Life on Songo Mnara: Kilimo, Bustani and the Ukame – Farming, Gardening and the Drought

Field of Sorghum on Songo Mnara

A Sorghum field on Songo Mnara. © H. McParland-Clarke 2013.

We stand, the hot sun beating down on us, surveying a field of sorghum (mtama). The harvest is late this year, M tells us that the crop is short and stunted because of the drought (ukame) and as a result, very little has been harvested, even this late in the season. Low rainfall during the rainy season has a major impact on agriculture on an island which has no fresh water for irrigation. Drought (Ukame) has affected the growth and yields of crops on the island for several years, exacerbated by soil exhaustion[1]. Local farmers cultivating pearl millet (uwele) and garden crops, including tomatoes (nyanya), experienced poor harvest and poor growth due to the lack of rainfall. Kilwa Kisiwani has a plentiful supply of fresh water, but on Songo Mnara local wells contain brackish water[1]. During our visit, we witnessed the construction of water reservoir tanks on Songo Mnara, installed by the World Monuments Fund to capture water during the rainy season to provide the island with fresh water during the dry season.

The road, Songo Mnara.  © S. Walshaw 2013.

The road, Songo Mnara. © S. Walshaw 2013.

We traversed sandy footpaths between sparse settlements, these roads, speckled with coral, guiding us through dense bush. The bush cleared, opening out onto a blackened clearing, a herd of cattle steered along their grazing route by a herder wielding a stick, on land subject to slash and burn. Once commonly used, slash and burn agricultural practices have been declining on the islands; traditionally sorghum (mtama), would be planted for three to five years, before being burned after the final harvest and left fallow for up to five years[1]. Though fishing (uvuvui) and agriculture (kilimo) form the main basis of the economy, families also graze small herds of cattle or goats in the bush and fields[1].  Farmers here don’t own the land they farm, only the crops they plant and the fences constructed to protect their crops; the land they farm is common land, owned by the community[1]. Land is passed on through ancestry and kinship and new farmers must consult the community before claiming land[1].

Cows amongst the ruins of Kilwa Kisiwani.

Cows amongst the ruins of Kilwa Kisiwani. © Hayley McParland-Clarke 2014.

We meet M, one of these new farmers, sitting on coconut palm mats outside the home he shares with his wife and children, chickens pecking at the dry sand. M tells us that they moved from the other side of the island to farm this land. Songo Mnara may not seem to be the most hospitable environment for agriculture, but M chose to move to his present location, as the soil – a fine reddish sandy loam – is good for cultivation, despite the large coral inclusions which are problematic. The fields are prepared for planting by cutting back bush and palm and burning the vegetation, adding valuable nutrients to the soil. Sorghum (Mtama) is sown after the first rainfall in December, to be harvested five months later in May. Much like other crops, including rice, only the seed head (inflorescence) is harvested, with the remainder of the plant, the stem and the leaves, left in the field, these will be burned the following December prior to cultivation. Aside from the nutrients added from slash and burn, the crops are not intentionally fertilised and are not irrigated, watered by rainfall only. The soil is not intentionally improved in any way, though M grows peas (ufuta) alongside the sorghum (mtama), this crop is low maintenance, and harvested simultaneously. The stalks of the plant remain in the field to be burned with the Sorghum stalks. This process is more than efficient intercropping, the burning of the plant stems following harvest of the peas in the field, likely releases large amounts of nitrogen into the soil, improving soil fertility. Though sorghum is particularly suited to harsh environments, the annual addition of nitrogen to the soil is likely to have a significant effect on the yield.

Papaya plantation, Songo Mnara. © Hayley McParland-Clarke 2013.

Papaya plantation, Songo Mnara. © Hayley McParland-Clarke 2013.

We moved on, Y led us away from the ruins of Songo Mnara, through the bush to his village, to his home of coral and daub, to meet his family and to show us his farm. Y did not sow any crops this year, as he was on the mainland so that his children could attend school, though his large papaya (papai) plantation was in fruit. Y told us that papaya was good to grow, as each tree lived for up to four years, producing a crop of up to 50 papaya (papai). The trees required very little management, receiving water during the rainy season (December-May), requiring no fertilisation and self-seeding, though up to 20 cuttings could be taken from a single tree for replanting. Y told us that papaya (papai) trees were an excellent investment. Three further papaya trees were grown in the toilet (choo) to the immediate rear of the house, rather than in the fields (shamba), for easy access, and presumably, good fertilisation!

Bananas growing in pockets of earth within the coral on Songo Mnara

Banana Trees growing in pockets of coral on Songo Mnara. © Hayley McParland-Clarke 2013.

