As above, so below. Picture in your mind, the tree of life - with a canopy stretching as wide as its intertwined roots. This image is, in fact, quite literal & representative. The breadth and width of the canopy of a tree is equal to the breadth and width of its roots system below the soil. Next time we sit in the shade of a great big tree, we can imagine the massive root network below our feet! How beautiful is that??
With that visual in our minds, we can understand this amazing phenomenon. When the limb of a tree is severed - by humans, wind, storms, or another falling object - the tree experiences a paralleled amount of root die-off below the soil. When roots die in the jungle or forest, there is certainly no one coming through to pull those roots up, like a home gardener may do. The 'waste' from roots are a direct food source for the soil microorganism & fungal network, who take up the roots decomposing sugars as a buffet of energy & nutrients.
With this basic understanding, we can see how the soils of undisturbed forests and jungles get stronger and stronger with time, and how a storm that knocks down tree limbs is part of nature's cycle of providing rich nutrition to other plants.
Let's move into how we can apply this concept into our home gardens, community lands & farms.
If chopping tree limbs causes a parallel root die off, then can we 'stack the functions' of pruning specific trees?
Yes, certainly. Let's look at nitrogen-fixers. Nitrogen-fixing trees are a go-to solution for healthy soils in regenerative agriculture and permaculture. Why? Because their roots host a bacteria with small nodules that are able to capture atmospheric nitrogen from the air and convert it into fixed nitrogen, aka basic plant nutrition.
We also know that nitrogen-fixing plants store that nitrogen in their bodies themselves, not so much the soil around them. Nitrogen is stored in their leaves, their limbs and their roots.
We can plant nitrogen-fixing trees and intentionally prune them to gain the many benefits of nitrogen rich leaves to use as mulch, sticks to use as firewood for a rocket oven, AND roots to die off and feed the soil food web with rich nitrogen for the accessible uptake of other plants.
This, in permaculture, is a method known as CHOP & DROP. Chop the limbs off of various nitrogen-fixing perennials and trees & drop the biomass on site, to release its nitrogen to the soil. Simultaneously, we benefit from the root die-off that feeds the soil microbiology. Chop & drop is an effective way to build soil before the rainy season sets in, as all that nutrient rich biomass will breakdown into humus with the rain. It is also an effective source of mulch, any time of the year. On very barren or degraded landscapes, chop & drop is a strategy for accelerating the natural succession of that land. Let's take the examples of thistles in my home climate - the temperate Pacific Northwest. Thistles are a pioneer species that arrive after a natural distaster like a fire, floor or landslide. Over many many years of thistles growing & dying, growing & dying, enough nutrient would build up in the soil to host more complex plant life. We can use chop & drop to accelerate that by chopping the weed just before it grows its seed head. When we stunt the weed that way, it will be forced to put more energy down into its roots to be able to set seed again. Again we cut it the plant before the formation of the seed head. This cycle will repeat several times until the weed gives up and dies back, thus providing the soil nutrition from root die-off and deep & large air pockets from where the roots have decomposed.
While one can use just about ANY perennial plant in a Chop & Drop process, the best selections are plants that are either nitrogen-fixers or dynamic accumulators (plants which have a characteristic of mining trace minerals from the soils).
Chop & drop is an especially revolutionary approach when it comes to dealing with invasive weeds on barren soils. Too often do weeds get cut down and swept away, off site. Thus disabling the cycling of nutrients back to the soil that needs it. Instead, chop weeds before the seed head forms and let that nutrition add to the overall slow build of soil health.
Great CHOP N DROP plants in the tropics:
-Perennial pigeon pea
-lemongrass & vetiver grass
Time to buy that machete, eh?