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Thank you for that - very useful, especially helpful.

I often have hazel and charcoal in assemblages and the charcoal we have
from our South Devon sites is interesting in the lack of hazel in view of
its high preponderance in the local pollen spectra. Selection is something
we have considered, but burning is small BA firing events where elsewhere
in the region we have a good spectra of the local woods (ie we would expect
both hazel and oak). The archaeologists feels that these burning events
(associated with non-funerary cairns) parallel other BA general firing
(rather then specific kilns/ovens) and they cant see a reason for specific
selection. Other features elsewhere have much more defined and purposeful
firing pits where indeed control of fire and heat and selection of wood
(oak) is represented in the charcoal.

My unscientific bonfire observations (7 records) of burning wood from 1.7cm
to 12cm diameter, has show hazel and birch to be preserved less well in
charcoal lumps in the resultant fire, but oak (and beech) to be more common
as charcoal - and these are disproportionate to the wood proportions burnt
on the fire. The fine ash is unidentifiable, but the small whitened fragile
charcoal lumps (ie nearly ashed)  were predominantly (76%) birch and hazel
as opposed to oak and beech (excluding other garden bush and pyracantha
etc.)

Mike

On 19 May 2016 at 08:17, Robyn Veal <[log in to unmask]> wrote:

> Dear Mike,
>
> Thank you for an interesting question. I would suggest most charcoal
> specialists' experience in the lab is that hazel is not much weaker than
> oak (as charcoal).  The concept of ‘higher temperature burning oak’ vs
> ‘lower temperature hazel’ is somewhat confusing.  You possibly mean
> calorific potential (heat value inside the wood), which is slightly higher
> for oak than hazel (only slightly), a proxy for this is density.  A fire
> burns at a range of temperatures, depending on position in the flame, and
> contact with air, ash present and other factors, (particularly structural,
> as well as how dry the wood is), and but all the wood in say the central
> part of a fire will reach roughly the same temperature, regardless of the
> CP of any woods present. That your hazel is not preserved will be something
> to do with its condition beforehand (for example, relative dryness, size of
> branch).  Bigger branches take longer to dry out, and longer to ignite and
> burn.  Also the structure of oak is more ‘closed’ than that of hazel (but
> again, not by much).  Smaller branches have more of their wood in contact
> with the fire, and therefore greater ignition surface, greater contact with
> oxygen, and once a fire reaches a good temperature, smaller branches, (most
> other things being equal), burn faster, and more to completion.
>
> Eleni Asouti’s Charcoal analysis web has a good overview of charcoal
> preservation    pcwww.liv.ac.uk/~easouti/
>
> Other things of interest are books on fire and how it behaves - e.g. Fire
> on Earth, an Introduction, 2014 ( A Scott et al), and a good chapter by
> Dehaan, J, ‘Fire and Bodies’ in The Analysis of Burned Human Remains 2008
> (ed by Schmidt, C and Symes, S).  Deehan is a forensics expert who explains
> exactly how fire behaves in every aspect (the human remains part is
> incidental, this is also a very good book in general).
>
> We do very often see oak and hazel mixed together in many UK and European
> archaeological deposits. Of course we all know oak is the commonest taxon
> in the UK, but your note reminds us that representation in the archaeology
> is another thing; as for pollen, the % of wood taxa in archaeological
> charcoal doesn’t represent that originally present, nor necessarily the
> relative proportions of those fuels in the forest. Much has been written
> about this!
>
> For an English source, Phil Austin at UCL has carried out a lot of local
> experimental burning of fires mixed woods under controlled conditions, and
> you may like to contact him for more info.
>
> And - it could just be selection!
>
>
> Regards, Robyn.
>
> Dr Robyn Veal
> [log in to unmask]
>
> Affiliate researcher,
> McDonald Institute for Archaeological Research, Department of Archaeology,
> Fellow and tutor, Hughes Hall
> University of Cambridge.
>
> Honorary research associate, University of Sydney
>
> www.robynveal.com
>
>
> On 18 May 2016, at 9:20 pm, Mike Allen <[log in to unmask]> wrote:
>
>
> I have sites with open oak and hazel woodland in the pollen on a current
> upland heath. The charcoal from non domestic and non funerary and no
> industrial activity is nearly all oak? Where is the hazel? We have ne
> reason to thing that this is 100% selection
>
> Could the high temperature burning oak, mixed with hazel in a fire results
> on oak charcoal, but just hazel ash (that what happens on my bonfires)?
>
> Mike
>
>
> --
> Dr Michael J Allen, MCIfA, FLS, FSA
> AEA: Allen Environmental Archaeology
> Tel. 07828 103454    website at www.themolluscs.com
>
> and Visiting Research Fellow in Environmental Archaeology, Bournemouth
> University
> Series Editor: Prehistoric Society Research Papers (
> http://www.prehistoricsociety.org/)
> Series Editor: Oxbow - Studying Scientific Archaeology
> Vice President: Conchological Society of Great Britain & Ireland (
> http://www.conchsoc.org/)
> CSCS card holder (CRO)
>
>
>
>
>
>
>


-- 
Dr Michael J Allen, MCIfA, FLS, FSA
AEA: Allen Environmental Archaeology
Tel. 07828 103454    website at www.themolluscs.com

and Visiting Research Fellow in Environmental Archaeology, Bournemouth
University
Series Editor: Prehistoric Society Research Papers (
http://www.prehistoricsociety.org/)
Series Editor: Oxbow - Studying Scientific Archaeology
Vice President: Conchological Society of Great Britain & Ireland (
http://www.conchsoc.org/)
CSCS card holder (CRO)