Fire as tool for growing food plants

This might be interesting for al you forest dwellers.

https://phys.org/news/2017-11-archaeologist-idea-prehistoric-people-southwest.html?utm_source=nwletter&utm_medium=email&utm_campaign=weekly-nwletter

most prehistoric groups in N. America that we know anything about seem to have employed controlled burns over large areas as a way to drive game, manage land and harvest mast. In the Appalachians where chestnuts dominated the canopy fire was a crucial method of mass harvesting the nuts. One theory is that they set fire to the woods and hunted the fleeing game (both on foot and from boats and rafts) while non hunters followed behind to gather all of the charred nuts.

I love growing on the ground where I have burned the branches pruned from the fruit trees. It's highly fertile, and generally free of weeds.

article  and some comments also found here:

https://permies.com/t/73037/Fire-corn-key-prehistoric-survival

Very interesting article. It is easy to believe that scholars have been too willing to assume indigenous peoples readily adopted techniques that can be seen as analogous to modern agriculture. People in the SW would have had ready access to a source of calories and protein--pinyon/pine nuts--very comparable to corn, but not so with dark green leafy vegetables other than amaranth and lamb's quarter. And fire as a tool was much more attractive before the availability of iron and steel. Most elderly Dine (Navajo) growers I've met are much more comfortable with burning crop residue and weeds than using them as mulch or to build compost piles. On the other hand rapid oxidation of organic material that could be composted or used as mulch has always seemed a waste to me. And my experience in the high desert of New Mexico has been that disturbing garden soil just enough to remove grasses that can outcompete wild greens and applying moisture and mulch results in a proliferation of amaranth, lamb's quarter and to a lesser extent purslane. So I'm left with the question of whether, given the tools now available, it is wise to use fire in this way.

This article from Northern Arizona University indicates a cost/benefit analysis of fire as a tool is complicated. It's not clearly stated how all the factors listed play out over time, but this seems most cogent to me: "Forest fires usually decrease the total nutrient pool on a site (the total amount of nutrients present) through some combination of oxidation, volatilization, ash transport, leaching, and erosion...Though fire can diminish nutrient pool sizes, nutrient availability often increases. Soil fertility can increase after low intensity fires since fire chemically converts nutrients bound in dead plant tissues and the soil surface to more available forms or the fire indirectly increases mineralization rates through its impacts on soil microorganisms." In other words there are short term benefits (nutrient availability) at the cost of long term deficits (lower total nutrients). With our access to steel hoes, wood chippers, compost tea, and other modern tools, I can't justify using fire now, no matter how useful it was in the past.

I've got a book written by a scientist from Utah named John A. Widtsoe around the turn of the century called "Dry-Farming : a System of Agriculture for Countries under a Low Rainfall".  (He was also a high ranking official in the LDS church, so if you look up his writings you will see both scientific and religious writings.  It isn't a mistake, you have the right guy).  He did a lot of research on desert soils and came to the conclusion that the common model of three layers of soil (topsoil, subsoil and bedrock) was not appropriate for desert soils.  He decided that the model was developed in well watered areas like Germany or the eastern half of the US.  He didn't observe the differentiation in desert soils described in the classic model, but found that their fertility extended quite deep.  My thumbnail summary of his book is that the humus in the topsoil is necessary to hold the nutrients in areas of abundant rainfall, but that lack of humus in the desert is less of a problem because it isn't subject to anywhere near the same amount of water dissolving and removing nutrients.  Of course, there is a lot more than that in the book, but I read the book quite a while ago and that was my take away.

If this is true, it doesn't mean adding humus to desert soil is a bad thing (if nothing else, humus on top of the soil will prevent drying out, but it does provide a possible reason why desert soils, which are often very low in humus are still very fertile.  Also, humus still is a great help in holding water in the soil.  

Before we throw out the baby with the bathwater, maybe we need to reexamine the use of fire.  It was the most used method of ecosystem adjustment in the new world, and while they were a stone age society, they were a pretty savvy stone aged society and developed some pretty cool systems and crops.  Small, low intensity fires are less likely to burn to ash, leaving a lot more plant detritus and such fires are less likely to open an area up to much erosion, especially if the fires are timed so that there is enough moisture to sustain an immediate weed bloom of edible weeds.  

