How could mushroom/fungi forests be possible?

Question

I am currently working on a setting which is fantasy but based around a soft approach to speculative biology.

It is a tidally locked world with the habitable region based around the terminator between the bright hot sun side and the freezing dark, filled with terran descended flora/fauna. The main continent is bisected by a long range of extremely tall volcanic mountains. The south, where sunlight is more plentiful, is relatively similar to terran plant life. But the north, where it goes from twilight to darkness, is where things become much more alien.

One of the ecosystems I want to use are forests of fungal plants in place of trees, located near the ocean in a vague analogue to Europe. My biology isn't the best but I know fungi feed off dead matter.

My question isn't if it could work, but rather how it could work. I was thinking an underground system of dead matter running off into the ocean that the fungi reach down to consume. Also possible there are lots of megafauna which migrate across the continent to pass away in these area, feeding the forest as they decompose.

This setting is fantasy so 100% plausibility isn't necessary (think Dougal Dixon or Flight of Dragons).

Answer 1

Before vascular land plants, there were weird fungal “trees.” People still do not really understand what exactly they were or what they ate. They were called prototaxites.

from pinimg.com

Wikpedia: Prototaxites

Prototaxites is a genus of terrestrial fossil organisms dating from the Late Silurian until the Late Devonian periods, approximately 420 to 370 million years ago. Prototaxites formed large trunk-like structures up to 1 metre (3 ft) wide, reaching 8 metres (26 ft) in height, made up of interwoven tubes around 50 micrometres (0.0020 in) in diameter. Whilst traditionally very difficult to assign to an extant group of organisms, current opinion suggests a fungal placement for the genus. Recent discovery of what are likely algal symbionts makes it a lichen, rather than a fungus in the strict sense.

from livescience.com: Prehistoric Mystery Organism a Humongous Fungus

On the inside, Prototaxites is clearly not a plant, composed as it is of interwoven tubes just five to 50 microns across (50 microns is about half the width of a human hair). “With that anatomy, it suggests lichens, fungi or algae,” Boyce told LiveScience.

I like the idea that a lot of dead junk had built up for a fungus to eat. Certainly a lot of dead junk did build up, as evidenced by the huge coal deposits laid down during these eras. But why would a fungus need to be so freaking tall? Mysteries, mysteries. In any case: your fungal forest.

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Image: Prototaxite bland fungi this image is beautiful. Not exactly a forest, but prototaxites, eurypterids and an amazing vibe.

Answer 2

Trees are tall because they are competing for sunlight. A fungus that received all the nutrients it need at or below ground level would have very little reason to grow taller. But you want a forrest of fungi which requires tall branching structures. Fortunately there is a solution that fits your world and also solves the food source problem. Filter feeding. A tidally locked world is going to have massive continuous weather systems these storms would justifiably pick up vast quantities of organic matter, your fungi forrest could be situated at an eddy in this storm where the organic matter collects and settles back to the ground. There would be evolutionary pressure to catch this falling detritus first leading to tall branching canopies of fungi.

Answer 3

One thought that comes to mind is this: imagine that the planet isn't quite fully tidally locked but instead rotates very slowly.* Therefore on one side of the planet the Sun is always setting, but so slowly it hardly moves over a human lifetime, and on the other side it's rising. On the setting side there are (or once were) lush forests of normal Earth-like trees. Eventually the Sun goes down and those trees are cast into darkness, which kills them due to lack of photosynthesis --- but before they can fully decay they become encased in ice, where they remain for (let's say) hundreds of thousands of years as they pass around the dark side of the planet.

Your civilisation lives on the opposite side of the planet, where the Sun is rising. Those dead trees, encased in ice for thousands of years, are now nearing the sunlit side once again. It's still dark where they are, but warm air currents from the sunlit side have begun to melt the ice. Thus, the ground is covered in freshly uncovered and well-preserved dead plant matter, the perfect environment for fungi to grow. It's cold, so they grow slowly. (Otherwise they would just use it all up too quickly to reach any appreciable size.) Since there is always new dead forest emerging from the ice the ecosystem is stable and many species, including the giant mushrooms, have evolved to fit this unusual niche.

