Excerpted from "The Songs of Trees" by David George Haskell, published 2017 by Viking, an imprint of Penguin Publishing Group, a division of Penguin Random House LLC. Copyright by David George Haskell, 2017.

In 1972 the Landsat satellite, a truck-size marvel of New Astrology, was hurled into orbit. No longer would we peer up at shifting patterns of stars to augur the future. We had a star of our own. In 2013 the eighth Landsat satellite was launched, a continuation of the longest-running space-based study of the Earth’s vegetation and terrain. These satellites skate the sky, circling the globe every 100 minutes, recording the scene below with electronic sensors. Like a combine working a wheat field, the path of Landsat’s orbit is arranged in offset swaths to cover the entire field, the globe. By projecting trends from the last decades, we see through a satellite’s glass, darkly, and squint into the future.

Landsat’s images have a resolution of 30 meters; they are painted with a fat-tipped brush. But the forest community is a filigree drawn with the finest pen. To understand the satellite, we have to come back to ground. I’ve returned to the fir tree in summer and, except at night, when the cool air pools and the sound lens returns, the trains and trucks have left the forest. Instead, the wind directs a chorus of trees. Aspen leaves shudder when the air moves slowly, then spasm into pattering chaos in more forceful gusts. A little calmer, drier, are the white birch leaves that lift from tap to fizz as the wind picks up. These deciduous trees almost smother the rustling, chafing sounds of the fir.

The balsam fir tree holds its stiff needles apart. These living bristles are silent, except in the highest winds. But browned, fallen needles caught in the living foliage rub against the thick, dangling shag of horsehair, antler and rosette lichens that drapes every branchlet in the tree. These combs and tangles grate as twigs bob and the main trunk sways. Dead needles and cone scales drop, tik, into the moss below. Higher wind speeds invigorate the abrasion. The tree hisses like fine steel wool burnishing a tabletop, a sound that is strong, corrosive, but with a soft bite.

The first dozen years of the millennium saw 2.3 million square kilometers of forest lost but only 800,000 regrown.

The fir’s summer song is one of dead matter, moss and lichen, seemingly minor parts of the forest network. Our human senses — and therefore our sense of what is important — are tuned to louder creatures, not to the murmurs of fallen needles and dreadlocks of moss or lichen. We deceive ourselves, though, if we don’t occasionally turn from eagles, squirrels and aspen to examine the duff and dross of forests. A study of these recondite members of the community unveils how changing forests connect to global cycles of energy and matter. Landsat’s data finds its meaning in the soils and "lower" creatures of the boreal forest.

Soils in boreal forests hold three times as much carbon as all the forests’ tree trunks, branches, lichens and other aboveground life combined. Roots, microbes and decaying organic matter are therefore a vast repository of carbon. Depending on the details of accounting methods, boreal soils are either the world’s greatest terrestrial carbon store, outweighing even lush tropical forests, or they come a close second. Worldwide, soils contain three times as much carbon as the atmosphere, so the future of our climate depends on the fate of hissing and rasping fir needles. If the carbon encased in these falling needles should turn skyward instead of lodging in soil, our warming blanket of carbon dioxide would turn to a well-stuffed, overheating quilt.

The enormity of the boreal carbon reserve is partly due to the vastness of the forest itself. One-third of the world’s remaining forests grow in the boreal. But even if we ignore their extent, the forests are still disproportionately rich in carbon. When dead needles and mosses lie in cold, water-saturated soils, decomposition is sluggish and a backlog of dead matter soon accumulates. For much of the year, the ground is frozen, paralyzing the microbial activities that turn solid matter into airy carbon dioxide. When summer’s meager and short-lived warmth returns, the microbes are again slowed, this time by sodden, acidic conditions. As I stand at the fir, the hundred iridescent-winged mosquitoes that hold me in a cloud of soft, humming wingbeats attest to these swampy conditions.

Conditions in winter and summer conspire to build soil carbon. Over the thousands of years that have passed since the last ice age, at least 500 petagrams (500 thousand million metric tons) of carbon have accumulated in boreal soils and peatlands. We get a glimpse of this carbon in the gardening aisle of a shopping center: the pallets of "peat moss" stacked to the ceiling are flecks of boreal and arctic carbon, taken from boggy soil, then shipped south.

