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Fruit Tree Polycultures - Fungal or Bacteria dominant soil?

 
Ben Bishop
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I was listening to Sustainable World podcast today (great permaculture interviews!) and Doug Weatherbee was on talking about soil health. A question popped into my head that I was hoping someone out there could answer. Since soils either tend towards bacteria dominant, fungal dominant, or a blend of the two, does it make sense to try to make guild polycultures of plants that require different types of soils? In other words, would your fruit tree and your woody shrubs prefer fungal soil but your ground covers and herbaceous layer prefer bacterial? Are you compromising the health of some of your plants if you settle for a blend?
 
Zach Muller
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Ben Bishop wrote:I was listening to Sustainable World podcast today (great permaculture interviews!) and Doug Weatherbee was on talking about soil health. A question popped into my head that I was hoping someone out there could answer. Since soils either tend towards bacteria dominant, fungal dominant, or a blend of the two, does it make sense to try to make guild polycultures of plants that require different types of soils?


Maybe, in open areas you maybe have a pasture with grasses, legumes, annuals, wild flowers and other stuff that works together, and in an area with more trees you would have all your different layers that could be filled with various different plants.


Ben Bishop wrote:
In other words, would your fruit tree and your woody shrubs prefer fungal soil but your ground covers and herbaceous layer prefer bacterial? Are you compromising the health of some of your plants if you settle for a blend?


I am not sure if those plants 'prefer' one or the other, they are each related to the soil conditions of their natural habitat. My understanding is that you will not be compromising any plant health as long as you have a living cycle of microbes. If there is an imbalance between bacterial and fungal then they will naturally balance out.
 
Ben Bishop
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Zach Muller wrote:
I am not sure if those plants 'prefer' one or the other, they are each related to the soil conditions of their natural habitat. My understanding is that you will not be compromising any plant health as long as you have a living cycle of microbes. If there is an imbalance between bacterial and fungal then they will naturally balance out.


Most of the soil people I've talked to say that trees and woody shrubs grow better in fungal dominated soils due to the higher levels of available carbon amongst other reasons I'm sure.

I bet you're right in that a balance will be struck naturally. But it would stand to reason that if a tree would grow best in a fungal soil and you have it surrounded by all sorts of plants that grow best in, and create the conditions for, a bacterial soil, there would have to be some kind of sacrifice one way or the other.
 
John Polk
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I have pondered the same question myself, and sadly, I do not have an answer.

Perhaps this is one of the reasons that edge is often where the largest number of species usually occur naturally.
There is enough of each fungi and bacteria to satisfy both, but not enough for one to dominate.
Just as a savannah can be such a productive area. A blending of grasses and trees.

It is very common practice to recommend putting a shovel full of forest soil around newly planted trees.
This inoculates the soil with the fungal species that promote best growth for trees.
Likewise, a shovel full of compost for your other plantings.

Certainly, some plants will not perform at their best in the 'wrong' environment.
I would imagine that most shade tolerant plants are well adapted to a fungal environment by default, but not the sun lovers.

For a mixed planting under fruit and nut trees, I would tend to err in favor of the trees - that will be the bulk of food in that system.
A lone tree amidst sun lovers, I would favor the sun lovers.
As everything in life, there is always a compromise.
 
Michael Cox
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I can't recall where I read it but:-

Grass is a vigorous competitor for fruit trees
Grass does not like fungal soils (eg deep wood chip mulches)
Wood chip mulching our orchard trees has helped:

  • supressed the grass in the root zones
  • added fertility and moisture retention
  • allowed us to establish guilds by planting into the mulch
  • converted the soil to fungal dominance


  • Can I pin the improvements we have witnessed on fungal dominance? Not exclusively, but the overall effect has been excellent. I'm looking forward this year to globe artichokes, strawberries, comfrey and walking onoins from beneath trees I used to mow around.
     
    Johnny Niamert
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    According to the book Teaming With Microbes, most perennial plants prefer fungal dominated soils, whereas most annuals and grasses prefer bacterial.

    I can say without doubt that comfrey, for instance, loves heavy wood chip mulches.

    I always try for a balanced soil, compost, tea, etc, though. I prefer to let the plant and the microbes figure it out.
     
    James Colbert
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    I have noticed that most things grow very well in fungal dominated soils. I have used quite a bit of wodchips in the past on my garden beds and the plants love it. My thinking is that shorter lived species of plant do not have as much time to form beneficial relationships with mycellium and thus do not benefit to the same extent as perrenial plants. On the other hand all of that mycellium moves around a lot of water and nutrients making it possible to grow polycultures which work together in concenrt thanks to the middle man of mycellium. If I had to choose one I would probably go with a fungal dominated soil.
     
    Mike Hoag
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    In addition to Teaming with Microbes, there is some discussion of this in Edible Forest Gardens and in the Holistic Orchard. We designed with this in mind. We have a fugal-dominated food forest, under "fungal duff" management, for woody plants and woodland perennials, which surrounds a bacterial dominant area of double-dug beds for intensive annual (and field perennial) production. The forest, which will grow in fertility, is uphill from the bacterial area, so that nitrogen naturally washes down to the annuals.

    From a Permaculture perspective, I suspect that this is very worth doing, since it's quite easy and it's yet another small step you can take, but all the steps add up.
     
