by Jeff Tietz
From a tree’s perspective, excessive heat may be as deadly as lack of water.
To photosynthesize, a tree opens pores in its leaves called stomata and inhales CO2. Solar-charged chemical reactions then transform the CO2 into carbohydrates — the raw stuff of leaves and wood. During this process, a fraction of the tree’s internal water supply evaporates through its stomata, creating the negative pressure that pulls water from the soil into the tree’s roots, through its trunk and up to its canopy. But heat juices the rate at which trees lose moisture, and that rate escalates exponentially with temperature — so small temperature increases can cause a photosynthesizing tree to lose dangerous amounts of water.
“Forests notice even a one-degree increase in temperature,” says Park Williams at Los Alamos National Laboratory.
In the death scenario, the sky sucks water from the leaves faster than it can be replaced by water in the soil, and the resulting partial vacuum fatally fractures the tree’s water column. If a tree closes its stomata to avoid this, shutting down photosynthesis, it risks starvation.
Ultimately, the tree’s cellular chemistry will fail, but it will often die before that, as its defenses fall; the complexly toxic sap that repels predatory insects dries up.
Many insects can detect diminished sap levels within tree bark by scent — they smell drought stress and pheromonally broadcast news of deteriorating tree health. Other defenses – against microbes, for example — may also be compromised.
A hotter climate generally means more insects.
It also means more, and more intense, wildfires.
For decades, all over the planet, heat-aggravated drought has been killing trees: mountain acacia in Zimbabwe, Mediterranean pine in Greece, Atlas cedar in Morocco, eucalyptus and corymbia in Australia, fir in Turkey and South Korea.
In 2010 a group of ecologists published the first global overview of forest health. They described droughts whose severity was unequaled in the “last few centuries” and documented “climate-driven episodes of regional-scale forest die-off.”
Because global warming outpaces evolutionary adaptation, the question is: Can trees survive as they are?
The conifer forests of the Southwest United States, if climate projections are even minimally accurate, cannot, but what about the rest of the world’s forests?
That’s a critical question, because forests cover more than a quarter of the planet’s land, and they help stabilize the climate by pulling immense quantities of CO2 out of the air.
In August 2011, a team of scientists led by Dr. Yude Pan, a U.S. Forest Service researcher, reported that between 1990 and 2007, forests sequestered about 25 percent of all greenhouse-gas emissions — everything not in the air or seas.
Climatologists worry that if forests across the planet deteriorate, they could, on balance, begin releasing as much carbon as they absorb.
One of Pan’s collaborators, Dr. Richard Birdsey: “If the carbon sink in forests fails, a simple speculation is that global temperatures would increase proportionally to the increase of CO2 concentration, so about 25 percent above current climate projections.”
“The more forests die, the less carbon they take out of the air, the warmer it gets, the more forests die,”
says Dr. Nate McDowell at Los Alamos. “It’s a thermostat gone bad.”
The better we understand climate change, the more we seem to find that warming begets warming in unexpected and self-amplifying ways: Implacable heat engines materialize and run independently of all human effort.
There are an estimated 1 trillion metric tons of frozen carbon in the soils of the Arctic region — a century’s worth of global emissions, twice the amount stored in the global forest, another few Industrial Revolutions.
As the planet warms, permafrost thaws and decomposes, sending carbon into the air and further warming the planet. Higher temperatures also kindle increasingly intense and frequent wildfires in high-latitude forests, to quadruple effect.
And fire releases carbon directly; it burns off the insulating upper layer of vegetation, exposing more permafrost to warm air; it blackens the trees and land, which consequently absorb more solar radiation; and its soot can settle on and darken snow and ice sheets to the north, which then also absorb more solar radiation.
By the end of the century, the woodlands of the Southwest will likely be reduced to weeds and shrubs. And scientists worry that the rest of the planet may see similar effects.
Trees Cry Out
The Longevity of Trees
A Living Miracle
Du Bon Usage des Arbres
Abbott Thayer was a lifelong wildlife advocate whose artistic focus never strayed far from his personal fascination with the natural world.
On 11 November 1896 he made an appearance at the Annual Meeting of the American Ornithologists’ Union in Cambridge, Massachusetts arriving at the Harvard Museum of Comparative Zoology on Oxford Street bearing a sack of sweet potatoes, oil paints, paintbrushes, a roll of wire, and two new principles of invisibility in nature that together formed his “Law Which Underlies Protective Coloration.”
In his afternoon open-air lecture, Thayer argued that every non-human animal is cloaked in an outfit that has evolved to obliterate visual signs of that animal’s presence in its typical habitat at the “crucial moment” of its utmost vulnerability.
Thayer arrived at camouflage inadvertently, in the process of pursuing art.
As a student, he had learned that any shape drawn on a flat surface can be given volume and dimension by a venerable process called shading. This is reliably achieved by rendering the shape lighter on the top and gradually darker toward the bottom.
As we know from current brain research, this takes advantage of an inborn visual tendency called the top-down lighting bias: when we look at anything, we default to the assumption that its light source is coming from overhead.
Observation then enabled him to realize why so many animals have light colored bellies with darker coloring toward the tops of their bodies. The effect is the inverse of shading.
Appropriately, it became known as countershading, because the effect counteracts the shadows resulting from cast sunlight, making an animal look less dimensional, less solid, less “thing-like.”