Later, we joined R in a substantial plantation of bananas (ndizi), set in a small coral hollow filled with pockets of dark reddish-brown sandy loam. The hollow was high sided, with a narrow entrance through the rock, fenced off with logs to protect the plantation from bush pigs. Bananas (Ndizi) are planted in December at the start of the rainy season, each crop being transplanted from the previous crop, ready for harvest between May and July. During harvest, the trees are cut down, the fruit is removed in the field and taken back to the home, where some is stored, and some is sold at market. The trees remain in the plantation, drying, decomposing and entering the soil, providing the only fertilisation the crop receives. Y and R told us that their village was a good location for growing Banana and Millet, though they had experienced drought (ukame) and were unable to grow crops which required a lot of water, including Tomatoes (nyanya). More recently, farmers on Songo Mnara and Kilwa Kisiwani have moved away from traditional sorghum or millet cultivation, which although staples, are of little commercial value; instead, planting crops which will provide a staple in their diet and a cash crop for sale, including banana (ndizi), cassava (muhogo) and maize (mahindi)[1]. Households often cultivate small plots (bustani), growing a wide range of vegetables and fruits including tomatoes (nyanya), squash (malenge), pumpkins (maboga), okra (bamia), beans (maharage), lima beans (fiwi), peas (ufuta) and sweet potato (viazi vitamu)[1][2].Large scale cultivation often takes place in a more suitable location some distance from the home[1].

A bustani on Songo Mnara. © S. Walshaw 2013.

A bustani, a garden on Songo Mnara. © S. Walshaw 2013.

Though most farmers I met also cultivated rice, there is only one location on the island suitable, at Madaweni, a three hour walk from the Songo Mnara ruins. Farmers grow rice in a communal field, traversed by raised berms, embanked to separate the field from the adjacent salt flats and saline incursion[2].The fields are not irrigated and are fed only by rainfall[2]. This seems like a hostile environment to grow rice, but it’s important, rice is now a daily staple, but demand outstrips supply and so rice has to be imported for consumption[1]. The farmers select the best rice each year, to plant the following year, slowly adapting the rice to its unique environment[2]. The seed head (inflorescence) of the rice is harvested and stored in the home, whilst the leaves and stems remain in the fields[2]. .

Madaweni Rice Fields, Songo Mnara. © S. Walshaw 2013.

Madaweni Rice Fields, Songo Mnara. © S. Walshaw 2013.

Families live in field houses, constructed of Coconut palm leaves (Makuti), for up to three months a year, in order to protect and maintain the crops[1]. Crops must be weeded, but M tells me there are weeds which will affect the crops and weeds which will not. Only those which will affect the crops are removed.

A field house on Songo Mnara, viewed from the rear kitchen. © S. Walshaw 2013.

A field house on Songo Mnara, viewed from the rear kitchen. © S. Walshaw 2013.

Out in the fields ants are swarming over our feet, crawling up our legs, but M doesn’t even notice them. I try not to not to notice them too, my fear of harmless insects is a joke amongst the locals, who laugh at my very British fear of ants and bees. They’re used to them, ants are everywhere on the island. I ask each farmer we meet, whether there are insects which will damage the crops, but each time, they reply that there are no insects which worry them; though a recent UNESCO report identified disease and insect infestation as threats to rice and coconut crops on Kilwa Kisiwani and Songo Mnara[1]. All of the farmers are worried about bush pigs as they attack crops, biting at Banana (Ndizi) trees until they bleed and dehydrate to the point of death, eating the leaves of Sorghum or Millet.

Banana Trees fenced for protection on Kilwa Kisiwani. © Hayley McParland-Clarke 2013.

Banana trees fenced for protection on Kilwa Kisiwani. © Hayley McParland-Clarke 2013.

