Growing Trees by Mimicry:
Replicating Forest Conditions in the Urban Landscape
September 15, 2026
Trees are always foresting!
And they're good at it—they've been foresting in concert with a vast network of organisms for over 350 million years, surviving four mass extinction events!
During each extinction event, the planet saw enormous temperature swings and large-scale nutrient starvation of any organism that existed entirely above ground. Trees used their insulated underground store of nutrients to rejuvenate each time. And that same plan for evading the planet's most dynamic shifts can be used to preserve the trees of our landscape in the face of small stressors and an ever-changing climate.
If we were to plant a quaking aspen or ponderosa pine in the middle of a field, success would be a forest. Whether through wind-blown seeds or clonal roots, the end result is always the same—a forest.
The Original Forest Blueprint
Trees shade the ground around them as we rotate in relation to the sun. They release nutrients back into the soil each year by shedding roots, leaves, twigs, branches, bark, flowers, and seeds. This cycle keeps soils cool, moist, and ready to host a new generation of saplings.
As this litter and duff decomposes, it enriches the soil and supports life from microscopic fungal hyphae to apex predators who feed on forest floor inhabitants. Even when trees fall, their bodies become nurse logs for new life to germinate.
Trees are investors, caretakers, and community generators. Trees have a record of resilience and longevity nearly unrivaled by Earthly standards.
The urban forest is an entirely new landscape for trees with unique stressors. If we wish to protect our investment and grow trees for the next generations, we should replicate forest conditions in the urban landscape.
Trees are always foresting!
And they're good at it—they've been foresting in concert with a vast network of organisms for over 350 million years, surviving four mass extinction events!
During each extinction event, the planet saw enormous temperature swings and large-scale nutrient starvation of any organism that existed entirely above ground. Trees used their insulated underground store of nutrients to rejuvenate each time. And that same plan for evading the planet's most dynamic shifts can be used to preserve the trees of our landscape in the face of small stressors and an ever-changing climate.
If we were to plant a quaking aspen or ponderosa pine in the middle of a field, success would be a forest. Whether through wind-blown seeds or clonal roots, the end result is always the same—a forest.
The Original Forest Blueprint
Trees shade the ground around them as we rotate in relation to the sun. They release nutrients back into the soil each year by shedding roots, leaves, twigs, branches, bark, flowers, and seeds. This cycle keeps soils cool, moist, and ready to host a new generation of saplings.
As this litter and duff decomposes, it enriches the soil and supports life from microscopic fungal hyphae to apex predators who feed on forest floor inhabitants. Even when trees fall, their bodies become nurse logs for new life to germinate.
Trees are investors, caretakers, and community generators. Trees have a record of resilience and longevity nearly unrivaled by Earthly standards.
The urban forest is an entirely new landscape for trees with unique stressors. If we wish to protect our investment and grow trees for the next generations, we should replicate forest conditions in the urban landscape.
Let's look at this in a little more detail.
Trees as Water Columns
Trees are ~80% water by mass. If you lifted a 100-pound section of living tree, roughly 80 pounds of what you would be holding would be water. A living tree is essentially a giant, rigid column of water held together by a thin carbon skeleton. To stay upright, to transport nutrients to all of its living tissues, and conduct all of its metabolic processes, a tree requires a steady supply of water. Trees have adapted to translocate water against gravity, utilizing cellular diffusion like pumps and vacuums to maintain turgidity.
All of this STEM work (pun intended) takes time.
To do this—to tree—they need to root in a medium that can absorb and mobilize both water and nutrients. So they made it. You read that right: trees made soil. They've since covered the majority of Earth's land mass with fertile, water-retentive topsoil. We owe our very survival to this engineered medium.
Forest Soils: Engineered by Trees
Forest soils are a mix of organic matter and inorganic minerals, cohesive enough to root and stabilize a massive redwood but porous enough to mobilize hundreds of gallons of water to that same tree each day.
This perfect medium is built through the work of perpetual shedding and decomposition!
Decomposition is a process of hunting, feeding, and excreting by a community of organisms. Earthworms and ants tunneling, nematodes ingesting, hyphae absorbing—all of this activity results in soil pore space. A forest soil is ~50% void space by volume, a series of tunnels and pockets suspended by a sticky matrix of decaying detritus and minerals. By contrast, a landscape soil is ~2% void space by volume.
Forest soils are designed with a network of pore spaces to hold water and nutrients. Forest soils are dynamic—constantly moving and changing.
