all phases of growth is beyond anything that human engineers have achieved. (2006, p. 75)
What Exactly Is a Tree?
Trees are arboreal perennials: they have a columnar woody stem with branches growing from it. The height varies according to the specific species, environment, and various other factors, though normally they reach a height of twenty feet (six meters) or more. The shape and general development of a tree are so characteristic that the category also includes species of lesser size, such as dwarf trees.
In the delightful way that the English have with words, Colin Tudge begins his answer with what every child knows: “A tree is a big plant with a stick up the middle” (The Tree, p. 3) and proceeds to be eloquent and scientific, a small part of which I paraphrase and pass on here.
Some two to three billion years ago, a layer of vegetation grew upon barren rocks—a slime perhaps no thicker than a coat of paint, made of bacteria, molds, mosses, lichens, algae, and fungi. Chlorophyll in algae made the slime greenish and photosynthesis possible: the energy from sunlight (photons) was used to make sugars and stored by algae. This was the significant first step. Stalks formed slowly, slowly over many, many millions of years, grew from nubbin to matchstick to become ferns that proliferated and grew to enormous size in the Carboniferous period, which began about 350 million years ago. This was a time when giant forests of huge tree ferns covered the Earth. These tree ferns removed prodigious amounts of carbons from poisonous gases, storing it in their leaves and stalks. After millions of more years went by and layer upon layer fell into decay, pressure and time transformed these vast fern forests into coal. Removing carbon dioxide and releasing oxygen, these giant tree fern forests made the air breathable. They also made it possible for more sunlight to reach the surface of the Earth through the clearer air.
The fern forests became the womb and the nursery of the first trees. As John Stewart Collis, another English author phrased it, “In these glades was matured the idea of not falling down” (Collis, The Triumph of the Tree, 1954, p. 10). The ferns rose and fell, over and over again, producing stalks and branches that grew eventually to be the size of trees. In their midst, some 290 million years ago, a more energy-efficient form of plant life, which had woody trunks and branches, appeared. Wood tree trunks are structurally stronger than stalks, and they have roots that anchor the tree in the ground. Tree trunks provide a two-way conduit of water and nutrients from roots to leaves, and from leaves to the whole tree. As a tree grows above the ground, its root structure grows also. In good, deep soil, some species of trees can have as large a circulatory root system below ground as the visible branches and leaves.
The root system of trees continues to have a key role in transforming rock into soil. This process began when the planet was lifeless rock, with a thin layer of algae, mold, lichen, and fungi. Soil is made from rock that disintegrates into dust and releases minerals, plus decaying organic matter, oxygen, and water. Trees draw from and contribute to making more soil. Their roots break up and aerate rock and hard clay. Dropping leaves provide organic matter. Their leaves release water vapor and oxygen into the atmosphere, drip water into the ground below, and provide shade that prevents evaporation. Trees create the conditions for ground-covering plants to grow under them. Tree roots hold the soil down, preventing runoff after rain and keeping strong winds from carrying it away. Trees create watersheds, the source of water to feed streams and rivers. When huge areas of forests are clear-cut for timber or burned down to raise cattle, the ecological systems supported by trees—from roots to leafy canopies—are also destroyed, affecting all forms of life that once thrived there, as well as the quality of the air, soil, and water in the immediate area and far downstream.
Every large tree has an ecosystem of its own, a sphere of influence in its immediate environment. I began to think about this after my Monterey pine was cut down. There were observable consequences, beyond its absence. The resident squirrel got displaced. More direct sun instead of partial sun and shade changed what would thrive in the half dozen terra-cotta planters that I planted with annuals. Direct sun in spring and fall, morning fog in the summer had been ideal for the bright, colorful impatiens that I had planted for years, exchanging them for cyclamen as autumn approached. The tree had also sheltered many plants from the wind, which I next discovered. For the first time, in the absence of shade, I planted sun-loving petunias, which initially grew very fast and had to be watered often. Then came the summer fog, and the petunias became immediately pathetic, the blooms overnight becoming limp and mildewed. A slow-growing vine went into overdrive, sending out waving tendrils by the foot that now needed to be cut back often, before they could cover or strangle nearby rhododendrons. Now unprotected from the direct sun, rhododendron and camellia leaves became sunburnt in unusually hot weather. The side of the hill on which this particular tree had thrived for forty or so years has very poor soil; the dirt is mainly gravel and sand and very hard. Yet the ground cover and established shade-loving flowering plants and a maple tree did well, with virtually no watering. The pine needles had been a water-dripping system. Not just for itself, but also for its tree neighbors. So much so that when I went out to get the morning newspapers, the walk beneath its branches often looked as if it had rained during the night. The pine tree had been the center of an ecologically sustainable little island, which now requires watering.
Invisible to me was the ecosystem underground. Trees are part of a mutually beneficial community in all directions. Trees are a habitat for the plants, insects, birds, and animals in their vicinity, but an even closer bond is formed with the fungi and bacteria that are intimately connected to the metabolism of the tree. They eat the sugars that the tree makes and bind the hydrogen that the tree needs. Bill Mollison, the originator of permaculture, a sustainable ecological design inspired by observing rain forests, described how bacterial colonies on the leaves of trees are carried aloft by the wind high into the clouds, where ice crystals form around them, and as they get heavier and fall, they seed the clouds and cause rain to fall on the trees. The rain that falls through the tree canopy is now rain-bath water, a rich nutrient soup that washes off the minerals that were left on the leaves by evaporation, providing these nutrients for the ground cover, the little plants under the trees, and soaking into the soil, from which it will be pulled through the roots, the ends of which are covered by bacteria that are a two-way selective filter, and up the xylem of the tree to the leaves. Forests of trees keep the rain going, which is why all huge forests, whether in the tropics or on the northernmost edge of the continents, are rain forests.
Two Kinds of Trees
My tree was a conifer (conifer means “cone-bearing”), in the tree family lineage that began 290 million years ago. Conifers are familiar trees, known to us as firs, spruces, pines, cedars, redwoods, cypress, podocarps, yews, and junipers. They originated in and continue to survive in poor soil, with extremes of weather from tropical to desert, to almost arctic. Among the conifers in California are coast redwoods, the tallest trees in the world, and the bristlecone pines, which are the oldest. They comprise the vast boreal forests in Alaska, Canada, Scandinavia, Russia, and Siberia. They thrive in places where conditions are difficult, including in areas where fires are common. They are survivors and pioneers—trees that move into devastated areas and grow where other trees do not.
The conifers are one of the two large tree categories that make up 99 percent of all trees: trees without flowers (conifers) and trees with flowers (the angiosperms). Angiosperms differ from conifers in their sexuality. The female ovule is completely enclosed within the ovary, and the male gamete must be carried to it via pollen tubes. Uniquely, angiosperms practice double fertilization. This is a very brief summation; left out are definitions and explanations, the various means of union and procreation, and how this contrasts with conifers. Suffice it to note that the obstetrics and gynecology of the two categories differ. The angiosperms are a huge universe of flowering plants (300,000 species), among which there are trees. The surmise is that flowering trees with woody trunks evolved from flowering plants, with missing links. Also not known are when, where, and how angiosperms originated.
Broadleaf trees are angiosperms: they include acacia, maple, elder, baobab, alder, aralia, birch, hickory, hawthorn, laurel, eucalyptus (gum), linden, olive, beech, banyan, fig, sycamore,