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I have a desert world with high tectonic and volcanic activity. To the point where an ashfall is not an uncommon weather pattern. The ash itself would be very fine fertile ash. The ash also has a cooling effect on the planet so it is habitable despite being a desert planet. What I want to know is what effect would all this ash have on the evolution of the planets ecosystem? I'm already assuming all species would have an adaptation to prevent ash from messing up the lungs while breathing.

Note: This world will have humans(or something human like)

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    $\begingroup$ I tihnk you'll have to define 'desert planet' before a meaningful answer can be given, and perhaps indicate why you think its impact would differ notably from what is observed on Earth. $\endgroup$ – rek Feb 1 '18 at 23:24
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    $\begingroup$ By desert planet I mean much closer to the sun than earth is. With what would be uninhabitable temperatures except for the ash cooling it down to more manageable levels but still very hot. So the poles would have oceanic climates while the closer you get to the equator the less habitable it becomes, to the point where settlement is impossible at the equator. There is also less water than on earth. Lets go with perhaps 40% surface area is water compared to earth's 71%. $\endgroup$ – ArcWraith Feb 2 '18 at 0:13
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    $\begingroup$ Being closer to the sun isn't going to make your planet a desert. It's more likely to be hot & humid, rather like the Venus of early SF. What's going to make it a desert (assuming it started out more-or-less Earthlike) is having a low mass, so the water eventually escapes. Think something like a somewhat more massive Mars, so that the escape is slowed. (And FWIW, earthly deserts can be quite cold at night and during the winter.) $\endgroup$ – jamesqf Feb 2 '18 at 4:00
  • $\begingroup$ "What effect does this have on the ecosystem?" is way way way too broad. Entire libraries could be written on that subject. You need to narrow it down to something more manageable. $\endgroup$ – Green May 10 '18 at 13:57
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One way an ecosystem might evolve to deal with constant ashfall would be via fungi or bacteria. You would have to have something that consumed the ash, otherwise it would build up and quickly stifle anything and everything under its unrelenting, crushing weight. (Forests dump tons of leaves every year, but thanks to decomposition they don't build up. Ash doesn't decompose, as it's already partially decomposed via an oxidization process - that is, burning.) Finding a process for eliminating ash would be the most critically important part of the process.

You might also see plants change color (as they do in the fall) to deal with the predominant light wavelengths present in such a situation (they would trend more red instead of blue/green/yellow, if the sun were like ours).

I would also expect the plants to 'move' some in order to clear their leaves of the photosynthesis limiting ash.

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  • $\begingroup$ Can I get more detail on the plant colour change please, why would they change etc? I've tried to find things myself but haven't had a lot of success. Also in what ways could plants move to displace ash? Maybe just be easier to push around with wind? $\endgroup$ – ArcWraith Feb 7 '18 at 0:40
  • $\begingroup$ Plants currently move to track the sun link, or to consume animals link. Leaves change color in the fall to deal with less sunlight. link (You're welcome for the website link with Comic Sans font). As far as plants moving to displace ash, there could be any number of actions they could perform to make this happen, from leaves folding when they get too heavy to leaves retracting at night or to some other us. Flytraps use small hair like sensors. $\endgroup$ – hbomb Feb 8 '18 at 13:51
  • $\begingroup$ Would it also be possible that species that live in/on trees eventually start clearing ash away as some sort of symbiotic relationship? Or even just as they move among the branches to get at fruit? $\endgroup$ – Not the letter A May 9 '18 at 10:36
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Read Wikipedia

No offense, but Wikipedia has the whole thing laid out in greatest detail. No point in trying to research my own answer when there is so much there.

A few bullets:

  • Highly fertile: good for agriculture
  • Usually acidic, sometimes very acidic: bad for agriculture
  • It can weight alot: Roof collapse killed hundreds after Mount Pinatubo blew in the Phillipines.
  • Ash in water prevents underwater plants from getting light
  • Ash with high flourine content can kill grazing animals
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  • $\begingroup$ Yeah I understand that but I want to know how an ecosystem might evolve to deal with those problems $\endgroup$ – ArcWraith Feb 2 '18 at 2:24
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Not sure if this helps, but Brandon Sanderson's Mistborn Series takes place on a planet with heavy, nigh-perpetual ash-fall. The characters learned that they used to be on an Earth-like planet, but after a catastrophe:

  1. Plants all turned brownish colors and no longer flowered as long or as much (if at all).

  2. Species started having way more children, I think. Besides whatever the LR did to the Skaa, Tensoon mentions that the older generations of Kandra are fewer in number than the younger ones, despite Gen 1 and Gen 2 basically staying in the Homeland and never taking Contracts.