We walk back across the island, it’s getting dark and the paths will be hard to see, we take a shortcut across the beach to the east of the island and we meet the ladies who cook for us, walking home, carrying their belongings wrapped in kangas on their heads, laughing. This post presents a somewhat limited ethnography of farming (kilimo) on Songo Mnara. I interviewed several farmers on the island and they gave me a tour of their farms. Sarah Walshaw kindly conducted the interviews with the rice farmers. It’s important to note that all of the farmers interviewed accepted that the drought was problematic, but overall they were positive about their environment, it suited their needs and they saw it as good land for farming. They were proud of their land, their crops and their farming (kilimo) ability, and rightly so. Farming such a specific environment with water constraints requires crop adaptation and local knowledge, handed down from generation to generation. Limited land resources on an island are managed through common land and communal farming. Those who participated in the interviews were pleased to give me a tour and share their knowledge and I am grateful to them for doing so. The farmers I spoke to on Songo Mnara were pragmatic, and felt able to invest in their crops to produce a surplus for market. Names and details have been changed to protect the identity of the farmers and their families. Related Posts: From the Site Diary: Approaching Songo Mnara Day of Archaeology 2014 – Counting Phytoliths from Songo Mnara, Tanzania References: [1] Bacuez, P.J. 2009. Intangible Heritage, Tourism and Raising Awareness on Kilwa Kisiwani and Songo mnara. UNESCO office, Dar es Salaam, Tanzania. [2] Dr Sarah Walshaw (pers. comm.).  

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Ten things you might not know about Phytoliths

Christian Gottfried Ehrenberg Image © Wikimedia Commons File PSM V14 D570

Christian Gottfried Ehrenberg
Image © Wikimedia Commons File PSM V14 D570

1. Phytoliths were first discovered in Germany in the 19th Century

They were named by Christian Ehrenberg in 1835, who called them Phytolitharia, or ‘plant stones’ (Piperno 2006, 5).

2. If you’ve ever taken a Phytolith sample, you have something in common with Charles Darwin

Phytoliths were identified in dust samples taken by Charles Darwin from the deck of the HMS Beagle off the coast of West Africa in 1833. Darwin recorded sending these samples to Christian Ehrenberg who identified 34 types of phytolith (Darwin 1846, 28-29). Darwin was surprised that ‘a sample smaller than half a teaspoon’ contained seventeen different types of phytolith (Darwin 1846, 28-29).

3. Phytoliths are basically small fossil plant skeletons!

They form within some plants when they absorb Monosilicic acid (Si(OH)₄) from the ground water. The Monosilicic acid can become deposited as solid or opaline silica (SiO₂·nH₂O) within or between plant cells during transpiration, essentially producing a ‘negative’ of the cell within the plant (Piperno & Pearsall 1993; Piperno 2006, 6-8). Not all plants make phytoliths – some plants have cells with a genetic susceptibility to silicification, whereas other plants may make phytoliths in response to an environmental stress or effect, such as the over absorption of Monosilicic acid (Pearsall & Piperno 1993, 9; Piperno 2006, 8).

Articulated Pearl Millet (Pennisetum glaucum) Leaf Bilobate Phytoliths Image © H. McParland-Clarke 2015

Articulated Pearl Millet (Pennisetum glaucum) Leaf Bilobate Phytoliths
Image © H. McParland-Clarke 2015

4. No one really knows for sure why plants make phytoliths

It used to be thought that silica was deposited as a waste product within the plant, but it has been suggested that phytoliths provide support for plant structures, that they help plants to resist attack by insects or make them unpalatable for consumers (Piperno & Pearsall 1993; Piperno 1991).

5. Phytoliths are preserved in a wide range of environments

Due to their high silica content, Phytoliths are not dependent on charring, waterlogging or mineralisation like plant macrofossils, and their preservation isn’t dependent upon an anoxic environment, like pollen. Pretty simply, this means that if a phytolith producing plant has degraded somewhere, the chances of finding the phytoliths in any soil type are quite high. Phytoliths are particularly useful in tropical regions of the world where the preservation of pollen or plant macrofossils might be severely limited, leaving almost no information about plant use or environment (Piperno 2006, 151). But, like everything, there are more complex mechanisms which determine phytolith survival in the archaeological record, aside from pre- and post-depositional taphonomic factors, the degree of silicification of the phytolith – some will contain other elements which may make them more susceptible to dissolution (dissolving into the soil) – has a potential impact on its survivability and subsequent archaeological visibility (Piperno 2006, 21). Soil pH will also have an impact to some degree – higher pH values above pH 9 have the potential to increase phytolith dissolution. These conditions are relatively rare, occurring in high pH coral sediments, lime plastered floor surfaces, shell middens and within confined ashy layers (Karkanas et al. 2002; Piperno 2006, 22). Essentially, the take home message is that phytoliths will survive in most archaeological contexts, most of the time.