_{*Full disclosure: this might not matter if you're not worried about 100% plausibility, and I'm not 100% sure about the following anyway, but this situation might be quite difficult to achieve from an orbital mechanics point of view. When a planet becomes tidally locked it probably doesn't just rotate more and more slowly but instead starts rocking from side to side like a pendulum until it comes to a stop. However, it might be possible to achieve a very slowly rotating planet if it's influenced by the gravity of another body, such as a small or distant moon, or a second sun/brown dwarf/black hole etc.}

Answer 4

Think of lichens.

Lichens are a symbiotic form of life, fungi and algae. Trees grow high to reach the sunlight. Fungi don't need that. But algae does. Lichens today are rather small, growing on trees, great rocks or walls. But if there are no trees or walls, they have an evolutionary reason to grow up like plants or trees.

Algae don't grow large or form hard structures, but fungi can, if they need to. The lichen can grow high as a fungi to support its algae with sunlight. Lichens can form great and fantastic structures, quite well fitting in a fantasy world.

The fungi supports the algae with water from the deep, the algae support the fungi with sugar from photosynthesis.

You would not need dead waste as a food source, but you can do that additionally. Dead waste (from elsewhere or from dead or ill lichens, too) would rather be eaten by normal fungi instead of lichens. They would add another bizarre componente in this "wood".

(Picture taken from https://de.wikipedia.org/wiki/Flechte)

I am thinking about a plausible reason why there could be a region where normal trees and plants can hardly survive, but lichens and fungi can. Maybe some sort of disease affecting normal plants, but algae are protected by the fungi.

Maybe more plausible is an ozone hole depressing regular plants, but surviveable by lichens. That could add some story elements as the region would have dangerous UV light for people during the day.

At night, lichens and fungi could spend some surreal bioluminescent glowing light.

(Picture taken from https://en.wikipedia.org/wiki/List_of_bioluminescent_fungus_species)

Answer 5

Since fungi are not autotrophs, you need a food source. Maybe the forest is at a crucial pass and massive armies regularly battle over the spot. Thousands of casualties every month give food to the 'forest'. A passerby will see countless bodies with fungal tendrils growing into them. Old armor is half buried amidst the floor. Your fungi might even trap animals passing through the area to digest them as well, making the place hazardous to traverse alone.

Second possibility. You have a city whose waste is managed by a small fungal forest. The sewage flows out of the city to a nearby bog and piles up there. Fungi of increasing heights have begun to grow among this bog, decomposing the refuse.

Answer 6

Yes a "fungal forest" is very possible.

In fact, it is believed to have happen on Earth in the distant past. Before trees evolved there was grasses and among them large fungus. Some over 20ft high.

As to what they feed on, well, I think you are on the right path with fauna, mega or otherwise. There would also be spots with vegetation, bushes on higher ground. The leaves falling from them to the lower land can also provide a little "food". It is all very possible.

Answer 7

The reason fungi on our world use respiration to decompose detritus (and consume oxygen) is because of the endosymbiosis of the ancestor of mitochondria.

The reason for respiration among all eukarya, is down to the mitochondrion, which we all share. That ancestral bacterium dictated the use of oxygen. This made the algae and plants happy, because now their waste (oxygen) does not build up.

Your solution is simple. Create a different organelle, a different endosymbiotic event. You already have a different planet. If the event endosymbiosed a bacterium that uses nitrate instead of O2, or sulphate, etc. for its respiration, then the substrate can be different too.

In particular, if the original endosymbiotic event included a bacterium that uses fluorine for respiration instead of oxygen, (this has other problems but is an interesting exercise) then metabolism of additional carbon sources (including CO2) becomes possible.