My wife's uncle grew up around Yosemite National Park back in the 30s and 40s.  At that time he said he watched the local indians burning off fields for their oak trees.  He said they would pick a cool, dampish foggy kind of morning in the spring and move with the fire, protecting the plants they wanted to not disturb and pulling up or otherwise destroying the ones they didn't want.  In such a case, you will loose some carbon, but there won't be much erosion and if it results in a big weed growth (from weed seeds in the soil seed bank waiting for a fire to sprout) the resulting weed growth may deposit a lot more plant material than was burned.  

(I'm just suggesting this as a possible scenario, I not emotionally invested, so if you see a flaw in my proposition, you may proceed to mercilessly rip it apart with the knowledge that it won't bother me, much.)

Walter McQuie

You make a good point - It's indeed possible that with modern tools and wel planned activity you may duplicate the results you have with the use of fire.

Still - that idea is probably difficult to verify/falsify if for no other reason that many ecosystems are adapted to regular fires - some seeds actually need fire to sprout. If you happen to harvest something usefull from such a type of plant, fire becomes a necessity.

For climate reasons we should use fire as little as necessary. Keep in mind that 'modern tools' often include combustion engines - so using modern tools to circumvent the necessity of fire in an ecosystem may be costly in fuel and perhaps in CO/CO2 as well


Mick Fisch

I have zero experience with desert soils. Desert soils are probably not always fertile but let's assume for this discusion that they are. I would offer a different mechanism for the abundant availability of nutrients. Even in the hottest and driest deserts there is still some water. Capillary water and heat are sufficient to speed up weathering of mineral grains but capillary water does not flow much trough the soil. So the nutrients from the broken down minerals are available for plants but the do not wash out fast. Also the nutrients may be weakly bound to surface films on f.e. sand - think desert patina.

A classic example is Egyptian carved stone/buildings and such. When these ar found on the surface, never been buried for long in the shifting desert sand these are often in great shape even after 2 or 3000  years. However if buried for a long time in sand the carved stone is rounded. This observation is generally attributed to groundwater accelerating weathering trough salt deposition.

In Belgium we have some areas with old copper telephone wires in the ground. These cables are being fased out nowadays. The insulation of the copper cables has degraded. In summertime we have the occasional drie spell here. When such a dry period ends there are generally more problems with the phone connections. This is often attributed to chemical weathering

Excellent points Erwin! Thanks.

My interest and recent experience is in local market scale food gardening. Using a two wheel tractor to incorporate lots of organic matter into high desert soils and build raised beds then growing no-till using only muscle power. Kind of like temporary use of a track-hoe or such to lay out a food forest. We grow then chop and drop cover crops, harvest grass broadleaf and legume volunteers from around the property for mulch and compost, import some hay and manure, coppice and chip some of our fast growing riparian trees for mulch, feed lots of greens to worms and chickens, brew up teas, etc. all to feed the soil food web and harvest a surplus for a larger community. Don't see fire fitting in. Except in the kitchen.

(At least)The high desert soils along this part of the southern edge of the Colorado Plateau are very fertile in the sense that they are young geologically speaking, and therefore contain many of the mineral sources of plant nutrients. Some are indistinguishable from the rock dust added to played out soils found in humid temperate areas. Some are sandy clay loams that have decent capacity to hold on to plant nutrients, if they are present. But water is scarce here and has been for long enough that organic matter content is typically very low. As a consequence these soils are not a very hospitable locale for soil food webs. So there typically is not much of the biological activity that is needed to naturally transform the elemental constituents of minerals into forms available for plant roots. More organic material makes a better physical home for the soil food web, holds on to water that must be present for biological activity to thrive and then holds on to the plant nutrients that result from it.

Here's a permies post to explore for an explanation of my focus on the biological process in the soil over the physical mechanisms breaking minerals into smaller particles: Teaming With Microbes by Jeff Lowenfels and Wayne Lewis, especially the second video--Ingham Common Ground 2012. Bryant Redhawk covered this territory better than I could recently on permies so I'll just leave it at that.

Yes agree! but you would probably know that fire will sometimes be an enemy, at times a friend, and frequently its effects will be mixed between the two extremes. One great truth of this environmental age is that it is far better to complement natural systems than to manipulate them for single-purpose gain.