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Interspecific root interactions

 
Adam Geriak
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Location: Cape Cod, zone 7a
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Hello Mr. Kourik. I have very many questions concerning roots. My particular area of interest is in inter-specific root interaction. How big of a role would you say that root to root competition plays a role in community development... or polyculture development? I understand that many factors play a role, and that the name of the game is fulfilling different niches, but how important is it to fulfill different root-zone niches/habits? Does it all come down to the roots habit (flat, heart, tap), or is there more to the picture than just the habit?

This is an area of extreme interest to me and I am thrilled that you've written a book on the topic.

Thanks!
 
Robert Kourik
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Hi Adam, All tree roots in the temperate zones are mostly near the surface - 50% or more in the top 12-18 inches. They all have to "duke it out" in the shallower soils. Only 2% of all trees have taproots, so depth is not the issue. I have a drawing where the apple roots of one tree seem to be growing away from another apple tree. This is confusing as prosperous apple orchards are all over the county I live in. I don't know of any case were different species of tree roots avoid each other. But there are plants with allelopathic chemicals that stunt the growth of other plants - examples include marigolds, walnut trees, elderberry stunts grasses, buckwheat stunts weeds. etc. See the list in my appendix.
 
Robert Kourik
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apple roots versus apple roots red is canopy/dripline
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[Thumbnail for Untitled.jpg]
 
Adam Geriak
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Location: Cape Cod, zone 7a
forest garden toxin-ectomy woodworking
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Thanks for your response!

So root to root competition is an important factor when considering community composition.

How about mutualism? Is there any cases where the roots from 2 different plant species mutually benefit off of eachother?

My interest here stems from a garden design lens. Can landscapes be designed to maximize root-root interactions?
 
Robert Kourik
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In most cases roots aren't mutually beneficial. But they can grow quite well together in the same aerobic layer of soil - the upper 1-2 feet. But legumes and legume trees do provide a small amount of nitrogen over the years. But most of the nitrogen goes into the tree, only a tiny bit is "shared" with other plants. The legumes as a group have to be shocked in order for the nodules to "shed" for the use of the nitrogen nodules by other plants - mowing, grazing, heavy pruning, fire, death.
 
Xisca Nicolas
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Location: La Palma (Canary island) Zone 11
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I still growl at some people when I see them water the trunk of a tree....
And even the "water at the crown" is nearly a myth!
So funny to see your drawing!

I believe in "water all the time at the same place".
Except when you want some roots to die by drying.

I read that plants share more in dry zones, that they swap nutrient and water.
It is supposed to work through something more subtle than the well know nitrogen system of legumes, through a network of fungies.... maybe also bacterias, this I do not know....
 
Steve Farmer
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Location: South Tenerife, Canary Islands (Spain)
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Robert in your drawing it looks like the roots are avoiding all three trees, but as the other apple tree s the closest tree, they seem to be growing away from the other apple tree. Would your pic look the same if the second apple tree and the cherry tree positions were swapped?
 
Xisca Nicolas
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Location: La Palma (Canary island) Zone 11
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Well my interpretation was not about avoiding anything,
but about looking for water.
This tree is just growing in the direction of the trees to get water from their drip line (the circles).

Its precise expantion between the tress certainly has to do as well with the slope.
The roots are where they can find the more water.
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