In this post we’ll discuss worldbuilding tropical rainforests, where rainforests can be found across an earth-like planet, and how to create some interesting flora and fauna to populate their ecosystems.  

Hey everyone, my name is Matthew, at least at this level of humidity, and this video is part of a series where I will be going through a science-adjacent worldbuilding process step-by-step. Last time we established the foundations for the tree of life on our fictional world of Locus, detailing all the groups of flora and fauna that we’ll be using moving forward. If you missed that video the link should be… here.

For today’s discussion, we’re going to be zooming in on the tropical rainforest biomes, discussing not only how rainforests are classified but also looking at their geography and ecosystems, establishing which flora and fauna are important to rainforests before detailing how to create some fictional organisms of our own.

Tropical rainforests, according to the Koppen Climate Classification system, are classified as areas in which there is no dry season, with all months having average precipitation values of at least 60mm, and temperatures and humidity being similar all year round. Rainforests are distinguished by a closed and continuous canopy, with much of the vegetation being moisture dependent, and the conditions here are simply too wet for regular wildfires.

On earth-like planets, tropical rainforest spread is heavily dependent on surface temperatures and winds. When people think of the equator, they usually think of hot deserts, but providing the temperature doesn’t get too hot, then the equator is actually dominated by lush tropical rainforests. As evaporation from the oceans occurs, the water vapour in the atmosphere increases, which is called humidity. It is this humidity that rainforests thrive in. Across the equator, the intertropical convergence zone is a low-pressure zone with very little wind, allowing for water vapour to settle and not be blown away. Therefore, it is most common for tropical rainforests to occur within the equatorial zones, giving them the very creative name of ‘equatorial climates’. Tropical rainforests that occur outside of the intertropical convergence zone are referred to as ‘tropical trade-wind rainforests’, and are much rarer, due to the wind affecting the humidity levels.

If your planet is like earth, with similar winds and surface temperatures, then you can place your tropical rainforests along the intertropical convergence zone, reaching 10 degrees north and south in continental interiors, slowly tapering off as they reach towards the coasts. Which would look something like… this. If your planet is cooler than earth like our fictional world of Locus is, then less evaporation occurs which decreases overall humidity, making tropical rainforests less extensive, shrinking further towards the equator. Locus’ average surface temperature is around 10 degrees Celsius, and its tropical rainforest coverage will look more like… this. If your planet is warmer than modern earth, then things start to get a little whacky. If the average surface temperature is only a little warmer than earth, then there will be a reduction in overall tropical rainforest coverage, due to it simply being too hot on the equator for many trees to survive. If average surface temperatures are way higher than modern earth though, sitting around 5-10 degrees Celsius warmer, then tropical rainforests would start to form around other low-pressure low-wind zones, which if your wind patterns are the same as earth, occur at the polar fronts. This might sound ridiculous, but it’s actually reasonably well established that Antarctica was once host to extensive rainforests, back when earth was much warmer. On a really hot planet like this, there’d be little to no equatorial rainforests, but instead you might have polar rainforests.

For Locus however, we know that it’s atmosphere, rotation, and wind zones are similar to earth, and that its temperature is slightly cooler, so this is the rainforest coverage that we’ll be going with.

FLORA

For any earth-like planet supporting life, rainforests are easily the greatest source of biodiversity, with around 60% of all organisms calling rainforests their home. In fact, there is such a high level of biomass that ecologists separate rainforests into four distinct layers: the forest floor, the understory, the canopy, and the emergent layer, each with their own ecosystems and unique flora and fauna. Let’s discuss some of the iconic and keystone species that are important to earth’s rainforests and create some of our own for Locus.

