UKTC Archive

RE: Soil Bulk Densities

Subject: RE: Soil Bulk Densities
From: Adrian Lamont
Date: Aug 11 2014 01:36:39
Hi,

James Urban gives maximum attainable density for sandy loam of between 1.85 
and 2.05 gm/cc, so your readings are high but certainly possible, according 
to that.  Table 4.1 of Roots in the Built Environment is based on forest 
soils so maybe those values are lower than in a typical urban soil.  Fig 4.4 
shows the results of a study that indicated soil density was increased by 
approx. 50% on construction sites, where compaction was accidental.

It seems to me the tests you have done and the existing research justify 
remedial measures.  The alternative is to wait until the tree starts to show 
symptoms (which won't be proof of the cause) and remediate then.  What you 
decide to do depends on the rights and wrongs of it and the value of the 
trees, but if I held the whip hand in that situation I would be asking for 
decompaction measures.  That's not passing the buck Jim, in fact I see it as 
the opposite - making a decision based on the available information.

Regards

Adrian Lamont
Arboricultural and Landscape Advisor
Local & Sports Parks (South)
Ph 09 262 5183 | Fax 09 262 5414
Auckland Council, Kotuku House (Level 3), Manukau Square, Manukau City, 
PB92300, Auckland 1142
Visit our website: www.aucklandcouncil.govt.nz

-----Original Message-----
From: Jim Quaife [mailto:jq@xxxxxxxxxxxxxxxxx.co.uk]
Sent: Friday, 8 August 2014 6:42 p.m.
To: UK Tree Care
Subject: RE: Soil Bulk Densities

David, you don't say the soil type or species.  What is it about the 
professional test results you don't believe?   Have you phoned the soil 
tester to ask?
We know that compaction is injurious to tree roots, and there are views 
published which say that the first pass of a wheel will cause irreparable 
damage.  The tricky thing is that it will depend to an extent on how the 
machine was used - have you contacted the manufacturers to ask what the 
ground loading is?  Was the machine just driving in a straight line over the 
root system or was it slewing?  100mm is a shallow skim and the machine will 
have been stationary when the bucket was in action.
We are very happy to jump onto perceived knowledge but it has to be in 
context.  With the greatest respect Adrian, the job of a consultant is not to 
pass the buck, but to resolve the matter.
The difficulty is that I am sure we have all seen numerous examples of what 
appears to be outrageous soil disturbance and compaction, and yes the 
subsequent demise of a tree, but also instances of no ill-effects at all and 
driving past years later seeing the trees flourishing.
The bottom line is, are you to recommending de-compaction because a text book 
says so, or because it is necessary?
Please don't misinterpret this as me saying whether you are right or wrong, 
and I'm not saying that machines can be used over root systems with impunity 
- it is just an example of where the mindset should be objective.
Jim

-----Original Message-----
From: David Bailey [mailto:oldoaktree@xxxxxxxxx.net]
Sent: 07 August 2014 21:45
To: UK Tree Care
Subject: Soil Bulk Densities

Some collective wisdom may help me here, and I will thank you for it now!



I am acting for a client who has bulldozed a site and now needs to make 
repairs to the root zones of significant trees that have had approx 100mm of 
soil graded off. It was immediately mulched after I was given instruction.



I know the site very well and the ground used to be a grassed lawn which no 
vehicle could get to.  The offending vehicle was a 15 tonne 360 excavator.




I requested an engineer carry out a soil Bulk Density test to find out how 
compacted the soil was. This came back as 1.90 Mg/m2 which is rather high 
when compared to table 4.1 in Tree Roots in the Built Environment which gives 
undisturbed soil a value of 1.07 and heavily compacted soil 1.33 Mg/m2. The 
soil is a sandy loam.



I got a second test back at 1.59 Mg/m2 which again seems very high. Now this 
isn't my usual line of work, but do you think that maybe these two readings 
of 1.90 and 1.59 might be anomalies and I need a few more tests or do you 
think I should just dive in and suggest a bit of Air spade de-compaction.
Any advice on that one well received also!



Cheers



Dave



David Bailey

Old Oak Tree Care

BSc.(hons.) M.Arbor.A, cert. Arb. (RFS)

01630 XXXXXX

07813 XXXXXX







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