Woah man, that's a trip! Cool story for sure. Interesting thing about "folklore" from civilizations as old as Mexico; there is typically much truth in them. The "guardian tree" definitely makes a lot of sense. It is something I have personally witnessed in not just my yard, but the desert straight across from me. Living out in the desert, there is a lot I've observed.
Don't feel the need to read the following, but these are things I've learned observing the way things work natively in the desert. I do my best not to be so long winded, but you never know what information will help someone.
Just consider the roots of the "guardian tree", and more importantly, how far they not only reach out, but also how deep they grow. If you'll allow me to, I'll get into that concept below when talking about observations I've made about living in the desert and observing the root masses of things that grow out here.
The absolute most important thing about trees that large is their root mass, like you said. But not just transferring the water,
but imagine the soil web living around those huge roots! The soil web is likely hundreds, possibly even thousands of years old, just as the roots are.
How we do living soil when we start off, we're attempting to "cultivate" microbiology within our soil. Literally giving the soil life. It is something that we need to create and facilitate when there is no life in the bales of Peat Moss/coco, or the various amendments available..
But with such large trees (and root masses by proxy),
you can effectively "tap in" to a soil web that already exists, and has likely existed since before many of us were even born. Dig up the top soil around any large tree and you'll see what I mean; has that lovely compost smell that is associated with a living soil. The biggest lesson I've learned since using living soil would be this;
it is much easier to tap into something that is already there, as opposed to attempting to create it by yourself.
It is also about what you
don't see, as opposed to what you do see. In this instance, the roots of the "guardian tree"
. Imagine a humongous soil web living underground; a massive civilization that we cannot even see, let alone fathom, that spans dozens (sometimes more) feet in diameter! As a result of this, one could literally do nothing but dig a hole and throw a seed/plant in it. Eventually, the roots of the new plant/seedling will meet up with the 10-100ft diameter soil web established underground centuries ago. At that point, success is guaranteed.
Take these photos of my backyard, and the desert behind me, for reference.
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Two very interesting things I'd like to point out about the photos above.
1) The trees in my yard are the same Palo Verde and Mesquite trees that are way out in that desert field in the back. Yet notice how much more vibrant and healthy the ones in my yard look.
2) Look at the ridiculous amount of trees out there in the desert; growing with nothing more than water from monsoon season. Sometimes going many months without water, yet they still survive.
Whether it is my backyard, or the desert behind my yard, you can see the concept of the "guardian tree" working. However, what is really going on is that all of the tree's roots and, more importantly, the microbiology attached to them, are all working in tandem with one another.
The trees in my yard look better because I've spent the last year not only growing plants in my yard, but watering constantly and consistently.
Interesting thing about the desert; the desert is actually the perfect place to grow plants. The only thing that native desert is missing is organic matter, and water. Many attempts at growing here will be met with plant death. However, those plants deaths are not in vain, as they will eventually decompose into organic matter that will sustain life in the future. Then once a consistent water supply is added, you get amazing growth.
Same principle with the roots vastly spreading out underground. The roots from my trees are likely underground everywhere, covering every sqft of my yard with roots completely out of sight. I can dig a hole, sift the native dirt of large rocks, mix the sifted dirt with soil from my pile, refill the hole, and get near instant and guaranteed success. Why? The roots, and the enormous civilization of microbes living underground that my new plants "tap in" to.
What's more, consider the drainage of desert dirt and sand. Not sure if you've ever witnessed intense monsoon rainfall, but it is very humbling. See that street there in the photos above? It turns into a literal river, and I'm not even exaggerating. It becomes a literal river; 1-2 ft tall river completely covering the street to the point where you can't see it, and that flows so quickly that it can carry a car off with ease.
But more astonishing than the rivers from the rainfall? How quickly all that water drains. Within 6-12 hours of the monsoon storm, the water is completely drained and underground.
Water always follows the path of least resistance, right? That means that underground in the desert sand/dirt, there is a literal path of "least resistance" that the water will always take. This results in all of that water pooling underground, resulting in an underground reservoir of water.
This is how the desert plants survive, the underground reservoir of water!
The only plants that survive out in the desert are cacti, and the Palo Verde and Mesquite trees. Why? Their enormous root masses! Not only do all of these huge root masses intersect and interact with one another, helping each other out,
but their huge roots are also large enough to dig into the ground deep enough to find those underground reservoirs of water!
And by large roots, I mean it.
Mesquite taproots can be up to 150-175 feet long, and their roots can spread to nearly 50ft in diameter! Even more interesting? Mesquite and Palo Verde aren't technically "trees", but rather enormous legume plants.
So, 150ft deep with 50ft radius, one mesquite tree can potentially have up to 27500 feet in root mass, and by proxy a 27,500 foot soil web to "tap in" to!
And remember how I mentioned they're legumes? They do in fact fixate Nitrogen into the soil! Just consider how much Nitrogen is coming from a root mass that can potentially be that large? Not as great as it sounds, unfortunately. I planted 3 raised beds near a Mesquite tree, expecting benefits of shading, but not knowing they were actually legumes and not "trees". They all had excess Nitrogen levels, no matter what. If anything grew in those beds, they'd never bloom due to the high N levels. And that's if they even grew. Mesquites can drink up to 20 gallons of water
per day, so they'll take loads of water from any plants nearby.
Consider that I live in the low desert in Southern Arizona, so one's mileage may vary depending on their own environment and/or circumstances. That said, I recommend everyone study their native plant life; learn what it does, how it works, and how it will interact with your garden.
Truly sorry if this wall of text was more than asked for, but one can never know what information will be useful.
All the best, and as always, happy growing to anyone reading!