The Infrastructure Beneath Our FeetIn the mist below Turrialba, life beneath the forest floor proves more foundational than stone and steel. Part 3 of Turrialba Volcano and the Infrastructure of Everything.
You can also read this chapter on Notes from the Road. This is part 3 of a 5 part series on how biodiversity underpins human civilization. I am fussing with my reading glasses, which are beading with raindrops and fog. I can barely see Teylor’s headlamp in the distance. “Erik! Come here!” I follow the trail to Teylor, who has stepped uphill into a rocky streambed that intersects the path.
He is ecstatic with his find. A tiny salamander sits on a broad leaf about a foot above the riverbed. It is completely still. Bronze and blue fleck its pinkish body. Its tiny padded feet meld into the leaf’s surface, and it wears a bumpy crown on his forehead. We had just been staring at fungus bursting from a beetle’s body. Now we are staring at a creature that lives because of that same underground architecture. It’s a Ridge-headed Salamander, Bolitoglossa colonnea. Only the second salamander Teylor has ever seen — and the first time either of us has encountered this species. Years ago in the Amazon I found a close relative, Bolitoglossa palmata, and I know this one instantly by the strange geometry of his face. The mouth is wide and slightly skewed, the head flattened and angular, as if shaped to clasp twigs in the dark. When I lean closer, rain dripping off my glasses, he looks uncannily like Nien Nunb, the Star Wars Sullustan who co-piloted the Millennium Falcon during the Battle of Endor. There is something older in that face, too. Not that we descend from salamanders — we don’t — but both of us reach back to the same early experiment in walking. Four-limbed vertebrates pulling themselves from tidal flats, bodies low and slick, learning gravity for the first time. The fact that this is only Teylor’s second salamander says more about Costa Rica than about him. In the Pacific Northwest, if I flip logs in spring or kneel beside a creek, I can usually find one: a flash of orange beneath bark, a coiled body under a stone. Here, it’s different. All forty-four Costa Rican species are lungless. Nearly all live in the trees. They spend their lives in the cloud forest canopy, moving through bromeliads and wet branches far above eye level. To see them regularly you would need ropes, harnesses, and a tent strung a hundred feet up in the mist. Even there in the heights, they breathe through their skin. They depend on moisture. They remain creatures of water.
What unites all land-dwelling salamanders is that they inhabit substrate. They live in matter in transition: soil becoming forest, leaf becoming humus, wood becoming fungus. They dwell where life is being taken apart and reassembled. And beneath that transition lies the meshwork that makes their world possible — the one I had just witnessed a few moments ago. The relentless rain drives water into the soil. A centimeter below this drenched surface, delicate branching filaments of fungus — hyphae — extend from their tips, advancing cell by cell. They lengthen. They branch. They split and rejoin. Each tip softens what lies ahead and bends toward moisture and faint traces of food. They emit tiny electrical flickers that travel through the threads, signals bouncing back and forth through jungle and grassland. Within each filament, liquid flows steadily, sending nutrients through the same underground network. When compatible filaments encounter one another, they pause. Each carries its own genetic signature — a quiet declaration of who it can join with. Some fungal species possess not two sexes, but hundreds or even thousands of mating types. When two suitable threads meet, they recognize one another chemically. Their walls soften. They fuse. Underground, threads find one another. They touch and merge, opening at the seam until their interiors run together. What began as two continues as one, extending outward through the soil. It is quiet choreography in the dark. Rain drums on my umbrella while, beneath my boots, thousands of microscopic courtships unfold. Romance in the mud. What appears to be many threads is often one organism. They move through soil the way rivers move through landscape, following moisture, bending around stone, slipping into hollow twigs. Every tip presses forward into what can be dissolved, borrowed, remade. Below the forest’s spectacle of trunks and leaves, a quieter architecture spreads, filament by filament, contact by contact, stitching substrate into something living and shared. A single gram of forest soil can contain meters of hyphae. Multiply that across an acre and the network becomes continental. Globally, fungal biomass is immense — comparable in scale to the mass of animals. While we count big animals like deer, jaguars, cattle, and ourselves as the visible engineers of landscapes, fungi are building planetary infrastructure in the dark. Can you imagine explaining this in an airport lounge? “Yes, the invisible threads beneath the forest weigh more than all the world’s animals.” Security would escort me out. The largest known mycelium individual, a Honey Fungus, exists back home in Oregon. It stretches three and a half miles wide beneath Malheur National Forest and may be 8,000 years old. One organism. Miles across. Older than most human civilizations.
