Forest canopies can grow extremely thick and lush, sometimes even enough to support entire villages, but they're not generally enough so as to be entirely separate from the world below them — the creatures living in them are usually at least within viewing distance of the ground, and simply live a ways above it rather than being entirely separate from it. Some settings, though, play host to forests so thick and trees so huge that their inhabitants may go their entire lives without ever seeing, much less setting foot on, anything below the tree canopy.
The disproportionate tree growth may be explained as a result of the setting being extremely fertile and lush, or as due to unusual native plant life. In some cases, it may take place in the canopy of a World Tree. Alternatively, the trees may be entirely regular-sized and the people living in them very, very small.
In extreme cases, this may effectively become a Layered World. Stories set in such settings typically begin in the canopy, portrayed as a sunlit surface world. Beneath it will be any number of strata of understory, leading to a ground layer serving as a dark, shadowy underworld, cut off from the sun and often filled with dangerous creatures. In many cases, the people living in the treetops will view the forest floor with fear and dread, and may be so far removed from it that they may treat things like soil, stones and the surface itself as exotic or even mythical concepts.
In certain cases, it may also be noted that certain resources one needs to get to or below the ground for, like stone and metal, will by necessity be very rare. These may become very valuable as a result of their scarcity, unless the locals have some creative means of getting them.
When settlements are built in such settings, they'll typically have to be Tree Top Towns by necessity.
- Magic: The Gathering:
- The Skyshroud was an immense mangrove forest floating over the waters of a small sea on the plane of Rath. The forest reached immense heights, enough so that the elves living within its canopy could go their entire lives without approaching its root system — a good thing too, as the merrows living in the flooded maze of roots beneath the forest proper were quite hostile to them.
- Murasa, one of the continents of the plane of Zendikar, is covered by thick canopies of vegetation so large that regular-sized forests can grow on their branches. These trees cover the continent so deeply in places that Murasans can go their whole lives without ever setting foot on the ground.
- Pyrulea is a plane in the shape of a hollow sphere around a central star, with its inner surface entirely covered by towering rainforests of trees so huge that their individual leaves are large enough to build a small house on.
- The Death Gate Cycle: Pryan, the world of fire, is a hollow sphere where intense humidity, constant rains, and the light and heat from the four suns at its center have caused its inner surface to become covered in miles-high jungles. The trees' branches support moss plains as large as countries and thick enough to bear the weight of regular-sized forests and small seas, while the forest floor is a lightless underworld of pillar-like trunks leading down to the mazelike tunnels of the humus layer. The elves and humans live in the canopies and on the moss plains, respectively, so far above the ground that stones are rare enough to serve as currency, while the dwarves dig their cities into the trunks of the trees much deeper down.
- Hothouse: In the distant future, after the Earth has become tidally locked with the Sun, millions of years of intense humidity and heat have allowed plant life to completely dominate the world. The greatest of all these plants is a single, titanic banyan fig that covers the entire dayside surface of the Earth, forming an immense three-dimensional jungle. Scattered human tribes live at various levels within the volume of the canopy, avoiding the dangers of the dark, rot-shrouded Floor and the sunlit Tips where the most active predators flourish, alongside hardy eusocial insects and an endless variety of carnivorous plants.
- Humanx Commonwealth: Midworld, which also doubles as a Death World. The entire planet is one gigantic forest so thick no one has successfully penetrated to the planet's actual surface. The only civilizations is a tribe of humans descended from a group of colonists who got stranded there and an illegal pharmaceutical research lab on the other side of the planet.
- Star Wars: The Wookiee homeworld, Kashyyyk, is covered in global forests of kilometers-tall wroshyr trees — according to Star Wars Legends, this is due to it having been mid-terraforming when the responsible Precursor empire collapsed, leaving their machines running for millennia before they eventually ran down. It's traditionally divided into seven layers, counting from the top, and the forest becomes increasingly dangerous and home to progressively nastier beasts the deeper one goes. The Wookiees live in cities built in the branches of the first layer, and going down two or three for a hunt is a rite of passage for young Wookiees; almost nobody ever ventures to the fourth. The seventh layer, consisting of the planet's actual ground, is a lightless, swampy shadowland haunted by ferocious predators — only in stories has anyone made it to the bottom and come out alive.
