What does tree pruning do to the roots?

[Bundle 2]

I think that the relevant point is herein Pat....it eludes to the regrowth after the 1-2 yr cycle.

If you reread the thread Im confident that you will find your answer...

i guess you could do this even more incrementally if you wanted to. Essentially it depends on the tree species ( ie-how vigorous a species is it? )

Its a good idea. This done to mitigate the occurrence of heave.

Do you understand the difference?

not being funny....Its a good policy to adopt on clay soils (so called elastic/plastic )

[daltontrees]

I was a surveyor in a previous life and the taught wisdom on tree removal was that to prevent heave in shrinkable (and therefore expandable) clays the tree should be removed gradually. Any RICS expert standing up in court to try and defend his advice to do otherwise, advice that had resulted in either heave or continued subsidence, would possibly get massacred. If we are to believe the cited paper there is some ideal balance whereby so much crown could be removed in year one as not to stimulate rapid moisture uptake of the regfenerating tree but not so much as would let the clays rehydrate gradually and not cause heave.

 

After all that has been said in this thread I have absolutely no idea now what % should go in year one. %0% seems as good a guess as any.

 

In practice people talk about trees as if they 'think' but it's not like trees have a board meeting every now and again to agree how many roots or shoots are needed. The real answer may lie somewhere in an understanding of the hormonal mechanisms that regulate (stimulate or inhibit growth). Maybe pruning sets loose a bucket of hormones that cause roots (that otherwiswe are woody and fairly passive) to put out a mass of new temporary rootlets to feed the new leaf and shoot and callus growth? This would be compatible with woody roots not dying back.

 

I have read that a small amount of auxins in a growth tip will cause root or stem elongation but a large amount will inhibit it. Complicated.

 

I must lie down now....

[Frimsley]

Are we wrong then in view of the above facts to remove a large tree over two seasons when on shrinkable clay soil to reduce the possiblilty of any adverse movement?

 

Yes. If the soil is going to recover it's going to recover. It doesn't really matter how fast it recovers. All you do by recommending phased removal is prolong the home owner's agony.

[Bundle 2]

Yes. If the soil is going to recover it's going to recover. It doesn't really matter how fast it recovers. All you do by recommending phased removal is prolong the home owner's agony.

 

I see the logic of the point you make here..

I have made claims that differ to this and even whilst making them was aware of the a generlisation inplied by giving such an apparently emphatic answer.

I would still have thought a more gradual wetting , sorry, rewetting , of clay soils could only really be to the buildings benefit for precisely the reason of how quickly it occurs...?

Interesting. Thanks for posting...gonna dig alittle around this one!!

[Ruskins Trees]

On a slight tangent. I was told by an arb cons that Pruning will at some point restrict roots, otherwise ancient field hedges would have roots right across the field. Although he paraphrased it, "if you slap (prune) a hedge for long enough, it will enventually learn that it does not need a large root system".

[gibbon]

Won't it partly depend on how much stored energy the tree has? I would think if it had a lot of energy reserves it could maintain the roots for a while (with some loss of disposable fine roots) and try to recover its leaf area. If it was low on reserves it would not be able to recover leaf area so quickly and would not be able to support the roots while in recovery, so the roots would likely die back a bit.

Seems reasonable anyway, even if I just made it up

 

I'm thinking along similar lines. I would assume that reducing the canopy of a young or vigorous tree would maybe slow down the rate of root growth in the short term. There would be an temporary inbalance in the root/shoot ratio. Rapid shoot extention and I would assume that the rate of root growth would be a little slower until the natural ballance has been restored.

 

From my experience I have no doubt that a sever pruning of a over mature trees will lead to some root loss. I've often seen evidence of root decline on trees after large limbs have been lopped or removed, especially large diameter trees. Some trees develop distinct source/sink relationships between limbs or part of the canopy and large roots. If you remove a section of the canopy which is "feeding" a large root and the tree is not vigorous engough to replace the foilage surely the root is going to die back? .

 

Most likley one of those questions with to many variable for a clear answer. I guess it all depends on the extent of the pruning, and the age and species of the tree.

[patrickosborne]

I see the logic of the point you make here..