These threads lace through root tips, wrapping them, entering them, braiding themselves into living tissue. Tree roots don’t stop at their own tips. They braid themselves into fungal threads, trading contact for reach, turning a modest root system into something vastly larger than the plant could manage on its own. The fungi do the wandering. They slip into tight mineral cracks and through softening wood, pulling in phosphorus, nitrogen, zinc, copper — elements trees cannot easily pry loose for themselves. A tree can photosynthesize all day and still come up short on those raw materials. So it pays. Sugars made from sunlight move downward, out of leaves and into soil, feeding the mycelium that forages on its behalf. What looks like separate trunks aboveground is, below the surface, more like an exchange floor — carbon moving one direction, minerals the other, each side dependent on the other’s labor. The network carries warnings. When a leaf is chewed by insects, chemical shifts ripple down into the roots and outward through the fungal web. Neighboring plants adjust before the damage spreads. Leaves toughen. Defenses rise. The message travels underground first. The network does more than pass along warnings. It coordinates growth. It redistributes stress. It shapes who thrives and who merely survives. In grasslands, fungal threads link roots across entire meadows, helping plants share water during drought. In forests, they help decide which seedlings establish and which fail. Some trees funnel carbon generously. Others conserve. The network shifts in response. Sugars move toward the shaded, the stressed, the newly germinated. Nutrients flow along gradients of need. A forest canopy rises from decisions made belowground. What we see in trunks and crowns is the outcome of exchanges carried out in darkness. Hyphae sense changes in moisture, chemistry, and damage. During dry spells, water moves laterally through shared connections. When one plant is attacked, chemical signals spread through the web before leaves show visible harm. The network distributes resources, buffers stress, and absorbs shock. The forest stands because of decisions made between fungal filaments and the trees and plants themselves. Carbon moves through these connections as well. Older trees send excess sugars toward shaded seedlings. In dense forests where young trees might otherwise starve, this quiet redistribution shapes survival. Different species share the same networks. Fir may link to birch, pine to shrub, grasses to wildflowers. What looks separate aboveground becomes, belowground, a living conversation conducted in carbon and mineral. This infrastructure stabilizes soils, regulates nutrient cycles, governs energy flow, and stores carbon. Beneath every field of wheat, every orchard, every city reservoir, the same architecture operates.
Just moments ago, we were looking at a dead beetle, a dismantler of wood. Its mandibles break cellulose into smaller pieces. It does not finish the work alone. When a tree falls, beetles carve their galleries first. Then the mycelium enters the grain. Wood pales and softens. Structure loosens into soil. Carbon chains break. Nutrients free. Forests regrow after fire and hurricane because fungi reduce what came before into accessible form. The planet’s nutrient economy runs on fungal metabolism. What we call soil is, in large part, the proud work of mycelium. For more than 400 million years, fungal filaments have been transacting with plant roots. Before forests, there were fungal threads. Before soil, fungal enzymes softened rock into sand. Animals built ecologies atop substrates fungi had already shaped. When humans began planting grain, we stepped into an ancient partnership. Most of the crops that feed the world — wheat, rice, corn, beans, vegetables — still rely on fungal threads to gather nutrients their roots cannot reach alone. Strip away the fungi, and harvests grow fragile. Nearly every calorie that has sustained agricultural civilization has passed, somewhere along its chain of dependency, through fungal networks. Civilization rests on harvests. Each year plants push enormous amounts of carbon belowground. Not all of it lingers, but fungal networks help trap a portion of that flow, weaving it into soil in forms that do not immediately return to air. When those networks are broken — by plowing, by clearing land, by drenching fields in chemicals — the chemistry shifts. Soil that once held carbon begins releasing it. What should function as a reservoir becomes a leak. The damp earth beneath my boots is not scenery. It is part of the planet’s climate machinery. History has already shown what happens when soil fails. Irrigated fields in ancient Mesopotamia slowly salinized and lost productivity. In the Maya lowlands, forest clearing and erosion turned into decline. When the living fabric beneath a civilization thins, yields falter first. Then stability follows. We have cataloged roughly 150,000 fungal species. Many researchers suspect the real number may be in the millions. Each one occupies a narrow role, tuned to a particular forest, grassland, or wetland. Each influences how nutrients circulate, how soil aggregates, how ecosystems absorb shock. Reduce that diversity and the system does not collapse instantly. It tightens. Its range of response narrows. So what does that tightening mean for the biosphere, and for us? Water that once infiltrated