4.3 Archaeobotany

Archaeobotany as part of the archaeological study of sites generally falls into the category of using plant macrofossils to reconstruct economic and dietary information from sites. Charcoal fragments and occasionally wood, may also be identified to look at which arboreal species were used for fuel and construction materials. Commonly archaeobotanical materials are also identified as a necessary preparation for use in ¹⁴C dating.

Plant macrofossils

Charred grain before and after sorting of a flotation sample into species, including here oats, barley and wheats, together with wild taxa.

The most common from of plant macrofossil study on archaeological sites is looking at charred plant remains, generally charred cereal grains and nutshell remains. Samples are usually collected through a bulk sampling strategy from negative features encountered on the site (e.g. pits, postholes, slot trenches). Strategies may include the specific targeting of some features such as corn-drying kilns, hearths and pits where charred grain can often be found in abundance. Other times strategies may be more ad hoc and up to the discretion of the on-site archaeologist. In ideal circumstances site strategies would be established in collaboration with an archaeobotanist prior to excavation commencing with regular site visits by the archaeobotanist during the excavation itself.

Bulk samples taken from site are generally processed using the flotation method (cf. Kenward et al.1984) with the sample then refined into two (retent and flot) categories. Archaeobotanical material will then be sorted by the archaeobotanist (flot sample) together with (where applicable) a sampling processing team (retent sample). This process then requires that the team are trained to recognise (though not necessarily identify) charred plant material, which can then be further examined by the archaeobotanist. Depending on the project itself the charred plant material may be merely assessed for preservation, variety and abundance or the material may undergo full analysis. Often a mixture of the two is employed, though ideally an assessment phase should be done as standard and analysis wherever (funds allowing) possible.

In Scotland the main area of study involving plant macrofossils has been the study of charred cereal grain. The reason for this is two-fold: firstly charred plant remains are the most likely plant material to be preserved on archaeological sites and secondly the expansion in the number of archaeological units across Scotland coupled with, until recently, the boom in development has meant more studies have taken place. Charred cereal grains are often taken to assessment level on archaeological sites with full analysis rare. The focus of the cereal grain work is often to build a picture of the crops that were grown during the time period of the particular site and to relate this to subsistence life styles or cultivation for trade and as a landuse. Often little is said about the grain beyond the confines of the site itself and thus there is an opportunity to begin linking individual sites to emerging wider [national] pictures (e.g. Neolithic cultivation – see below).

The charred weed seed assemblages often get little attention, with reporting and discussions focusing more on grain. This can represent a loss of important information as weed seeds or non-cereal plant remains can represent a number of activities on site for example; turves used as fuels, construction materials in structures and kilns together with providing data on harvesting techniques and field conditions (poor drainage etc.). This lack of attention may come from only assessment work having been carried out on sites and these remains not, perhaps, being considered suitable for ¹⁴C dating. Charred wild taxa such as apple pips and hazel nutshell are more commonly identified from sites with hazel nutshells in particular being prominent (e.g. McComb and Simpson 1999) allowing comment on the gathering and use of wild foodstuffs. In more urban locations and in particularly from medieval contexts, charred (and waterlogged) plant macrofossils may be studied to not only look at evidence for economy and diet but also in connection with the trade of exotic plants such as walnuts, figs and grapes.

Charred fruit stones – This sample was taken from an isolated pit at Powmyre Quarry, Strathmore, Angus. All of the other pits at the site were prehistoric, however, this sample containing fruit stones of plums, blackthorn and wild cherry, together with apple pips and hazel nuts is likely to be medieval in age. © Scott Timpany

Charcoal and WoodWhere waterlogged sediments are present on sites, such as peats and silts, plant macrofossil assessment/analysis may be undertaken on non-charred plant material. Archaeobotanical studies on such material are often to do with palaeovegetational reconstruction of former environments, which are often carried out to support other proxies such as pollen and/or insect analysis as part of a multi-proxy approach. To date such studies of waterlogged plant remains are fairly sparse in comparison to the wealth of pollen studies that have been carried out across Scotland. However, plant macrofossils offer an increased possibility of comparing the wider vegetational communities signalled in the pollen record to what was growing locally (e.g. field layer) and also comparing these with modern analogues (e.g. Rodwell 2000). Combining the pollen with the plant macrofossil record gives an increased chance of linking pollen-types to species. Another, and growing use of waterlogged plant remains is to establish a further link in with proxy climate data. This usually involves the identification of mosses (e.g. Sphagnum) from raised bog sequences  and may be used in conjunction with testate amoebae and/or tephra studies.