- Titan's Forest: The world is covered in a forest of titanic trees so large that an entire civilization exists on the branches of its upper canopy, living in cities carved within the great trees' trunks. A magical barrier separates Canopy from Understorey, a world of pillar-like trunks where little light penetrates, home to scattered pale-skinned people who live and die without ever seeing the sun and to ferocious monsters. The dark, mud-encrusted Floor at the very bottom is a thing half of myth for the natives of the Canopy. Almost everything is made up of wood, leaves and tree byproducts by necessity, and stone and metal are rare and precious commodities — metal is mostly available from a single magic tree that draws it up through its roots and deposits it in its fruits.
- Toby Alone: Apart from the time where Toby lives alongside the Grass people, the entire story is set in a single oak tree home to a civilization of minuscule people. However, Sim, Toby's father, hypothesizes that other trees exist.
- Extraterrestrial (2005): The dense atmosphere and low gravity of the blue moon allow its plant life to reach immense heights, and the dominant plants have found methods to extend their reach even further — balloon plants, for instance, support themselves with sacs of buoyant gas, while the pagoda trees grow large bowls to catch rainwater (they're much too tall to draw water purely from the ground) and tangle their branches into a tight mesh to support each other's massive weights. As a result, the trees of the moon reach over a kilometer in height, and almost all of the fauna in the episode consists of flying or arboreal animals living within and above the forests' roof-like canopy; further down, among the pillar-like trunks, almost no sunlight penetrates, and the ground is a lightless world of luminescent scavengers feeding on detritus falling from above.
- Mechanical Dream: The world of Kainas is for the most part covered by Kioux tree upwards of fifteen miles tall, and almost all of civilization lives in cities built amongst their branches. The trees, besides providing most of the resources needed by the setting's species — mostly wood-based by necessity; iron and steel are very rare, high end materials — also act as a buffer against the titan-sized predators that roam the world.
- World Tree RPG: The entire civilization is built in the highest reaches of a single, mind-bogglingly large tree floating in space. The ecosystem there is friendly and well-suited to intelligent beings; lower reaches are progressively less explored and more perilous until the lower trunks become a full-on Death World. Cities are mostly strung out along the upper surfaces of branches — the sides of branches and the trunk, called the Verticals, are mostly home to flying monsters — and metal and stone are very scarce and mostly obtained from certain plants that deposit them in their leaves and fruit.
- Ryzom: Atys, the planet on which the game is set, is a literal World Tree large enough for an entire planet to have accreted on its canopy. The setting's races mostly live on the masses of rocks and earth held up by Atys's branches, with further boughs crossing through the sky and a maze of root networks beneath the crust.
- Orion's Arm:
- Trees is a life-bearing alien planet best-known for its forests of skywrack trees, which can reach a kilometer in height. Some thought is put into how such large plants would operate — Trees' gravity is lower than Earth's to begin with, and the trees grow gas-filled bladders on their upper branches to further support their weights; high humidity is also needed to keep the plants alive, and as it's extremely difficult to pump water above a couple hundred meters in height the trees grow basins with which to catch rainfall to water their upper reaches. The skywracks' immense height has resulted in the creation of multiple canopy layers with distinct ecologies, including a thickly overgrown ground level where almost no light is present and living creatures depend on organic detritus falling from above. The planet was settled by humans modified for a brachiating lifestyle, who live in the upper canopies and make their homes in the trees' hollowed-out seedpods.
- Akilaspecs are genetically engineered trees resembling colossal banyans capable of theoretically infinite horizontal spreadnote and up to five kilometers of vertical growth. Because, again, they cannot pump water vertically for more than a certain distance, they rely on massive bowl-shaped leaves to catch rain and are thus limited in height to the ceiling for raincloud formation. They're designed to serve as living areas and often engineered to grow several structures useful for this role, such as hollows in their limbs that collect water to form lakes, a great variety of edible fruit-like growths, projecting platforms to serve as landing pads and recreation areas, hollow spaces in their trunks and branches where people live, and bioluminescent growths to light these areas. They are often created and inhabited by shepbras, a clade of Uplifted geckos.
- Dyson Trees are genetically engineered plants that can survive in vacuum and synthesize nutrients from comets or icy asteroids, into which they're rooted. They can grow into vast orbital habitats, forming miniature worlds floating in deep space. Inside their trunks and larger branches there are sealed hollows filled with air, inside which other lifeforms — like humans — can live, while their spherical canopies support further air- and water-filled habitats, as well as space-adapted lifeforms.