6. Phytoliths aren’t only produced in the reproductive structure of the plant.

Most of the evidence we see archaeobotanically is in the form of seeds preserved by charring or in some cases waterlogging or mineralisation. Whilst this has the potential to tell us about food preparation, consumption patterns and, to some extent, the local environment, the mode of preservation doesn’t provide us with the full picture. Because phytoliths can be produced in the leaves, stems, flowers and fruit of some species, it enables a wider range of applications. For example, at Çatalhöyük, the preservation is so pristine that baskets are outlined within the soil, formed of chains of white phytoliths visible to the naked eye and which can be identified to plant family. Baskets or matting made of reeds (Phragmites sp.) and rushes (Scirpus sp.) have been identified at Çatalhöyük, and in the case of the basket from within Building 5, the grass or reed basket identified by the presence of bilobates, was associated with Wheat husk phytoliths, strongly suggesting that these baskets were used for the storage of Wheat grain (Rosen 2005 206-207; Jenkins et al. 2012). In addition, the presence of Date Palm (Phoenix dactylifera) globular echinates, is doubly important – demonstrating the potential use of Date Palm basketry or cordage and the import or potential trade of an organic object during the Neolithic, as Date Palms were not native to the region (Rosen 2005, 207).

Phytoliths preserving the outline of a Basket in Building 5 Image ©  http://cnx.org/contents/335b3eeb-1ca4-4553-b93c-42ab830d4df4@1.1:4/Remixing_Çatalhöyük

Phytoliths preserving the outline of a Basket in Building 5
Image © http://cnx.org/contents/335b3eeb-1ca4-4553-b93c-42ab830d4df4@1.1:4/Remixing_Çatalhöyuk

7. Phytoliths are what is known as an in situ indicator

They are released during the decay of plant material and incorporated into soils and sediments during pedogenesis (soil formation). Unlike pollen, which can be designed to be wind or water dispersed to aid plant reproduction, phytoliths are relatively unlikely to travel long distances or become subject to wind dispersal. Therefore, it is often assumed that phytoliths are preserved in situ. Given that the dust from the HMS Beagle contained such a diversity of phytoliths, I’ll leave it up to you to decide whether this is strictly true. Though wind transport is possible, there are other things to worry about when interpreting a phytolith assemblage, including pre-depositional and post-depositional taphonomy. In other words, assuming that the phytoliths were not transported by the elements, there are a range of chemical, physical and anthropogenic actions which can impact their inclusion into the archaeological record. For example, post-depositional activities such as sweeping may remove the phytolith assemblage from domestic contexts (Malinsky-Buller et al. 2011; Rosen 2005). It’s important to remember that no archaeobotanical material is without these issues, and in secure contexts and discrete features where the archaeology is well preserved, the phytolith assemblage can be representative of plant use and activity areas.

8. Phytoliths can get stuck in your teeth!

Phytoliths have been found in the dental calculus of humans (Henry et al. 2010; Henry & Piperno 2008) and grazing animals (Gobetz & Bozarth 2001; Middleton & Rovner 1994). Phytoliths from the dental calculus of herbivores have provided an insight into the way in which the herbivores were managed during the American Colonial period in Virginia (Middleton & Rovner 1994). This approach combined with new approaches to the identification of livestock dung through soil geochemistry, phytolith and spherulite analysis has the potential to reveal important information about livestock management and the use of dung in domestic contexts (Lancelotti & Madella 2012). Phytoliths have also been found within dental calculus on the teeth of American Mastodons, providing an insight into their grazing habits during the Pleistocene (Gobetz & Bozarth 2001). The phytolith assemblage was dominated by grasses, with limited dicotyledon phytoliths from deciduous trees and Celtis sp. seeds (Hackberry) (Gobetz & Bozarth 2001). Did Mastodons have a sweet tooth?

The analysis of phytoliths from human dental calculus has revealed the probable consumption of Phoenix sp. (Date Palm) fruits among Near Eastern Neanderthal populations in Shanidar Cave, Iraq (Henry et al. 2010). However, starch is more likely to become occluded within dental calculus, the recovery of starch grains from dental calculus samples taken from human populations at Tell al-Raqā’i, Syria, outnumbered phytoliths almost 30:1 (Henry & Piperno 2008). Phytolith analysis of dental calculus can be a valuable tool when undertaken with starch analysis, but it seems that phytoliths are less likely to become occluded within calculus than phytoliths, which can lead to the necessary interpretation of an extremely small sample.

Articulated Sorghum (Sorghum bicolor) Husk Phytoliths Image © H. McParland-Clarke 2015

Articulated Sorghum (Sorghum bicolor) Husk Phytoliths
Image © H. McParland-Clarke 2015

9. Phytoliths have been found in Dinosaur poo!

Samples of Dinosaur coprolites produced by Late Cretaceous Titanosaur sauropods found in India revealed a surprise component of their diet, they ate grass! The teeth of Titanosaur sauropods or ‘the most prominent plant-eaters in Gondwana’ are not specifically adapted for grass grazing, yet phytoliths within their coprolites suggest that they consumed five varieties of grass (Prasad et al. 2005, 1178). The phytolith evidence revealed that they consumed palms, conifers and dicots in addition to grasses, suggesting that they had general grazing preferences, exploiting a wide range of taxa (Prasad et al. 2005, 1179).