Perhaps most importantly, rainforests require trees that will make up… well, the forest itself. Specifically, rainforest trees have to create a dense canopy that blocks sunlight from reaching the lower layers. The most common rainforest trees on earth are an Amazonian palm tree called Euterpe Precatoria, with a tall slender trunk that branches out into fan-like leaves at the very top of the tree. For Locus let’s create two similar trees, the Cutivex and the Crassina, with both clustering most of their leaves at the top of their trunk, branching upwards and outwards, allowing them to reach the emergent layer and sunlight more easily.

As the rainforest is filled with these trees at various growth stages, Cutivex and Crassina are present and important at all levels of the rainforest. Both species are Phorophytes, which refers to a type of tree that are the habitat for other flora that grow on them, rather than with roots into the ground.

Organisms that grow on Phorophytes are called Epiphytes, and the relationship between the two is referred to as Commensalism, which is a type of symbiosis where one species gains benefits, while the other is neither benefitted nor harmed. Non-tree flora present within the understory layer would almost exclusively be Epiphytes, growing off Cutivex and Crassina for support.

The understory has more sunlight present than the forest floor, and is exceptionally humid and warm, creating a perfect environment for flora to thrive. Many species develop beautifully coloured flowers and fruits, and the understory would be a visually vibrant ecosystem. Many plants and flowers that most people are familiar with from houseplants to garden plants are native to the understory of tropical rainforests, including the well-known philodendrons, gardenias, and holly plants. Edible fruits and other vegetation are also common among the understory, including but not limited to cacao beans, bananas, figs, avocados, and acai berries. Many citrus fruits also trace their origins back to the tropical rainforests. If you’re wanting to worldbuild any kind of unique and striking flowers or nutritious fruits, here is the place to do so.

On Locus, the Cutivex we created earlier produce a vividly coloured cyan blue fruit called Cuti Berries that are high in sugar content, while the Crassina trees produce powerfully smelling nuts simply called Crass that are rich in micronutrients, each encouraging creatures to eat them which in turn helps with their pollination process. By offering different nutritional values, the two trees can share pollinators, reducing their competition with each other.

Also standing out among the rainforest flora is the star shaped crimson coloured Ignistella, which utilise a fictional process of energy synthesis to generate their own energy. Here’s a link to the video for more information on how it works. The Ignistella converts any excess generated energy into heat, which gather within its flowers that have evolved to be resistant to high temperatures and protect Ignistella from being eaten, effectively burning any creature that tries to touch them. As it reaches maturity, it’s built-up energy and heat reach a pinnacle, which causes the flowers to ignite small spot-fires, and eventually burst into flame entirely. This flame then triggers seed release from the Ignistella, making it necessary for the organism to reproduce. Within the rainforest, the highly damp environment prevents the fire from spreading, and often combustion events only last a few seconds, which is not enough to destroy the heat resistant flowers. Taken out of its regular humid environment however, Ignistella can easily ignite and stay lit, which unsurprisingly kills the plant.

So, we’ve looked at the tall trees and colourful humid understory, but what about the rainforest floor? While most photosynthetic flora don’t have access to enough sunlight to thrive here, fungi can be found across the rainforest floors in abundance, feeding on the decomposing matter than litters the floor from above.

On Locus, the analogues to fungi are the pileum, and though many different types are abundant among the rainforests, it is the Mortevello that is perhaps the most interesting. As members of the Corpus phyla, they are pileum that have evolved to feed on decomposing flesh rather than vegetation.

Mortevello has also evolved a unique method of reproduction; it has become a parasite that hijacks the motor functions of deceased creatures, functionally reanimating them after they have died. These reanimated dead have very little semblance of their previous cognition, and infected corpses can only use basic jerky movements, becoming hyper-aggressive and having their mouths loaded with Mortevello spores, spreading them to other creatures through bites. Infected bodies are slowly eaten by Mortevello and living creatures that are infected will slowly die as they are eaten alive. Once deceased, Mortevello takes over and can continue to animate a corpse until only bones remain. Outbreaks of Mortevello can completely decimate an ecosystem, though at some point infected creatures may be unsuccessful in spreading their spores, and the outbreak fizzles out.

