A biome is a major ecosystem that extends over a broad region, has a characteristic climate, and presents a typical common appearance due to the suite of organisms that are adapted to it. In the context of a garden world or a large megahab it is a subset of the overall ecosphere, whereas with smaller worlds or habs a biome and its overall ecosystem may be one and the same. The dominant autotrophic organisms (the vegetation or equivalent) tend to converge on a set of common morphotypes adapted to the local pattern of available temperature, moisture, nutrients, energy flux, air or water movement, and so on, so one may see biomes that are similar even if the particular organisms are unrelated. For instance, 'rainforest', 'desert', 'savanna', 'tundra', and 'reef' biomes arose independently at multiple times and in multiple locations on Old Earth, and analogues of these may be seen even on completely non-Terragen garden worlds. Many other biome types are now known that were either long extinct when humans first developed the concept or were completely unknown on Old Earth, either because that particular combination of abiotic factors never existed or because the characteristic organisms that make the biome possible never evolved.
Since biomes are bracketed by a distinct set of abiotic conditions their extent may be primarily horizontal, as with Old Earth's terrestrial biomes, or may have a vertical component, as with Old Earth's aquatic biomes or To'ul'h's aerial biomes. Worlds or habs that are small or have a narrow range of conditions might have only a few biomes. Likewise if the palette of available organisms is small there will be fewer biomes. Worlds lacking the equivalent of multicellular eukaryotic life, where no structure more complicated than a biofilm or a stromatolite exists, may have the same biome over a much broader area, as seen in the case of a very large number of xenobiont worlds. In the case of terrestrial biomes the absence of vascular plants (or the equivalent) means that only a few biomes are seen even in the face of great variety in climate. This may be seen in the case of Old Earth prior to the Devonian, on xenobiont garden worlds like Rajasekhar or Darwin, or in the extensive lichen-plains of any partially terraformed arean world. The 'felts' of New Gaia are an interesting intermediate case. A full-blown evolved garden world like Old Earth, Chorus, Trees, To'ul'h Prime, Ridgewell, or any fully terraformed garden world may have a dozen or more distinct biomes.
The major biomes known to humankind on Old Earth have been widely replicated by humans and other Terragen clades in the time since; variants on them are considered classics of ecosystem design all through the Terragen Sphere. These include:
Old Earth Terrestrial Biomes
Chaparral: regions too dry to support rapid growth in summer and too cool to support it in winter, dominated by heavy scrub adapted to seasonal fire; moderate animal and plant diversity Desert: regions too dry for much of the year to support plant growth; dominated by xerophylic plants including succulents such as cactus or euphorbia; moderate to poor animal and plant diversity Mangrove Swamp: tropical intertidal regions dominated by low-growing salt-tolerant forest; high abundance and moderate diversity of life Midlatitude Forest: cool regions wet enough to support trees but not warm enough to support growth in every season of the year; moderate diversity of plant and animal life Midlatitude Grassland: (steppe/prairie/pampa) cool dry regions covered primarily in grasses and herbs, with some scattered trees; moderate animal and plant diversity Taiga: very cool conditions with sufficient moisture to support conifers; low diversity of plant and animal life Tropical Grassland: warm regions that support plant growth in most but not all seasons of the year, dominated by grasses; high diversity of plant and animal life Tropical Rainforest: warm regions wet enough to support trees that grow in every season of the year; extremely high diversity of plant and animal life Tropical Seasonal Forest: warm regions wet enough to support trees but with a dry season in which growth slows or stops; high diversity of plant and animal life Tundra: very cold regions that do not permit the growth of any plant more than a few inches high due to cold dry winds and frozen soil; dominated by lichens and very low-growing plants Wetland: land covered in shallow water for most or much of the year, dominated by grasslike forms (Pantanal, Sudd, etc.)