10. Phytoliths are Spicy Stuff!

The, let’s say ‘universal’, preservation of phytoliths enables a greater understanding of aspects of food production and consumption which are often invisible. As their preservation doesn’t rely on charring and diagnostic phytoliths are not only produced in the seed part of the plant, phytoliths have the potential to be preserved within pottery residues, providing direct evidence of the use of plants, and to some extent consumption.

Phytoliths have the potential to illuminate aspects of a complex culinary process, which are largely archaeologically invisible. A recent analysis of late Mesolithic and early Neolithic pottery residues employed lipid, stable isotope, and starch and phytolith analysis revealing evidence of the use of Alliaria petiolata (Garlic Mustard) as a spice (Saul et al. 2013). The preservation of phytoliths within the pottery residues was good, with just over a third of carbonised pottery residues analysed containing phytoliths (Saul et al. 2013). The identification of Alliaria petiolata phytoliths demonstrates the use of a nutritionally poor food, selected for its taste, suggesting that prehistoric populations of the western Baltic consumed food with flavour, not only substance (Saul et al. 2013). This discovery was widely reported by the media including BBC News,  The Telegraph, The Independent, National Geographic and The Daily Mail. Addendum: However, the relatively small sample size and a focus on a single phytolith identification have been discussed in an interesting review of the paper in a blog post by Dr Lisa-Marie Shillito, who maintains Castles and Coprolites, a successful geoarchaeology blog.

References:

Gobetz, K.E. and Bozarth, S.R. 2001. Implications for Late Pleistocene Mastodon Diet from Opal Phytoliths in Tooth Calculus in Quaternary Research, Vol. 55, Issue 2. pp. 115-122.

Henry, A.G., Brooks, A.S. and Piperno, D.R. 2010. Microfossils in calculus demonstrate consumption of plants and cooked foods in Neanderthal diets (Shanidar III, Iraq; Spy I and II, Belgium) in PNAS: proceedings of the National Academy of Sciences of the United States of America, vol. 108, no. 2.

Henry, A.G. and Piperno, D.R. 2008. Using plant microfossils from dental calculus to recover human diet: a case study from Tell al-Raqā’i, Syria in Journal of Archaeological Science, vol. 35, issue 7. pp. 1943-1950.

Jenkins, E. L., Rosen, A. M. and Otsaku, M., 2012. The Phytoliths of the BACH Area. In: Tringham, R. and Stevanović, M., eds. Last House on the Hill: BACH Area Reports from Çatalhöyük, Turkey. Los Angeles, CA, USA: Cotsen Institute of Archaeology Press, 261 – 267.

Karkanas, P., Rigaud, J-P., Simek, J.F., Albert, R.M. and Weiner, S. 2002. Ash, bones and guano: a study of the minerals and phytoliths in the sediments of Grotte XVI, Dordogne, France in Journal of Archaeological Science, vol. 29. pp. 721-732.

Lancelotti, C. and Madella, M. 2012. The ‘invisible’ product: Developing markers for identifying dung in archaeological contexts in Journal of Archaeological Science, Vol. 39, Issue 4. pp. 953-963.

Malinsky-Buller, A., Hovers, E. and Marder, O. 2011. Making Time: ‘Living floors’, ‘palimpsests’ and site formation processes – A perspective from the open-air Lower Palaeolithic site of Revadim Quarry, Israel in Journal of Anthropological Archaeology, vol. 30. pp. 89-101.

Middleton, W.D. and Rovner, I. 1994. Extraction of Opal Phytoliths from Herbivore Dental Calculus in Journal of Archaeological Science, Vol. 21, Issue 4. pp. 469-473.

Piperno, D. R. 2006. Phytoliths: A Comprehensive Guide for Archaeologists and Paleoecologists, AltaMira Press.

Piperno, D.R. and Pearsall, D. 1993. The Nature and Status of Phytolith Analysis in Pearsall, D. and Piperno, D.R. (eds.). 1993. Current Research in Phytolith Analysis: Applications in Archaeology and Paleoecology, University of Pennsylvania Press.