The rate in which water infiltrates soil, absorbs nutrients, and moves to the tree is the greatest determinant of tree health, rate of growth, and tree longevity.
Trees as Water Columns
Trees are ~80% water by mass. If you lifted a 100-pound section of living tree, roughly 80 pounds of what you would be holding would be water. A living tree is essentially a giant, rigid column of water held together by a thin carbon skeleton. To stay upright, to transport nutrients to all of its living tissues, and conduct all of its metabolic processes, a tree requires a steady supply of water. Trees have adapted to translocate water against gravity, utilizing cellular diffusion like pumps and vacuums to maintain turgidity.
All of this STEM work (pun intended) takes time.
To do this—to tree—they need to root in a medium that can absorb and mobilize both water and nutrients. So they made it. You read that right: trees made soil. They've since covered the majority of Earth's land mass with fertile, water-retentive topsoil. We owe our very survival to this engineered medium.
Forest Soils: Engineered by Trees
Forest soils are a mix of organic matter and inorganic minerals, cohesive enough to root and stabilize a massive redwood but porous enough to mobilize hundreds of gallons of water to that same tree each day.
This perfect medium is built through the work of perpetual shedding and decomposition!
Decomposition is a process of hunting, feeding, and excreting by a community of organisms. Earthworms and ants tunneling, nematodes ingesting, hyphae absorbing—all of this activity results in soil pore space. A forest soil is ~50% void space by volume, a series of tunnels and pockets suspended by a sticky matrix of decaying detritus and minerals. By contrast, a landscape soil is ~2% void space by volume.
Forest soils are designed with a network of pore spaces to hold water and nutrients. Forest soils are dynamic—constantly moving and changing.
The rate in which water infiltrates soil, absorbs nutrients, and moves to the tree is the greatest determinant of tree health, rate of growth, and tree longevity.
Urban Soils & The Compaction Problem
Urban soils have a high soil bulk density because we engineer them that way. We purposely select clayey-sand mixes to minimize micro and macro pore space, then we compact it with heavy machinery. We do this so our homes and roads don't shift—a wise conservation effort.
Urban soils absorb less water by design, remaining relatively static—less swelling and contraction. And over time, urban soils generally remain compacted due to cultural practice.
Urban soils see far more machinery and foot traffic. Traffic is a persistent contributor to compaction. Next time you're out traveling a popular forest trail, examine the trail's density underfoot and then step off into a wooded area. You don't need any special tools to see that traffic results in compaction.
However, the single largest contributor to soil compaction in the urban setting is our habit of sanitizing our landscapes. We typically remove anything that sheds, preserving no semblance of a tree's desired medium within our trees' root zones. We pick up branches after windstorms; we rake or suck up every leaf. I've had clients apologize for not cleaning up under their trees before my arrival.
We typically like things clean, tidy, and under control.
Urban soils have a high soil bulk density because we engineer them that way. We purposely select clayey-sand mixes to minimize micro and macro pore space, then we compact it with heavy machinery. We do this so our homes and roads don't shift—a wise conservation effort.
Urban soils absorb less water by design, remaining relatively static—less swelling and contraction. And over time, urban soils generally remain compacted due to cultural practice.
Urban soils see far more machinery and foot traffic. Traffic is a persistent contributor to compaction. Next time you're out traveling a popular forest trail, examine the trail's density underfoot and then step off into a wooded area. You don't need any special tools to see that traffic results in compaction.
However, the single largest contributor to soil compaction in the urban setting is our habit of sanitizing our landscapes. We typically remove anything that sheds, preserving no semblance of a tree's desired medium within our trees' root zones. We pick up branches after windstorms; we rake or suck up every leaf. I've had clients apologize for not cleaning up under their trees before my arrival.
We typically like things clean, tidy, and under control.
Resource Sheltering: The Canopy Effect
Let's look at one more aspect of a forest—resource sheltering. If you walk inside a dense forest on a windy day, you may hear and see treetops blowing, the creaking and squeaking of crowns, and perhaps the thwapping of cones hitting the ground. But you're unlikely to feel much wind on your face. Forests act like giant airplane wings, foiling wind around them as a unit.
And perhaps you've been in such a successfully dense forest that the occasional gleams of sunlight piercing through the canopy were absolutely blinding. Forests do a remarkable job of sheltering their soil from agents of desiccation, like wind and sun. Beneath the canopy and duff, some parts of a forest floor never see sunlight and are rarely touched by wind.
