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Subject:

Re: Oak and Hazel charcoal

From:

"Asouti, Eleni" <[log in to unmask]>

Reply-To:

The archaeobotany mailing list <[log in to unmask]>, Asouti, Eleni

Date:

Thu, 26 May 2016 15:53:11 +0000

Content-Type:

text/plain

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Dear Mike et al.



Good question, but before considering anything else, it might be worth considering the context(s) in which your charcoals originated. If you have a lot of oak (or predominantly oak) then this surely means that oak was the most commonly used fuel wood, which tallies nicely with Dana’s observations. 



Now whether or not these samples are representative of the full range of taxa managed for fuel would also be dependent on the number of fragments examined from each sampled context, the spatial distribution/coverage of sampling, the range and types of sampled contexts, etc. In other words, you may be dealing with a fuel collection regime whereby most of the fuel used was oak, and where registering the presence of other taxa is largely dependent on the breadth and accuracy of your sampling and subsampling strategy.



I think we can safely assume though that the most frequently used fuel taxon was oak, there seems to be little doubt about this, and (any) burning and/or mass reduction biases have little relevance in this respect. Perhaps a way to gauge the presence of other taxa would be to select a context or two containing dispersed charcoals (i.e. materials derived from secondary contexts, i.e. fuel waste disposal area used over a period of time, something like a midden layer) and examine a significant number of >4mm charcoals from it (take it up to 300-400 fragments if time and resources permit). If you still find just oak then you would simply get confirmation that hazel (if present nearby and readily available) was probably reserved for other purposes and not used as fuel.



Another thing you could try is to scan samples for macroscopically identifiable twigs and other plant parts, (hazel nuts I think has been already suggested). Perhaps you can try the above mentioned subsampling strategy on samples that have produced hazel nutshell, and see what results you get.



Hope this helps,



All the best,

Eleni









________________________________________

Dr. Eleni Asouti

Senior Lecturer in Environmental Archaeology

Director of Postgraduate Research

Department of Archaeology, Classics and Egyptology,

University of Liverpool

12-14 Abercromby Square

Liverpool L69 7WZ, UK



Tel: (+44) 151 79 45284

E-mail: [log in to unmask]

http://www.liv.ac.uk/archaeology-classics-and-egyptology/staff/eleni-asouti/







On 19/05/2016, 11:11, "The archaeobotany mailing list on behalf of Dana Challinor" <[log in to unmask] on behalf of [log in to unmask]> wrote:



>Hi Mike,

>

>Just a few thoughts to add to the discussion:

>

>1. I think there is always some element of bias or selection in fuelwood choices.  Charcoal assemblages never include the full potential range of burnable taxa.

>

>2. Why would assemblages from non-funerary cairns not be subject to some selection?  What activities do they think are represented?  Mixed domestic waste?  Presumably not clearance.  Unspecified industrial?

>

>3. The model for South Devon (based on pollen) suggests large-scale clearance episodes had occurred by the mid-late Bronze Age (roughly speaking, depending on where exactly your sites are) - see 

>Straker, V., Brown, A., Fyfe, R., Jones J. & Wilkinson, K. 2007a. Later Bronze Age and Iron Age Environmental background, in C.J. Webster (ed.), The Archaeology of South West England,  South West Archaeological Research Framework, Resource Assessment and Research Agenda Somerset County Council, Taunton, 103-116 

>

>Of course, some woodland persisted on sheltered hillslopes etc, but perhaps hazel was specifically reserved as a food source rather than used for fuel. And any management of woodland is in itself a selective practice.

>

>4. When you say there is more oak, is this on quantity?  - since oak fragments more than hazel, this is an intrinsic bias.  What about the character of the wood used - as Robyn says, smaller diameter material used for kindling is more likely to burn to ash.

>

>5. Do you have any charred hazelnut shells to support the pollen evidence for hazel and highlight the absence of hazel wood?

>

>Finally, from my experience of working on prehistoric charcoal from the south-west region, generally - oak is almost always dominant  (in frequency and quantity), with significantly less hazel (and mere traces of heathland) - by the RB period, there is significantly more Ulex/Cytisus, more scrub/hedgerow types and still a fair amount of oak - with hazel only the 3rd most frequent (or less) taxon.  I think the key here is context and understanding selection/management practices.

>

>All the best,

>Dana

>

>

>Dana Challinor, MA (Oxon), MSc

>Freelance Archaeobotanist: Wood and Charcoal

>University of Oxford: DPhil Candidate

>

>----- Original Message -----

>From: "Mike Allen" <[log in to unmask]>

>To: [log in to unmask]

>Sent: Thursday, 19 May, 2016 9:50:54 AM

>Subject: Re: Oak and Hazel charcoal

>

>

>

>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) 



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