FAUNA

With the sheer amount of biodiversity present, it’s possible to worldbuild effectively any type of creature you’d like, and there aren’t too many constraints besides ensuring that the creatures can survive in hot and humid conditions. On earth, some iconic rainforest inhabitants include the ferocious jaguars, the curious lemurs, and the tree-dwelling snakes and frogs. In earth’s history, tropical rainforests were also heavily dominated by a wide variety of dinosaurs, which were well adapted to life on a much hotter, more humid earth.

On Locus, the two main classes for larger creatures are Frigidi and Calidi, and the Calidi are furred creatures, and so are probably not well suited for life among the tropics. This means the tropical rainforests would be dominated by the cold blooded scaley Frigidi, among which their orders are directly inspired by lizards, including dinosaurs and crocodiles, and so we can draw from a lot of existing inspiration to make our fictional rainforest dwellers.

Magnamaw are a family of hypercarnivores that are rulers of the rainforest, with colossal body sizes and terrifying bite forces that rival those of saltwater crocodiles and the largest carnivorous dinosaurs. Some individual species are more amphibious than others, but across the board all Magnamaw lay their eggs in water. They are, unsurprisingly, apex predators, and due to their incredible sizes, they are mostly solo creatures, with territory that is so extensive that very few would exist across the planet. Like most Frigidi, females are larger than males, and they almost always accept mating advances from males, though often turn on them after mating, making their encounters dangerous, almost always violent, and occasionally fatal.

The next important creature we’ll discuss are the Visec, the largest Planapede across the entire planet, which are analogous to insects. This chitinous creature moves in a slithering motion across the rainforest floor, with rows of small legs underneath its body, similar to a millipede. Despite their literally creepy appearance, Visec are herbivorous, with its diet mostly consisting of Pilea, supplemented with whatever Folia it can reach from the forest floor. As they shuffle across the forest floor, they clear paths that are clearly visible throughout the rainforest, that are then used by a wide variety of other creatures for navigation. In addition, whilst their reproductive and behavioural patterns are not particularly extraordinary, Visec are responsible for consuming and dispersing many of the rainforest’s seeds. These important ecological roles therefore make the Visec keystone species, and the many other species present within the rainforests of Locus are dependent on the Visec to keep their habitat alive.

Finally among the notable creatures of the tropical rainforests are the Nota, a family within the Aborascensus order. If it isn’t abundantly clear why their family is called the ‘familiar’ family, then hello non-human viewer, it’s a pleasure to meet you! The Nota live among the upper understory and canopy and consider both as their territory. They’re one of the few types of Calidi that thrive within the tropics and have evolved far thinner fur to compensate. They are also nocturnal, sleeping during the day when it is warmest, and are active at night when temperatures drop. Nota live in communities of up to 50 individuals, with both an alpha male and female leading the community. Males collectively hunt prey that they return to their communities, while females gather and stockpile fruit and nuts to be distributed.

If you ARE a human viewer, then it will be unsurprising to you that the Nota are one of the first creatures across Locus to utilise tools in their day-to-day life. They also clasp their hands together in a prayer-like motion as a form of social greeting and sign of non-violence, similar to how humans smile and nod at each other. This is just one of many forms of communication that Nota use, with others including complex vocalisations and calls, hand signals, and grooming. Therefore, predictably, Nota is one of the more intelligent creatures across the planet, and we’ll certainly be bearing them in mind when we establish which creatures are going to evolve to develop civilisations of their own.

So, to recap, rainforests are equatorial climates that are possible due to the exceptional humidity that exists within the intertropical convergence zone. We placed where the tropical rainforests will be located on our map and determined some of the integral flora within the region, designing some of our own fictional equivalents, before also creating some iconic and keystone creatures to inhabit the region.

Join me next time where we’ll move poleward from the tropical rainforests to talk about the savanna biomes. And until next time… stay awesome!