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oak tree tarmaced around base


Matthew Storrs
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just a question really, yesterday i was walking through a carpark and saw a large mature oak tree in apparent good heatlth etc but it was tarmaced right up to the base, anyway i was asked by present company how it got enough water, then realised i didn,t really have a good reply, any answers? oh yes and the tarmac stretched far beyond the extent of the roots if you know what i mean!

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The tarmac will be porous. there will be run off during a down pour, but some of that water will seep in & through to the root zone.

 

David,

Wouldn't the tarmac after same time be clotted with and compacted by sand, salt and other fine materials and loose it's porous and rain seeping in & through character ?

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For what its worth my experience has been that as David suggests bitumen (whilst it is definately not recommended surface treatment for tree health) is at the end of a list of construction issues that car park trees have to contend with and survive as best they can. It is not totally impermeable this is one (yes there are numerous others) reason why resurfacing programmes have a relatively short turn around period.

 

It is also really important when considering how mature trees move water to recognise that direct surface perculation is not always the biggest factor in determining relative soil moisture through the subterranean profiles. Trees (particularly mature trees) move water vertically and horizontally, rehydrating soil volumes in tune with their own biological cycle (when relative soil moistures permit it that is).

 

Unless catastrophic root damage has occurred we have seen mature trees (75-150yr old trees in suburban Oz) continue to persist for almost a decade after the construction blight occurs.

 

When asked to assess car park trees it is critical to be able to understand what civil works went on (cut, fill, compaction etc..) and just how much of the subgrade has been 'transformed'...without that knowledge it is almost impossible to sensibly advise what the future might be for the tree concerned.

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that bitumen (whilst it is definately not recommended surface treatment for tree health) is at the end of a list of construction issues that car park trees have to contend with and survive as best they can. It is not totally impermeable this is one (yes there are numerous others) reason why resurfacing programmes have a relatively short turn around period.

It is also really important when considering how mature trees move water to recognise that direct surface perculation is not always the biggest factor in determining relative soil moisture through the subterranean profiles. Trees (particularly mature trees) move water vertically and horizontally, rehydrating soil volumes in tune with their own biological cycle (when relative soil moistures permit it that is).

Unless catastrophic root damage has occurred we have seen mature trees (75-150yr old trees in suburban Oz) continue to persist for almost a decade after the construction blight occurs.

When asked to assess car park trees it is critical to be able to understand what civil works went on (cut, fill, compaction etc..) and just how much of the subgrade has been 'transformed'...without that knowledge it is almost impossible to sensibly advise what the future might be for the tree concerned.

 

Sean,

Thanks for sharing, but I'm more concerned with a lack of oxygen, because mycorrhizal fungi need 20 % more than fine tree roots and root hairs, than a lack of moisture or water, as the reallocation of moisture and rehydrating of the soil for the greater part takes place via the hyphae and mycelia of the mycorrhizal symbionts.

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I was told by a man infinitely more clever than I shall ever be (Les Round), that trees capture 30% of rainfall though stem runoff - i.e. the water reaches tree roots by running straight down the branches and stem and in to the ground.

 

Unless the tarmac was silicone sealed around the base of the tree, the tree can still get some decent water via rainfall.

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I was told by a man infinitely more clever than I shall ever be (Les Round), that trees capture 30% of rainfall though stem runoff - i.e. the water reaches tree roots by running straight down the branches and stem and in to the ground. Unless the tarmac was silicone sealed around the base of the tree, the tree can still get some decent water via rainfall.

 

Paul,

This is only true for tree species with a relatively open canapy and not for tree species, such as beech, with leaves that transport rain towards the dripping zone of the outer crown projection.

Besides, that's not where most of the mycorrhized fine roots are responsible for transporting the moisture to and dividing it over the total root system of the tree.

Edited by Fungus
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Paul,

This is only true for tree species with a relatively open canapy and not for tree species, such as beech, with leaves that transport rain towards the dripping zone of the outer crown projection.

Besides, that's not where most of the mycorrhized fine roots are responsible for transporting the moisture to and dividing it over the total root system of the tree.

 

That makes sense.

 

I would think that the bark surface would have a big effect too - smooth barked trees losing water quicker that trees with deep ridges.

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I would think that the bark surface would have a big effect too - smooth barked trees losing water quicker that trees with deep ridges.

 

True, and the compensatory capability of trees, such as beech and Acer, to form water "containers" (see photo) from "strangulation roots" at the side of the tree where roots have died or have no access to water because of compaction of the soil.

Also see my Beech & Laccaria amethystina thread.

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59765ec19493b_1.Beukreservoirstamvoet.jpg.f60b7765e6549bcf736eabc9e1f49d5c.jpg

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Sean,

Thanks for sharing, but I'm more concerned with a lack of oxygen, because mycorrhizal fungi need 20 % more than fine tree roots and root hairs, than a lack of moisture or water, as the reallocation of moisture and rehydrating of the soil for the greater part takes place via the hyphae and mycelia of the mycorrhizal symbionts.

 

Absolutely true oxygen and the presence of pore space (macro and micro very very important...hence the relevance of having some idea of how the subgrade has been changed. Not all pavements are formed on the same foundation..(I know you know this).

 

Your point about the mycorrhizal fungi needing 20 % more than fine tree roots and root hairs is something I have not heard before (certainly not quantified like that) are there any papers you can think of that make mention of this please, I would certainly like to increase the weight of evidence presented in certain real situations where trees are threatened by such construction.

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