You're not wrong about the diminished abilities of a desert to hold water. More people drown in deserts every year than die of thirst. When it does rain it pools up and can easily create flash floods. The major problem is if you do try to start building any topsoil, these types of floods can wash away your years of work. It's a hard problem because you're both in desperate need of precipitation and desperate fear of it
Techniques that could be used to combat this are things like the waffle gardens[0] that Zuni people have used for a long time, olla pot irrigation that have been in use in China and Northern Africa for over 4,000 years, and complex swale systems, or terracing systems like the Incans used to basically turn deserts into fertile ground[2] and might be the reason we today have potatoes, tomatoes, corn, beans, peanuts, sweet potatoes and a large number of other crops domesticated in the Andes
I really think the biggest challenge is just shade though. The worst thing you could possibly do for soil is expose it to direct sunlight. One "geoengineer-y" idea I toy with that keeps coming up for me is what if we just built a bunch of large boxes made of wood or bamboo some other biodegradable material and just left them in the desert. All that you really need is something like the structures that shade covered parking lots. If you just make some large, flat, cheap structures like these you'd be able to provide what's possibly one of the most valuable resources in the desert: shade. Ultimately if you manage to start a soil ecology up, the whole issue solves itself. Soils inoculated with mycorrhizal fungi hold 50x as much water as those that don't; the soil activity of bacteria, fungi, protozoa, nematodes, etc also turn the large grained sandy soils into more loam-y soils that can support many more life forms and plants; the fine roots of plants that tend to grow in soils like these hold together soil better so less topsoil gets lost; plants that grow with mycorrhizal fungi are less susceptible to drought (as well as frost and basically every other stressors you can think of) and have much more access to nutrients.
Basically all our problems go away if we can just get soil going. And plenty of desert plants already know this. Creosote bushes, nara melons, and the nitre bush are 3 examples that immediately come to mind. All of these slow growing plants have the strategy of simply providing shade and holding as much soil together as they can. And over time an incredible diversity of soil microbiomes form around the roots of these plants. The nitre bush also forms nabkhas[3] that capture other debris flying around and over time lessons the harshness of the desert winds, thereby lessening the rate of topsoil loss.
Nature already has solutions. If we could just kickstart the process by providing the right microclimates we might be able to help these organisms stand a chance against the forces of desertification
[0] https://www.notechmagazine.com/2021/11/waffle-gardens.html
[1] https://www.nativeseeds.org/blogs/blog-news/how-to-use-olla-...
There are ways to do this without creating bogs, and work off of the monsoon rains that come through these regions.
If wasteland can accumulate organic material, and start rebuilding the soil, it starts retaining more water, which brings in more vegetation. This reverses desertification. There are some good examples of this in India. There are parts of the Arizona central canal which accidentally created bearms that also started this effect.
My favorite way of developing fungal-dominated soil is starting with a basin (for retaining water; I'm in AZ), and filling it with wood chips from chipdrop. The trees I do this with all love it.
I know someone who started sourcing the waste product of mushroom cultivation. These are wood chips that have been "spent", (harvested the fruiting body) but would still have the mycelium to jumpstart this process.
For growing annuals though, I think biochar is still a great option. Another possibility is, rather than looking at temperature, look at rainfall. Tropical forests gets a huge amount of rain, washing away nutrients. Biochar helps retain that. It might be that temperate rainforests would benefit more from biochar than building up fungal soil.
This seems like an impossible claim to back up but I would absolutely love to read if you have anything that would
It's well-known that in general in the ecological succession of the soil food web, soils "start" out more bacteria dominated (corresponding with nitrogen generally being available more as nitrates and nitrites) and slowly turn to being more fungal dominated (corresponding with nitrogen being generally available more as ammonium or other harder to access forms that generally come along as the food web gets increasingly complex and trophic layers build up)
By "start" up above I of course mean after a disturbance like a fire since we're talking about secondary succession (if we were talking about primary succession we'd be talking volcanoes and lichen turning rocks to soil). Therefore, I would expect the pattern to have a lot more to do with the amount of disturbance different areas are exposed to. Perhaps a lot of tropical areas can have intense monsoon seasons, but there are just as many examples I can think of of temperate areas with regular disturbances.
In addition, I tend to think of the incredible diversity of orchid species in the tropics and many of these species often rely on a specific fungal species to even germinate. So I would also expect to see more diversity both in fungi and bacteria in the tropics
Is any of my line of thinking on this misled? Would love to have it pointed out!
Tropical forests are bacterial, temperate fungal. I don’t think it’s an accident that terra preta (a biochar + ? complex of soil) is found in Brazil.
It’s also a reason we have to be careful about global warming. Temperate forests make great carbon sinks, tropical do not. If we tip more land into tropical we lose a powerful method of remediation.