Answer 8

Fungi need detritus to consume, hece you have them - on earth - as a part of forest ecosystems. Some fungi are specialised in organic matter that few other beings can decompose, like wood. Some even make peroxide, a powerful bleach!

So your question turns IMO into "How can I have a steady supply of organic material into an are where little other life survives. The answers of Vincent and Nathaniel go into that direction.

Here's my proposal: On a tidally locked planet, we'd expect a lot evaporation on the sunny side and lots of precipitation on the dark side. So most rivers will flow from dark to light. Now, if a river somehow accumulates lots of organic matter and is then - through a trick of geography - forced to meander into the twilight or dark zone, you could have your fungal biome. Plants won't thrive due to lack of light, but funghi could tap into the organic reach stream. If you want the fungi biome to look like a forest, have the stream underground, slowly seeping through a thick layerof gravel. The ground will be thick with mycelium, while the fungi push their fruiting bodies ever higher.

Now, we need a source of organic matter that's steady over a few millenia. I suggest that our river, before meandering back into the dark, flows through a sunny part of your world and gathers lots of plant matter. Maybe your fungi biome grows on the outflow of a large moor.

For this convenient flow pattern, we need a sicle shaped mountain range, paralell to the terminator (day-night line) with the belly pointing towards the sunny sides an the points to dark side. This will serve as a watershed our river has to flow around. Maybe there's the rim of a huge crater that was broken at a few convenient places? Or during an iceage, the glaciers on the dark side pushe a lot of ground towards the sunny side, creating a system of end moraines that now constricts flow.

Incidentally, the Münchner Schotterebene is a bed of gravel that was pushed off the alps over several glacials, in some parts the groundwater table is 40m below the surface. So there is a precedent for low groundwater table near heavily glaciated areas!
It gets better: the ground level falls to the north, away from the alps and the wholething finishes into a series of end morains, also there are a few moors in the north. The basic layout you need is not totally implausible!

Answer 9

You could have the a filter web made of, giant, Hyphae, basically a fungal root system covering the outlet of a stream or an ocean inlet, downstream from an elephant or whale graveyard. The hyphae feed on the effluvia flushed from the graveyard with every rain or tide and take up nutrients to feed the fruiting bodies that break above high-tie mark. The resemblance to a deep forest could be quite marked, with the hyphae forming trunk analogues festooned with seaweed and other detritus like the lichens seen in many forest and swamp biomes. As an inter-tidal environment the fungi could mesh relatively smoothly with land bound forest or mangrove swamp inviting the unwary to stumble into range of the incoming tide without ever realising their danger. From above you would see a canopy of mushroom/toadstool fruiting bodies extended up into the wind to spread spores to other feeding grounds wherever the wind blows.

Answer 10

When the dinosaurs died, many forests could have perished for 15 - 20 years in a row, so there would have been many tons of forests which had lots of mushrooms, millions of flies and beetles feeding of the giant dead animals for 10 years, lots of squirrels and other animals feeding from funghi and beetles.

If you had a forest that had a dark period every 2-3 years when one of the moons eclipses the sun or a super volcano erupted regularly, there could be forests that have major diebacks every few years and that become mushroom worlds for 1-2 years at a time, until the warmth and sun re-appears. any kind of cool cataclismic event that darkens the skies and provides lots of biomass would make mushroom forests.

any carbon rich source for example tar and oil volcanoes could cause giant mushrooms to have an advantage over trees. perhaps tsunamis wash away the forests every N years and make a mountain of wood someplace. mushrooms don't generate cellulose that's why they are not big.

Answer 11

How about if there were subterranean bodies of water supporting ecosystems of chemosynthetic life. The fungi could be growing down into these bodies of nutrient rich water or their outflows. Perhaps variations in the ecosystems would also cause variations in the fungi that grow or how they grow, thus giving regional variation to the "forest"?