Prasad, V., Stromberg, C.A.E., Alimohammadian, H. and Sahn. A. 2005. Dinosaur Coprolites and the Early Evolution of Grasses and Grazers in Science, vol. 310. pp. 1177-1180.

Saul, H., Madella, M., Fischer, A., Glykou, A., Hartz, S. and Craig, O. 2013. Phytoliths in Pottery Reveal the Use of Spice in European Prehistoric Cuisine in PLoS One, vol. 8, issue 8.

Guest Blog Post: Archaeobotany & Plant Use in Late Iron Age Silchester, Lisa Lodwick, University of Reading

Aerial view of the Late Iron Age archaeology in Insula IX Image © University of Reading Silchester Insula IX ‘Town Life’ Project

Aerial view of the Late Iron Age archaeology in Insula IX
Image © University of Reading Silchester Insula IX ‘Town Life’ Project

Archaeobotany has been a key part of archaeological science since the 1970s, and although the tried and tested techniques that form the basis of this study area (basically playing with buckets, water and sieves) have remained unchanged for decades, the research field continues to give new insights into the past as new sites and periods are studied. Archaeobotany (or palaeoethnbotany in America) usually refers to the study of plant macrofossils – seeds, fruits, leaves, twigs, nuts etc. Basically any plant remains which can be seen (just about) with the naked eye. Plant microfossils – starch and phytoliths, also come under the umbrella of archaeobotany, but I’m going to stick to the big bits here.

Plant macrofossils are all retrieved by either flotation – breaking up anywhere between 1-40L of sediment in a tank of water, and collecting the plant remains which float on the surface, or sieving – passing the sediment through a stack of sieves. The flot or sieve residues are then studied under a low power microscope, usually only up to x40 magnification. Archaeobotanists study plant remains preserved by four main types of preservation. These are very important to keep in mind, as they effect which seeds are preserved in the first place, how the seeds are separated from sediment, how hard it is to identify the seeds, and what type of information they are going to give us about past societies.

Charred Hordeum sp. (Barley) Grain  Image © Lisa Lodwick 2015

Charred Hordeum sp. (Barley) Grain
Image © Lisa Lodwick 2015

Second – mineralised plant remains. This is a pretty rare type of preservation. It normally occurs in cesspits, when calcium (from animal bones, marine shells, egg shells etc.) and phosphate (from human waste) enter into seeds/fruit stones, and form calcium-phosphate. This material will survive for millennia, but the range of casts and impressions formed (individual cell replacement, interior casts, exterior casts) can be tricky to identify. Nevertheless, mineralised plant remains provide us with fantastic evidence for diet and trade in plant foods, mainly for the Roman and Medieval periods.

Third – desiccated plant remains. In hyper-arid places (think Egypt) the bacteria which would usually decay plant remains cannot do so without any water. So, huge quantities of straw, cereal chaff, fruit stones and seeds survive in middens, mud bricks and in occupation deposits within buildings. Studies at trading settlements on the Red Sea have provided fascinating evidence for spices which were traded from India to the Mediterranean, and also more everyday activities like animal foddering and crop-processing (Van der Veen 2007).

Finally, waterlogged plant remains are in a way most similar to desiccated plant remains, but decay is stopped in this case by the lack of oxygen rather than water. Plant remains have to have been dumped into the standing water at the bottom of deep pits or wells, or discarded in towns with damp climates (like York!) where the rate of organic rubbish dumping was faster than decay. Waterlogged plant macrofossils are also preserved in off-site sequences, such as peat bogs and palaeo channels. The study of these usually falls under the realm of palaeoenvironmental studies.

The great thing about waterlogged plant remains is that they include plant foods which do not need to be exposed to fires during food preparation – like fruits, flavourings and vegetables. So, waterlogged samples typically produce a much more diverse range of plant foods than charred samples from the same site. Plus, waterlogged preservation is much more common than mineralisation in north-west Europe.

My research focuses on the development of “oppida” in the Late Iron Age and into the Roman period, and what the societies were like which inhabited these settlements. Whilst sampling for plant macrofossils has been widely undertaken for around 40 years, no oppida has been excavated during this period in a large enough scale, or with enough attention to systematic sampling (large well-recorded sediment samples from a wide range of deposits and site phases). So, we don’t know what foods the inhabitants were eating, and whether what crops they grew, and how they grew them, had to change as people decided to live in the first proto-urban settlements in Britain.