Though some of Thayer’s other proposals have been disregarded, countershading is a widely accepted biological principle today, and stands as the artist’s most significant contribution to the natural sciences.
By 1896, Thayer was increasingly inserting himself into what was a longstanding debate over the origins, effectiveness, and pervasiveness of protective concealment in the natural world.
After the publication of Charles Darwin’s Origin of Species in 1859, animal coloration—both its origins and its role in animal behavior—had become a key locus of debate among natural historians, artists, and the lay public.
Prior to this period, naturalists had noted instances of animals’ blending in with their backgrounds. It seemed remarkable that God had “dropped” them into place just so—“nature by design.”
By contrast, in an evolutionary model, there was a gradual “fitting together” over time. Evolutionary theories, both Darwin’s and that of his colleague Alfred Russel Wallace, presented a range of explanations for animal colors. Darwin emphasized interrelations between the sexes as the cause of the showy coloration found in the male of many species; females chose the more colorful males for mating.
Wallace, studying the colors of many insects, interpreted bright hues and complex patterns alike as either warning signals to potential predators, modes for assimilation in the environment, or mimicry of other, more dangerous, species.
Meanwhile, philosopher-psychologist William James, a friend of Thayer’s and a fellow birder, discussed the experience of bird watching in his 1890 Principles of Psychology, describing the study of illusions, or so-called “false perceptions,” as critical in efforts to understand human apprehension of depth, color, and movement.
Thayer’s New Hampshire summer home, to which he and his family relocated around 1900, was transformed into a year-round laboratory for studying protective coloration.
His communion with nature permeated the entire household. Wild animals—owls, rabbits, woodchucks, weasels—roamed the house at will. There were pet prairie dogs named Napoleon and Josephine, a red, blue and yellow macaw, and spider monkeys
Soon, his wife Emma, son Gerald, and daughters Mary and Gladys joined him as fellow investigators, technicians, and artisans.
Between 1901 and 1909, their generative theories were built up into a universe of paintings, photography (a new technology), collages, stencils, and essays. Each format addressed the enigmas of coloration and invisibility in different ways.
Thayer was simultaneously producing, witnessing, and documenting the processes of a living being’s assimilation into its habitat.
John Ruskin (1819 – 1900)
Rocks in Unrest
Phoebe Sarah Marks in Hampshire, England, was born on 28 April 1854. She was the third child of a Polish-Jewish watchmaker named Levi Marks, an immigrant from Tsarist Poland; and Alice Theresa Moss, a seamstress. Her father died in 1861, leaving Sarah’s mother with seven children and an eighth expected. Sarah took up some of the responsibility for caring for the younger children.
At the age of nine, Sarah was invited by her aunts, who ran a school in London, to live with her cousins and be educated with them.
In her teens she adopted the name “Hertha” after the heroine of a poem by Algernon Charles Swinburne that criticized organised religion.
By age 16, she was working as a governess, but George Eliot supported Ayrton’s application to Girton College, Cambridge.
Eliot was writing her novel Daniel Deronda at the time. One of the novel’s characters, Mirah, was said to be based on Ayrton.
During her time at Cambridge, Ayrton constructed a sphygmomanometer, led the choral society, founded the Girton fire brigade, and, together with Charlotte Scott, formed a mathematical club. In 1880, Ayrton passed the Mathematical Tripos, but Cambridge did not grant her an academic degree because, at the time, Cambridge gave only certificates and not full degrees to women.
Upon her return to London, Ayrton earned money by teaching and embroidery, ran a club for working girls, and cared for her invalid sister.
She was also active in devising and solving mathematical problems, many of which were published in “Mathematical Questions and Their Solutions” from the Educational Times.
In 1884 Ayrton patented a line-divider, an engineering drawing instrument for dividing a line into any number of equal parts and for enlarging and reducing figures. Its primary use was likely for artists for enlarging and diminishing, but it was also useful to architects and engineers. From then until her death, Hertha registered 26 patents.
That year Ayrton began attending evening classes on electricity at Finsbury Technical College, delivered by Professor William Edward Ayrton, a pioneer in electrical engineering and physics, and a fellow of the Royal Society.
In 1899, she was the first woman ever to read her own paper before the Institution of Electrical Engineers. Her paper was entitled “The Hissing of the Electric Arc”. Shortly thereafter, Ayrton was elected the first female member; the next woman to be admitted to the IEE was in 1958.
She petitioned to present a paper before the Royal Society but was not allowed because of her sex, and “The Mechanism of the Electric Arc” was read by John Perry in her stead in 1901.
Ayrton was also the first woman to win a prize from the Society, the Hughes Medal, awarded to her in 1906 in honour of her research on the motion of ripples in sand and water and her work on the electric arc.
By the late nineteenth century, Ayrton’s work in the field of electrical engineering was recognised more widely. At the International Congress of Women held in London in 1899, she presided over the physical science section, and she spoke at the International Electrical Congress in Paris in 1900. Her success there led the British Association for the Advancement of Science to allow women to serve on general and sectional committees.
Ayrton’s interest in vortices in water and air inspired the Ayrton fan, used in the trenches in the First World War to dispel poison gas.
She helped found the International Federation of University Women in 1919 and the National Union of Scientific Workers in 1920.