begins to run off, dragging soil with it. Farmers compensate with more fertilizer to coax the same yield from thinner ground. Streams carry heavier sediment loads. Reservoirs silt faster. Forests endure drought with less resilience because roots no longer tap into shared reserves. Carbon that once settled into soil returns more quickly to the atmosphere. Nutrients move faster and leak away. Systems that once buffered disturbance begin to loosen. At first, the shifts resemble inconvenience: declining yields, stressed trees, higher input costs. Over decades, they accumulate into instability. Erosion advances. Margins narrow. Capacity diminishes. Fungal diversity is already thinning. Industrial tillage severs hyphal networks. Fungicides suppress symbiotic partners alongside pathogens. Land conversion fragments underground continuity. Climate shifts alter the moisture regimes fungi depend upon. A complex system is already growing simpler. Already, about ten percent of all land on Earth is used for agriculture, and another thirty percent for grazing and pasturelands. Another two percent is covered in concrete urban zones. And even of the thirty percent that remains forested, much is logged — not truly wild. An enormous percentage of fungal networks are already fragmented, damaged, burdened, or lost. Agriculture grows more brittle. Crops rely increasingly on synthetic nitrogen and phosphorus, inputs derived from fossil fuels and mined reserves that are finite, fundamentally dangerous to our climate, and geopolitically uneven. As natural nutrient exchange declines, fertilizer dependence rises. Costs increase. Runoff intensifies. Downstream dead zones expand. Water systems destabilize. Soils with reduced fungal biomass absorb less precipitation. Floods sharpen. Droughts deepen. Reservoirs accumulate sediment more quickly. Carbon cycles accelerate. Fungal networks move carbon into stable pools of soil. When those pathways thin, carbon lingers less securely underground and returns more readily to the atmosphere. In that way, the health of mycelium networks is one of our defense systems against runaway climate change. When these networks decline, the effects accumulate gradually. Yields decline. Insurance rates rise. Rural economies tighten. Migration pressures build where soil productivity falters. Food insecurity expands outward from vulnerable regions. Last summer, on the islands of Malta and Gozo — where thin soils and water scarcity make agriculture precarious — this same pattern kept revealing itself. A civilization built atop simplified soil systems must work harder and spend more to replace processes that once operated quietly beneath its feet. Each replacement carries cost. Each cost compounds. The question becomes: how much ecological redundancy can be stripped away before the capacity to absorb disturbance narrows beyond recovery? Mycelial networks are not thinning in isolation. Forests are fragmenting. Insects are declining. Soils are eroding. Hydrologic cycles are destabilizing. It is the convergence among all these things that is difficult to grasp. These systems interact across scales, microbial, botanical, atmospheric, in ways that exceed our current capacity to fully model them. Even the atmospheric systems described in IPCC reports, vast as they are, represent only one layer of a far more entangled biospheric architecture. The salamander lifts one forelimb and advances it across the leaf’s midrib. Rain beads along its back and slides away. No vertebrate group is unraveling as quickly as amphibians. Forty percent are now considered at risk of extinction. In the span of my own lifetime — since the years I spent digging in the dirt looking for worms — roughly two hundred species have vanished, some of them the most astonishing in their color and form. One of the chief culprits is chytrid fungus. Humans have ferried it across continents, often without knowing it. The pathogen attacks the skin, the very surface amphibians use to breathe and regulate water. In some places the impact is shockingly swift: populations that once seemed secure crash in a matter of weeks. Their decline registers disturbance moving through the system. They are our siren. Salamanders falter while forests still appear intact. Frogs vanish while watersheds continue to flow. Their collapse tells of the stress lines of the near future. They carry early tremors of deeper instability, faint as the drip of water from the leaves above us. The salamander stares back at us from his perch. Teylor crouches beside me, silent, his headlamp catching the rain. The creek continues its conversation with the rain in the dark. Under this slope lies a living lattice of fungal diversity stabilizing soil, storing carbon, routing nutrients, sustaining forest resilience. Civilization imagines foundations of stone and steel. The real foundation hums beneath leaf litter in filament and exchange. We turn back toward the trail. Beneath us, hyphae extend, fuse, divide, trade carbon, glue soil, and hold the slope that holds the river that feeds the valley that feeds the city. The threads continue negotiating survival. And ours. Part 4 of 5 in two weeks. Notes from the Road is free today. But if you enjoyed this post, you can tell Notes from the Road that their writing is valuable by pledging a future subscription. You won't be charged unless they enable payments.
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