Luckily, the University of Reading Silchester Insula IX ‘Town Life’ Project has been excavating a large area of the oppidum Calleva Atrebatum over the last two decades. The reliance on wells for water supply to the settlement in the past, combined with the bulk sampling for plant remains throughout the excavation, meant a large dataset was available for study. Two Late Iron Age wells contained waterlogged plant remains. Whilst most of the sample consisted of seeds of weedy plants, which would have been growing around the mouth of the well, around 5% of the sample contents were seeds of cultivated plant foods. Several seeds of celery and coriander were present, alongside a few pieces of olive stone. These foods were previously thought to have been introduced to Britain by the Roman military after the Roman Invasion in AD 43, but we now know that some of the inhabitants of Late Iron Age Silchester were selectively adopting some of the plant foods being consumed elsewhere in the Roman world.

Mineralised Apium graveolens (Celery) seeds from a Roman cesspit at Silchester and Waterlogged Coriandrum sativum (Corainder) seed from an Early Roman well at Silchester; Excavation of the Late Iron Age Well at Silchester

Mineralised Apium graveolens (Celery) seeds from a Roman cesspit at Silchester
and Waterlogged Coriandrum sativum (Corainder) seed from an Early Roman well at Silchester; Excavation of the Late Iron Age Well at Silchester

The archaeobotanical dataset from Insula IX also includes substantial charred and mineralised datasets, showing  both continuation and change in farming and food consumption practices across centuries of occupation there. Whilst my research so far has focussed on the systematic application of long-standing archaeobotanical techniques, the development of new methods of statistical analysis, combined with exciting developments in the areas of crop stable isotope and aDNA analysis, means archaeobotany continues to provide new insights into the past.

A Late Iron Age well after excavation at Silchester  Image © University of Reading Silchester Insula IX ‘Town Life’ Project

A Late Iron Age well after excavation at Silchester
Image © University of Reading Silchester Insula IX ‘Town Life’ Project

References

Lodwick, L. (2014). Condiments before Claudius: new plant foods at the Late Iron Age oppidum at Silchester, UK. Vegetation History and Archaeobotany 23: 543–549.

Van der Veen, M. (2007). Formation processes of desiccated and carbonized plant remains – the identification of routine practice. Journal of Archaeological Science 34 (6), 968–990.

University of Sheffeld Integrated Archaeobotanical Research

About the Author

Lisa Lodwick is a Post Doctoral Researcher at the University of Reading, her current research focuses on analysis of plant macrofossils from Silchester. Lisa completed a BA in Archaeology and Anthropology and an MSt. in European Archaeology at the University of Oxford, before pursuing a PhD in Archaeology at the same institution. Lisa’s PhD research focussed on agricultural and social changes during the Late Iron Age to Roman transition period in Britain, identifying changes and continuities in consumption and production patterns. She occasionally blogs about her own research at https://theplantremains.wordpress.com/  and tweets much more frequently about archaeobotany @LisaLodwick . Lisa is also one of the team behind the successful Not Just Doormice – Food for Thought blog https://notjustdormice.wordpress.com/.

Guest Blog Post: Bone Diagenesis in the UK, Meriam Guellil, University of York

Although bone is seemingly never changing and durable, it is a tissue subject to constant change and prone to degradation throughout the life of an organism and beyond its death. These changes heavily affect the amount of information that remains available and visible to us and the way we should handle it. Especially in biomolecular archaeology, this is of crucial importance, since the degree of degradation usually dictates the suitability of the sampled material for analysis. Diagenesis represents the entirety of chemical, biological and physical processes occurring within a material or an organism during its conversion from the biosphere (sum of all ecosystems on earth) into the pedoshpere (outermost layer of earth), or in the case of archaeological samples its conversion from the biosphere to the state of preservation achieved by the time of excavation or analysis. Diagenesis as a process is generally understood in its separated components but as a whole phenomenon affecting the decomposing human body it remains a concept difficult to grasp in its entirety and variability.

There are a number of key criteria to consider when assessing the potential degree of degradation of human remains in an archaeological context: humidity, temperature, soil acidity, soil composition, biology of the individual at the time of death, postmortem body treatment and burial. Hydrology, temperature and soil composition will commonly be the deciding factor as to whether an environment is suitable for a good preservation and whether it will be aerobic (environment rich in oxygen) or anaerobic (environment poor or devoid of oxygen). This is important since most microorganisms involved in microbial degradation will be aerobic and therefore require an environment rich in oxygen to thrive, accordingly an anaerobic environment will generally have significantly less microbial activity, although a number of specialized anaerobic microorganisms will still be active. Each of the aforementioned criteria are often highly dependent on each other and have the potential for an immense impact on the final overall preservation achieved in the archaeological record within the conditions set by the combination of criteria present locally. This is true for the present and the past, since it cannot be assumed that the environmental conditions affecting an archaeological context have remained unchanged since its deposition (Guellil 2013; Hedges 2002; Nielsen-Marsh et al 2000). The exterior appearance of a bone or tooth has generally little to do with its overall preservation and can be very misleading. Instead of examining the exterior surface of a bone we have to take a good look at its microstructure. Typically, this is done by analysing the material histologically either via SEM or light microscope.