Landsat’s pictures do not run through the filters of creative accounting. They report a boreal forest in retreat.

The boreal forest is warming much faster than the rest of the globe. Fires have become more frequent, accounting for much of the recent loss of forest. In a fire, not only is carbon in the soil incinerated, but the remnants are left unprotected after flames destroy covering vegetation. As fires release carbon to the atmosphere, the boreal forest turns from a carbon "sink," a place that absorbed and stored carbon, into a carbon "source," a place where the net flow of carbon is from the soil to the atmosphere. Because atmospheric carbon is a greenhouse gas, the conversion of the boreal forest from a carbon sink to a carbon source adds yet more eiderdown to the atmospheric quilt.

Less visible than fires, but potentially just as important, are the changes in the soil’s network of relationships. Warmth sends soil microbes into a frenzy. Their activity increases exponentially as soil temperature increases. If the warming persists for days or weeks, the composition of the community changes, further accelerating activity as cold-adapted microbes are replaced by heat lovers. The result of these changes is faster rot. Dead needles, roots, fungi and microbes are processed through the soil’s living community and their remains sent to the sky. The biological fire makes no smoke, but it is all-pervasive and therefore more important to the global flow of carbon than the drama of flame.

The supply of nitrogen also affects the vigor of decomposition. When nitrogen is limited, microbes slow their work and carbon builds up in the soil. This state of mild nitrogen starvation is the normal condition for microbes in most of the boreal forest. The mantle of lichen and moss that covers every surface in boreal forests intercepts and captures nitrogen from rain and dust, stopping nitrogen from reaching microbes in the soil. But when the lichen and moss communities are gone, after a fire or after herbicide treatments for forestry, nitrogen flows to the soil microbes unhindered and acts like a shot of caffeine for the process of decomposition.

The relationships among roots, fungi and microbes also modulate the effects of nitrogen. In the boreal forest, most tree roots are fused with fungi that specialize in sucking nitrogen from the soil. The trees gain a source of carbon and the fungi are rewarded with sugary gifts from the trees. The microbes living in the soil away from roots, though, lose out. The root/fungus partnership grabs nitrogen that the soil microbes could have used to power their business of rotting the dead. Where such root/fungus partnerships  thrive, microbes are listless and carbon builds up in the soil. The boreal is one such place. Farther south, tree roots associate with different kinds of fungi and they do not draw down the soil’s nitrogen reserves. These southern trees are already moving into the boreal, pushing northward as temperatures rise. If this continues, yet more of the boreal forest’s carbon will move from soil to sky.

Worldwide, soils contain three times as much carbon as the atmosphere, so the future of our climate depends on the fate of hissing and rasping fir needles.

Sitting on the moss and chert under the fir tree, I can sense the forest’s behavior in many ways: through the tap of falling cone scales or the bellow of a train, in the society of roots or the cultural memory of chickadees, and through the remembered abstractions of carbon budgets or Landsat pictures. In all these, I encounter the continuation and elaboration of the Gunflint’s ancient network of living thought. How this thought moves into the future will depend on the relationship among needle, root, microbe, fungus and human.

In the boreal, there is reason to hope that we’ll guide the human part of this relationship with forethought. Over the last two decades, continent-wide planning for conservation, forestry and industry in the boreal forest have brought people together who have fought for years in the law courts. Now timber companies, industry, conservation groups, environmental activists and governments, including those of the First Nations, are talking to one another.

These conversations take many forms, manifesting in agreements, frameworks, initiatives, panels and councils. Such human talk is part of the forest’s larger system of thought, one way that the living network can achieve a measure of coherence: a diffuse conversation, able to listen and to adapt. To date, swaths of boreal forest as big as many countries — hundreds of thousands of square kilometers, more than 10 percent of Canada’s boreal forest — have been mapped for conservation, for carbon-savvy logging, for threatened animals and for sustainable timber production. In some places relationships among parties in the negotiations are strained; as in the rain forest, conflict is part of the network. But perhaps more important than the details of any map or agreement is the multiplication of connections among people. The boreal forest can now benefit from the diversity of experience within the human community and, through this, our varied ways of understanding the ecology of the world.