This question is inspired by a comment by PcMan

Imagine you have an Earth-like planet, except it is just a little farther away and has longer days. Instead of having a tropical equator, the planet now has a temperate equator with extremely cold latitudes. The planet has a day 16 times longer than our Earth's, so there are periods of day and night that last over two weeks. At night time, the temperature would be below freezing, far too cold for detritivorous insects.

Therefore, the insects would only thrive/breed during the long daytime, and die off during the night. The decomposing bodies would be plenty of food for night-time fungi.

In theory, fungal forests would be a plausible alternative to the insects at night, where they would wax in population at night and wane in the day. I define a fungal forest as a dense collection of fungi organisms. This would be in the form of decomposing animals and plants, such as bodies or rotting tree trunks.

Are seasonal fungal forests like this possible?


What Do The Mushrooms Eat?

It's important to remember that fungi are heterotrophes. Like animals, they must get their energy by consuming other organisms. Forests are typically made up of trees, which are autotrophes: they can make their own food from the sun.

Most fungi eat decomposing plant matter. Most of the mushrooms you might be familiar with at the grocery store begin life as a spore that has landed on some dead plant stuff, either a log, a pile of leaves or straw, or else commercial grow media. The spore grows into a network of myclium that consumes the plant matter, and when the fungus has had its fill, it fruits mushrooms which spread more spores and then often dies of starvation, having completely exhausted its food supply. A log that has been eaten by fungus cannot even be used as fuel, it is so thoroughly consumed.

For your mushroom forest, you will need to explain where all of these massive mushrooms are getting their food from. This could be an opportunity to add some additional ecosystem elements to your world! Perhaps some vast horde of migrating animals seasonally comes to this forest to procreate and die, leaving their corpses to be consumed by the mushroom trees. Or maybe they just come here to poop - before carrier pigeons went extinct, they used to blanket [tree-filled] forests with so much shit that you can tell what years they migrated over a particular area just by looking at the growth spurt in tree rings.

Prototaxities: Real World Fungus Forests (maybe)

400 million years ago, there were likely no plants taller than 1 meter. Plants had not yet evolve the ability to make lignin, so they were structurally limited. And yet the fossil record shows evidence of large, trunk-like organisms that grew upwards of 8 meters! These are the prototaxities, and they are thought to have been fungus. It seems they did indeed grow as a sort of forest (sometimes) (maybe). What did they eat? That seems to be a heavily disputed issue. One prominent theory suggests they had a symbiotic relationship with algae, which might have provided photosynthetic energy. However, symbiotic relationships between algae and fungi are usually called "lichen", not "mushroom".

A Final Suggestion

Speaking of millions of years ago, when plants eventually did evolve the ability to make lignin, it sparked a global extinction event. At first, few if any organisms on earth were capable of breaking lignin apart, so as plants died there was no one around to decompose them. These dead plants piled up everywhere, refusing to yield their carbon back to the atmosphere and sparking a horrific climate catastrophe. I imagine that whichever organisms first evolved the ability to break lignin apart must have really gorged themselves though! Maybe this could be the case for your mushroom forest: a mega-huge mushroom species discovered an ancient, buried forest and now feeds on millions of years worth of preserved wood. Just a thought!

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    $\begingroup$ To add to this, mushrooms are fruiting bodies, so the size of a mushroom may not reflect the availability of available organic matter. A comparable example in plants might be how the tiny agave produce colossal fruiting bodies when they breed. Granted they save up for a hundred years and die after this. $\endgroup$ – user2352714 Dec 28 '20 at 3:00
  • $\begingroup$ @user2352714 Excellent point! The energy for making enormous fruiting bodies must come from somewhere, so I assumed the supply of energy must be large. I had not considered the alternative you propose, that the period of feeding between fruiting could be long. $\endgroup$ – Pink Sweetener Dec 29 '20 at 1:52

Fungi don't like the cold either.

On your world it is below freezing at night and too cold for bugs. That is cold for all water based life. Fungi too will power down when it is below freezing. I am reminded of the stories of Shackleton's hut in the antarctic, preserved in the cold for decades until recently.


For 90 years the dog's carcass remained where it fell, a collar and chain still around its neck. For most of that time much of the flesh and fur remained intact, preserved by Antarctica's extreme cold. And though gale-force winds have beaten ice, snow and sea salt into the sides of the hut, the foodstuffs inside remained intact.

Now it appears a changing climate is threatening the history housed in these huts at the far end of the world, simple structures that many place among the greatest monuments to courage and the human longing for discovery.

With the weather warming on Ross Island, mold and fungi are blooming in all three of the explorers' huts -- some so mysterious scientists don't know what they are. They are rotting the timber of the huts and thousands of artifacts inside them. The dog is now reduced mostly to a skeleton.

A fungus forest is a fine idea but I don't think it will like it below freezing any more than the bugs.


Yes, they'd be possible. Mushrooms grow their fruiting bodies remarkably quickly and could definitely do so in the 8 day-long period of sunlight/moonlight. Of note, you wouldn't have massive mushrooms, though. They wouldn't replace trees; there would just be more of them! Also of note, the majority of a mushroom is the mycelium which is hidden below ground, so that may be much more prominent in your world. I would also add that insects are a major contributor to biomass and are a prime thing that mushrooms (and other decomposers) decompose as well as a major source of food for secondary consumers. There would have to be something to replace them or else the ecosystem just wouldn't work.


like the ones in mincraft, well, the answer is yes, they could start growing in spring, and die away from cold in winter, but they need enrgy, this energy is transported by mycelium networks, but where does it come from? well, other forests, maybe animals, etc, this problem i have not been able to solve, maybe they evolved some kind of chlorophyl? or eat the poop of insects and other animals?, another thing would be the growthrate, which is very plausible, as seen in other mushroom, the stability can change depending on what the networks feed the mushroom, also, it would more likely be a hivemind of mushrooms

or not so big a mushroom, yes to, but these would need other compounds an example could be in https://criticalconcrete.com/building-with-mushrooms/ , here it gives an example of heat insulator, so the mushroom can trap the heat inside itself and survive


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