I have made claims that differ to this and even whilst making them was aware of the a generlisation inplied by giving such an apparently emphatic answer.

I would still have thought a more gradual wetting , sorry, rewetting , of clay soils could only really be to the buildings benefit for precisely the reason of how quickly it occurs...?

Interesting. Thanks for posting...gonna dig alittle around this one!!

 

Thanks for the info, this discussion is interesting, I have always made it my policy to remove a large tree over at least two seasons alowing the soil(not the roots) to adjust to less water uptake which must surely be the case with less photosynthesis taking place, BUT am I right in believing that OCA nearly always reccommend removal in one go wheather or not on clay soil ?

 

I believe this was the case when I worked for a local authority a few years back.

 

So although we tell the public the reasons for staged removal are they really sound ??

[nailer]

I was told by an arb cons that Pruning will at some point restrict roots, otherwise ancient field hedges would have roots right across the field. Although he paraphrased it, "if you slap (prune) a hedge for long enough, it will enventually learn that it does not need a large root system".

 

I prefer that example / analogy to the bonsai theory I mentioned earlier. Cheers.

 

Some great posts in this thread. Putting the shrinkable clay / subsidence issue to one side for a second, it seems like we kind of know the answer, but it is very hard to generalise for tree size, tree species and come up with a solid answer that is useful for our customers.

[Mesterh]

Surely in the way that bonsai grow, you restrict root growth to restrict, well in a sense shoot growth.

An vise versa.

[Bundle 2]

Thanks for the info, this discussion is interesting, I have always made it my policy to remove a large tree over at least two seasons alowing the soil(not the roots) to adjust to less water uptake which must surely be the case with less photosynthesis taking place, BUT am I right in believing that OCA nearly always reccommend removal in one go wheather or not on clay soil ?

 

I believe this was the case when I worked for a local authority a few years back.

 

So although we tell the public the reasons for staged removal are they really sound ??

 

 

Only if you get it right! You gonna want to know what right is...right?

It is less than a precise science, certainly to make a "generalised " claim that any given percentage reduction of canopy will reduce water uptake for X number of cycles/years,,,whatever.

OCA doc says , you are quite right mate, less than year "in most cases " .....So, that's what I mean about gettin' it right. How can you tell?

Season will affect SWD As will deciduous v conifer presumably....I aint no expert for damn sure. I guess I could derive ways of plotting SWD and so transpirational uptake(locally ) for a given tree. Thus get a handle on the trees optimum "removal" window...but I got to admit. It seems like a hell of a lot of hassle.

Several things strike me as pertinent with respect the rewetting of clays in relation to buildings...

Clay is soft..it certainly becomes softer as it is rehydrated..

If a building has accommodated a tree's root system during its growth...it indicates a degree of "flexibilty" within its structure( the building)....Why then are you flagging up heave, even if it did occur, as a problem neccessarily? ( I am aware that much has been built around trees and not the other way round, hence I suppose I favor the.." its not the tree, its your flimsy foundation and engineers failing to think it thru'" argument!!)

I think I would be looking to the the building for answers as to feasabilty and need for staged reduction. Foundations are an issue and I mean by the very nature of their engineering. In the same way, the materials used. I know less about buildings than I do about trees, so that should tell you it's a case of the blind leading the blind here mate...

Essentially....the science makes sense. ( Yippeeee!! )

The process would be less than straightforward and in any case involved, and ask yourself...can you prove a staged reduction worked jus' cos the building's fine? I dont know.

In conclusion I bodge the following ramshackle conclusions

 

It would be influenced by a significant number of variables; some we have noted, and others also.

ie...

Species

Age Class

Aspect

Drainage

Microclimatic factors (aspect +exposure+recent climate variation etc etc...?)

Building-age, recent history(incl surrounding area)

Engineering design ( foundations, surroundings)

Materials used

I m certain there may be others....

 

Here's the sciency bit... I guess I would want to see more than a fair few of these " factors" ticked in order to think that a staged reduction was an appropriate recommendation , if you could get it right anyway.

 

I guess I may be boring ya'..its good to think these things thru even if it is a load of ol' tosh!!

 

I think there are probably few situations wherein heave can be successfully avoided by tree pruning techniques and science.....?