  3. I think there were less birds and fish?

    Vin grew up in Luthadel, but she and Reen traveled a bit as kids. I don't recall an instance where she mentioned or thought about how, when things were desperate, she'd catch pigeons/fish/stray animals/rats for food. I also cannot remember her ever mentioning seeing birds or fish, and birds are pretty common in urban areas. I also cannot recall her mentioning eating poultry or seafood at any of the balls, though that may just be my memory failing me.

    Beyond that, birds would either need to preen way more often to get ash out of their feathers or they'd become unable to fly due to issues with balance and weight if the ash got stuck. (There's some cool and kinda sad stuff about how important it is for birds to keep clean, if you want to look it up.) And fish could quite possibly get ash stuck in their gills and suffocate- it happens with sediment from river bottoms sometimes.

    It's also entirely possible that, as crops failed and food became an issue around when the LR took over, people hunted a lot of animals into extinction.

  4. In book three, the characters were looking for food sources and someone mentioned growing fungi to combat the food problem. This is an idea that I think would make sense as fungi can be grown indoors/away from the ash.

Of course the story is fantasy, so I'm not sure how accurate this is.

Your planet has to deal with lots of tectonic activity too, so there'd be issues with anything underground. Food caches, power lines, sewers? Animal burrows, water, food caches? Nope, that earthquake just sealed off the area/released toxic gasses/crushed everything so no one could recognize the area. (And, assuming you mean hot/sandy desert, filled the place with sand, too.) Ooh, and sinkholes are a thing. Yeah...

Speaking of the Mistborn, the high volcanic activity would probably block out sunlight for most of the day/week/month with ash- if it ever clears up. This could, eventually, lead to your planet becoming a snowball.

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  • $\begingroup$ I have read the series. The brownish plants were there. The Skaa did have more children but that didn't have anything to do with the ash. Nothing was mentioned about fish, birds or fungi and there are microbes who break down ash. And of course we get to see what happens when the ash starts piling up faster than it can break down $\endgroup$ – ArcWraith May 9 '18 at 2:58
  • $\begingroup$ @ArcWraith. I elaborated with the birds/fish thing. You're right about the Skaa, but it happened to the Kandra too, I think (and possibly the koloss?) - and generally, having more children does make it more likely for some to reach adulthood. $\endgroup$ – Not the letter A May 9 '18 at 11:39
  • $\begingroup$ Neither Kandra nor Koloss breed naturally. Although Koloss are altered to do so by harmony but then the ash is gone $\endgroup$ – ArcWraith May 9 '18 at 23:27
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An ecological enhancement for many of the other answers: trees that grow in a parabolic shape which sheds ash in a circle around them, much like some Earth trees shed rain in a circle above their most active roots. (The "drip line".)

Animals are attracted to the ash-free bases of the trees, and provide fertilizer. Make the trees big enough and you've got the start of a decent ecosystem.

With constant ashfall burrowing animals will have an advantage, look at the burrowing ancestors of turtles for weird but plausible examples.

The locations of the volcanoes and the standard effects on prevailing winds (mountains, bodies of water, ice caps) lead to variegated ash fall patterns across the planet, leading to all kinds of conflicts over resources and land that can drive plot.

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How thick is the ash fall?

If it is a light dusting then plants will likely evolve slicker leaves so teh ash doesn't stick and their leaves will likely hang down so the ash doesn't have a horizontal surface to rest upon.

If the ash is up to an inch thick then you will see a combination of perennial plants and trees. Low plants and grasses will likely evolve to either go to seed in response to the ash fall or to use a growth burst to break through. Saplings that last through one of two ash falls will be tall enough that as long as the leaves are designed to not hold the ash, they will survive without too much problem.

Animals will have a rougher time of it.

The ash will get into their breathing passages and likely cause medical problems. Also, unless they feed off of trees, they will evolve to deal with food that regularly gets buried and dies. So, animals will likely dig though the ash to find edibles and will time the birth of their offspring to when new growth pops up through the ash.

The thicker the ash, the longer the recovery period gets and the harder it will be for the natives to adapt to it. Also, the ash stresses the ecosystem enough that if other stresses come into play, the ecosystem may collapse.

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