Old Earth Marine Biomes
Benthic: sea bottoms below the photic zone; high diversity but low abundance of life Coral Reef: warm shallow regions with high light penetration, based on coral formation; extremely high diversity of life Estuarine: regions where fresh water and sediment enter the marine environment; high abundance and diversity of life Kelp Forest: shallow cool littoral regions rich in macroalgae; high abundance and diversity Littoral:intertidal zones to edge of continental shelf; high abundance and diversity of life Pack Ice: cold regions where ice accumulates on the surface of the ocean for long enough to form a distinct environment Pelagic: ocean surface away from upwellings and in deep water; low abundance and diversity of life; often into regions according to depth (epipelagic, mesopelagic, bathypelagic, abyssopelagic, hadopelagic) or temperature (tropical, temperate, arctic) which may be regarded by some as biomes in their own right Upwelling: regions where nutrient-rich water rises to meet the photic zone; high abundance of life
Old Earth had other biomes in the past that were extinct by the time that baseline humans evolved, either because their characteristic organisms no longer existed or because the conditions that gave rise to them were no longer found in extensive areas of the planet's surface. These included polar gingko forests, rudistid reefs, fern savannas, lepidodendron swamp-forest, epeiric pelagic seas, and so on. These biomes have been reconstructed from lazurogened organisms with varying degrees of authenticity; some of the most extensive reconstructions are in the custody of the Jurassica Institute.
Some xenobiont biomes can often be categorized as variants of the Terragen types. The grasslands of Whisper or the rainforests of Dante are examples of this. Others have no clear analogue on Old Earth. This may be because the prerequisite abiotic conditions are not present or not widespread, as with the saprophytic surface biomes of To'ul'h or else because the necessary evolutionary innovations never arose in Terragen history, as with To'ul'h's cloudforests or Trees' equatorial skywrack forests or Orwell's 'bamboo seas'.
Some Terragen habs have biomes that cannot exist on a planetary surface. This is true of the many varieties of microgravity biomes, or of the rimwall biomes found on Bishop Rings and Banks Orbitals.
Mechosystems may show regions analogous to biomes. Most of these exist by design, since botworlds of Terragen origin have not had time to evolve the complexity that allows something comparable to a biome. However the evolved xeno botworld of Stanislaw has a number of distinct regions that might be called biomes (or mechomes), some with no clear analogue in the biological world.
Biospherics - Text by M. Alan Kazlev The study, design, construction, and maintenance, of artificial biospheres.
Coral Reef - Text by M. Alan Kazlev Aquatic Terragen community of organisms, wave-resistant biological structure resulting from cementation processes and the skeletal construction of hermatypic corals, calcareous algae, and other calcium carbonate-secreting organisms. Forms a rich habitat for many types of marine organisms. Coral reefs are popular in many large Terragen habitats with a strong aquatic component and tropical or semi-tropical climate. Some coral reefs have been provolved to sapience.
Ecological Classification Type - Text by M. Alan Kazlev Typology for a planet or biospheres's ecosystem, the biotic, virchlife, and nanecological counterpart of Planet Classification Type. Also useful in developing biological and mathematical models for preservation, terraforming, colonization, climate control, etc. The system of ecological classifications used today are based upon the classification scheme of the Banks Institute of Ecology (Negentropy Alliance).
Ecopoiesis - Text by M. Alan Kazlev The science and art of designing, shaping, sculpting, or modifying ecosystems.
Ecosystem - Text by M. Alan Kazlev Community of organisms - whether biological or alife - interacting with one another and with the chemical and physical factors making up their environment.
Forest - Text by M. Alan Kazlev Any biome type involving a dense concentration of trees or analogous neogens or xenophyta, distributed over a large area of land. In some biomes, such as rainforest, there are a number of distinct levels, such as canopy and forest floor, each with their distinct micro-ecologies.
Intertidal Zone - Text by M. Alan Kazlev Biome where the sea meets the land, during high tide it is submerged, in low tide exposed to the air. Home to many familiar and unique biological organisms. Many artificial biospheres simulate tides in order to generate intertidal zones.
Littoral Zone - Text by M. Alan Kazlev In a natural or artificial biosphere consisting of both large bodies of water, ample dry land, and natural and/or artificial tides, this is the intertidal zone is where the sea meets the land.