    Tristan Vitali
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    To be honest, the question sort of answers itself. You're asking about guilds, and guilds are formed with plants that do well together - if they do well together, they must have similar soil preferences. This is exaggerated in some instances, such as growing blueberries under your stands of pine trees, while more subtle in others where comfrey is growing under a peach tree. Fruit trees, from what I've read and heard, actually prefer edge and savanna type ecosystems because they like a mix of the two (fungal & bacterial). The fruit trees themselves sort of prefer more weight on the fungal side of things, while the clovers prefer more bacterial, but clover doesn't generally grow that well in purely bacterial nor fruit trees in purely fungal (not that anything in nature is "pure"). The thing to keep in mind would be where in nature these species grow, then try to mimic that in placement within your design - clovers aren't often close up around the trunk of trees (they stay out near the drip line where they get more sun), but a clump of aronia might be!

    I'd think the best bet is to design with gradations in mind, a wide overlap zone from fungal dominance to bacterial. Edges everywhere you can make them is sort of a rule of thumb, so most designs already prevent the "manicured lawn" sort of bacterial soil out of hand. The one place where most of us will have an extreme is within the denser, shadier parts of a maturing food forest - not the place for fruit trees anyway

    I like to think of it this way, rightly or wrongly - purely bacterial soil is "half dead", as is a purely fungal soil. There's really not a "pure" one way or the other, but we probably don't want to try for it either.
     
    Andrew Schreiber
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    Since soils either tend towards bacteria dominant, fungal dominant, or a blend of the two, does it make sense to try to make guild polycultures of plants that require different types of soils? In other words, would your fruit tree and your woody shrubs prefer fungal soil but your ground covers and herbaceous layer prefer bacterial? Are you compromising the health of some of your plants if you settle for a blend?


    Not at all. However, nature will tell you what works and what doesn't work.

    I have found that most herbs are tolerant of either type of soil, so long as the pH and Moisture content are suitable for them.

    My understanding that fungal dominated soil communities arise out of two dynamics associated with communities of woody plants.

    1. White-rot fungi are better at breaking down Lignin (woody material) than bacteria. Where woody mulch/inputs prevails, fungi will tend to be a primary decomposer.
    2. Woody plant communities tend to have a much more carbon rich soil, where nutrients are more dispersed. Fungi can transport themselves WAY FASTER than bacteria. Soils that are bacterially dominant tend to to be more nutrient dense around the root zones of plants, because the bacteria can't move through the soil as fast. i.e. They require worms/insects to help transport them.

    Also, there are lots of fungi that form endomycorhizal associations with grass/forbs which are commonly understood to live in bacteria dominant soils. Fungi are everywhere, even in soils where theoretically decomposition is primarily a bacterial affair. There are lots of different kinds of fungi. What I believe is meant when people say a soil is Fungi or Bacteria dominant is really a question of "what is the mulch like" which effects the the primary decomposer in the system.

    woody mulch > tends toward fungi, as they can create the enzyme lignase and break wood down.
    cellulosic mulch > tends toward bacteria who can readily create the enzyme cellulase and quickly break down that material.
     
    Paul Cereghino
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    What I find interesting about the thread is the struggle to shift from conceptual model, developed through observation into a predictive model for management. It is so messy, and is in my mind a metaphor for the challenge of implementing permaculture principles (or any biomimicry for that matter).

    Soils differ in populations of decomposers
    I have a fruit tree. I place woody mulch. The tree "does better"
    Therefore I conclude:
    I have modified the soil decomposer population and that is affecting tree heath?

    There could be 10 other logic chains explaining a change in tree health, since woody mulch is also a disturbance (suppressing other competing individuals and functional groups) and a nutrient source (albeit after a lag), and has physical properties (soil moisture retention), and each fruit tree species may have different relationship with microbial communities, and microbial community, and the fruit trees relationship are likely mediated by climate and geology (in a naturally P rich soil, maybe trees are less dependent on fungal foraging and delivery?)

    And so as far as I can tell we are left with a more general theories that:
    1) importing (or growing for chop and drop) woody mulch usually benefits those species not buried under it through multiple mechanisms...
    2) accumulation of carbon reserves in soils are generally good for evening out climate fluctuations and increasing nutrient cycling to improve growth of all individuals of a "competitor" inclination (read Grimes for more)... and
    3) As you shift from an initial disturbances to system development you inevitably move from bacterial to fungal systems, and maintenance of bacterial systems = disruption of fungal systems and requires disturbance...
    4) And that importing carbon, and creating disturbances both require work which burns energy, which needs to be evaluated at the appropriate scale.
     
    Andrew Schreiber
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    Well said Paul.

    While I have abstract knowledge about soil biology, I can speak mostly from practical experience that woody perennial systems tend to have more of an obvious presence of fungi than openfield/pasture systems.

    The addition of rough woody mulch on trees/shrubs has a beneficial effect. And as you wrote, that is likely for a variety of reasons.

    I have not worried too much about what the existing biology of soil is where I am planting. So long as there is intacted healthy soil food web, the soil theoretically develops it's own equilibrium naturally, as a response to the altered conditions.

    a few simple tactic I have used when planting out tree in open fields (presumably places with a minor fungal base it to both:
    1. incorporate biomass into the tree planting hole (small scale hugelkultur), and
    2. innoculate the hole with native forest soil (bring in a variety of fungi that can immediately start working in the system)
    3. mulch with rough woody biomass (to deter deer, retain moisture and suppress aggressive grasses)

    Theoretically these practices help establish an island of fungal based soils in the root zone of the trees. But I reckon that this is merely a way to speed up a process of colonization which would happen eventually anyway.
     
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