Charcoal studies from archaeological sites in Scotland, to date, have generally been focused on the identification of fragments to tree-type. This is largely done in respect of the essential identifying material for ¹⁴C dating on sites and thus there are plenty of examples of publications where the only mention of charcoal fragments is as an id for dating. Where charcoal fragments have been identified it is usually as a fraction of the sample (e.g. 20-100 fragments) to investigate which arboreal species where used for fuel or possible construction material and then to link this back to the woodland, which would have been present during the period of activity. Regular features on archaeological sites where charcoal fragments are identified include burnt mounds, domestic hearths, pits and kilns (grain and metal working). However, charcoal fragments offer much more information than can be gained just through identifications, with further anthracological data available such as through the morphology of fragments, ring curvature and the presence of fungal material.

Waterlogged wood may also be present on archaeological sites where suitable deposits are present (e.g. peats). Studies on waterlogged wood range from looking at large timbers and tree remains (e.g. pine stumps) to small wood fragments identified with plant macrofossils during studies related to palaeovegetational reconstruction. Studies on timbers can come from construction materials such as from crannog sites together with archaeological objects e.g. stakes and barrel-parts (e.g. Jones et al. 2007) where tool mark, wood identification and dendrochronological analysis may be undertaken. More natural wood remains such as the remnants of former woodlands have also been examined in Scotland (Tipping et al. 2008a) in order to reconstruct former woodland environments, build chronologies and investigate the character and openness of such wooded environments. However, despite the strong presence of buried tree remains such as pine stumps across Scotland such studies are still fairly sparse and again are more likely to take place during multi-proxy studies (e.g. Tipping et al. 2008).

Practitioners and archaeobotanical reference collections in Scotland

These are few but mention can be made of the Dickson Laboratory at Northlight Heritage’s Bioarchaeology Unit in Glasgow, and at Headland Archaeology.

Looking towards the future

Plant macrofossils

1. Particular targeting of features such as Neolithic pits in order to look at why these features seemed to have been used so frequently to store/contain charred cereal grain
2. Neolithic agriculture: charred cereal grain and its chronological distribution. Maps could be made in an attempt to identify where agriculture began in Scotland, how this spread, where it spread from and any trends in crop use. To date this has happened sporadically with archaeobotanist’s on occasion collating data and with recent academic interest (such as Rosie Bishop’s post-graduate work, Bishop et al. 2009). This process could also be undertaken for other periods in Scotland.
3. Recent research has shown that charred grain have the potential to inform of climatic episodes such as periods of increased wetness and dryness. This information can be applied to agricultural sites and help us to understand some of the challenges people in the past faced together with helping to build more regional rather than national climate records. An area where this may be particularly useful is prehistoric farming in isolated/marginal locations and in corn-drying kiln studies. Such information could be linked to dendrochronological, tephra and testate amoebae studies.
4. More research into the weed seeds collected from sites may increase our understanding of the different farming (cultivation, harvesting and processing) methods employed throughout history and prehistory. It would be interesting to compare the taxa found from marginal locations with those from more central locations. This information could then be contrasted and compared with the arable weed assemblages identified in the pollen records.

Charcoal/Wood

1. More could still be achieved looking at the buried tree remains such as pine stumps across Scotland, both from an ecological point of view seeking what the root systems tell about soil conditions and how tree morphology can inform current research of woodland composition/openness. Can periods of poor growth be linked to phases of wet climate? Can tree-rings add to the dendrochronological sequences being developed to aid in the formation of a master chronology of pine in Scotland?
2. Charcoal fragments can be examined for more than just identification to family/species identification. More can be done with charcoal morphology in particular looking at the rings for curvature information and possible periods of cyclic cutting. This can reveal potential woodland management and be tied to pollen records etc. This would be of particular interest with features such as burnt mounds, smithing kilns and potential construction material.