So if we're saying that a 350-million-year run is a marker of success—and we are—we should be mimicking or simply allowing their behaviors in our landscape.
Forest soil holds more water and nutrients, moves water faster, and is generously sheltered by its own processes. This has resulted in a self-sustaining system that can persist for hundreds of millions of years and withstand multiple mass extinction events.
Let's look at one more aspect of a forest—resource sheltering. If you walk inside a dense forest on a windy day, you may hear and see treetops blowing, the creaking and squeaking of crowns, and perhaps the thwapping of cones hitting the ground. But you're unlikely to feel much wind on your face. Forests act like giant airplane wings, foiling wind around them as a unit.
And perhaps you've been in such a successfully dense forest that the occasional gleams of sunlight piercing through the canopy were absolutely blinding. Forests do a remarkable job of sheltering their soil from agents of desiccation, like wind and sun. Beneath the canopy and duff, some parts of a forest floor never see sunlight and are rarely touched by wind.
So if we're saying that a 350-million-year run is a marker of success—and we are—we should be mimicking or simply allowing their behaviors in our landscape.
Forest soil holds more water and nutrients, moves water faster, and is generously sheltered by its own processes. This has resulted in a self-sustaining system that can persist for hundreds of millions of years and withstand multiple mass extinction events.
Working With 350 Million Years of Success: How do we mimic this?
1. Leave the Leaves - Every year, your tree drops a fresh supply of tailor-made organic matter onto the soil. Did you know this stuff retails for ~$100 a cubic yard at the nursery? Instead of bagging what your tree sheds, leave it in place or rake it into the beds beneath the canopy. If you have your trees pruned, ask your arborist to leave the clean wood chips behind for free mulch.
2. Protect the Root Zone - Minimize heavy foot traffic, lawn equipment, and parking beneath the tree’s outer branches. Simply giving the ground a rest from weight protects the precious soil pore space your tree relies on to breathe.
3. Water Deep, Then Let It Dry - Allowing the soil beneath a tree to dry out between waterings ensures that the water filling the pore space has been absorbed, opening the soil back up for oxygen. Keeping soil constantly saturated locks water and nutrients in place, starving the roots of air and preventing efficient uptake.
4. Ditch the Fabrics and Weed Barriers - Soil needs to breathe! Tree roots require a continuous exchange of oxygen and water to survive. Non-breathable weed barriers and plastic tarps restrict gas exchange and water penetration, creating stressful, suffocating conditions underground. If removing the entire barrier isn't practical, cutting it back several feet away from the tree's trunk flare makes a huge difference.
1. Leave the Leaves - Every year, your tree drops a fresh supply of tailor-made organic matter onto the soil. Did you know this stuff retails for ~$100 a cubic yard at the nursery? Instead of bagging what your tree sheds, leave it in place or rake it into the beds beneath the canopy. If you have your trees pruned, ask your arborist to leave the clean wood chips behind for free mulch.
2. Protect the Root Zone - Minimize heavy foot traffic, lawn equipment, and parking beneath the tree’s outer branches. Simply giving the ground a rest from weight protects the precious soil pore space your tree relies on to breathe.
3. Water Deep, Then Let It Dry - Allowing the soil beneath a tree to dry out between waterings ensures that the water filling the pore space has been absorbed, opening the soil back up for oxygen. Keeping soil constantly saturated locks water and nutrients in place, starving the roots of air and preventing efficient uptake.
4. Ditch the Fabrics and Weed Barriers - Soil needs to breathe! Tree roots require a continuous exchange of oxygen and water to survive. Non-breathable weed barriers and plastic tarps restrict gas exchange and water penetration, creating stressful, suffocating conditions underground. If removing the entire barrier isn't practical, cutting it back several feet away from the tree's trunk flare makes a huge difference.
Trees don't need us to invent new, complicated systems to keep them thriving—they already engineered the ultimate blueprint hundreds of millions of years ago.
By making a few small adjustments—leaving the leaf litter where it falls, giving the root zone a break from heavy weight, watering deeply, and letting the ground breathe—we stop fighting their biology.
When we give trees room to "forest" in our yards, we protect our property investment and build a resilient landscape that will thrive for generations to come.
By making a few small adjustments—leaving the leaf litter where it falls, giving the root zone a break from heavy weight, watering deeply, and letting the ground breathe—we stop fighting their biology.
When we give trees room to "forest" in our yards, we protect our property investment and build a resilient landscape that will thrive for generations to come.