Different degrees of bone degradation as seen on two histological section from human bone samples, Coronation Street, South Shields, UK. Photos: © M.Guellil, University of Sheffield 2013.

Different degrees of bone degradation as seen on two histological section from human bone samples, Coronation Street, South Shields, UK.
Photos: © M.Guellil, University of Sheffield 2013.

Bone is mainly composed of hydroxyapatite and type-1-collagen, with the mineral portion making up 60-70% of its weight and the remaining 20% organic portion being composed of 90% type-1-collagen. The preservation of hydroxyapatite and collagen are closely tied together in the bone matrix and form a structural symbiosis. Collagen breakdown is subject to some debate but is generally considered to be caused by bacterial collagenase and hydroxyapatite breakdown is caused by inorganic weathering, e.g. soil acidity. However, the structure of bone is such that if one is broken the stability of the other will be in jeopardy (Currey 2006; Dent et al 2004; Gill-King 1997; Guellil 2013; Trueman and Martill 2002; Weiner 2010). The loosening of the bone matrix caused by collagen leaching usually leads to a facilitated access to the bone for microorganism, who in turn will increase the porosity of the bone by tunneling through the already damaged and weakened matrix. Generally speaking these agents are divided into microbial and fungal degradation and leave very distinctive marks on the bone microstructure called microscopical focal destruction or MFD. After skeletonization the survival of bones is mostly dependant on inorganic weathering and mechanical stress. Ideally speaking a good preservation of skeletal remains is guaranteed in a neutral or slightly alkaline anaerobic cold environment (Dent et al. 2004; Jans et al. 2004, 87; Weiner 2010, 113-114).

Two histological sections from human bone samples, Coronation Street, South Shields, UK. The section on the right has been photographed under polarized light. You can clearly see the collagen fibrils, showing up as birefringence on the slide and the corresponding darker, already damaged sections of bone.   Images © M.Guellil, University of Sheffield 2013.

Two histological sections from human bone samples, Coronation Street, South Shields, UK. The section on the right has been photographed under polarized light. You can clearly see the collagen fibrils, showing up as birefringence on the slide and the corresponding darker, already damaged sections of bone.
Images © M.Guellil, University of Sheffield 2013.

The degree of degradation affecting bone is generally considered to be set at a very early stage of its deposition and seems to be subject to very little change after ca. 500 years and literature has been debating about the origin and characterisation of the agents affecting bone degradation. To predict anything when so many factors are prone to variability is a challenge that can only be addressed by collecting more data and gaining an understanding for the small links that hold the bigger picture together (Guellil 2013; Hedges 2002; Hollund et al. 2012; Trueman and Martill 2002). With new technology and screening techniques emerging, which are able to deal with sample degradation up to a certain level, we can now extract viable data from degraded materials, from which we would not have been able to sample in the past. However, the final yield itself and its quality will always depend on the degree of degradation and the depositional environment the sample source was subjected to.

About the Author:

Meriam Guellil is a Research Associate in the Biology Department at the University of York, working within the BioArCh Research Cluster. Her research focuses on Ancient DNA, BioInformatics and Taphonomy, working on a range of samples from Canada, Italy and the UK. Meriam completed a BA in Prehistoric Archaeology and Early History at the University of Vienna, Austria, followed by an MSc in Human Osteology and Funerary Archaeology at the University of Sheffield.

Select References:

Dent, B.B., Forbes, S.L. & Stuart, B.H., 2004. Review of human decomposition processes in soil. Environmental Geology, 45(4), pp.576–585.

Currey, J.D., 2006. Bones: Structure and Mechanics, Princeton University Press.

Gill-King, H., 1997. Chemical and ultrastructural aspects of Decomposition. In Forensic taphonomy: the postmortem fate of human remains. CRC, Boca Raton, FL. pp. 93–108.

Guellil, M., 2013. Determining the Intensity of Microbial Degradation in Selected Skeletal Elements. Unpublished Dissertation, University of Sheffield.

Jans, M.M.E. et al., 2004. Characterisation of microbial attack on archaeological bone. Journal of Archaeological Science, 31(1), pp.87–95.

Hedges, R.E.M., 2002. Bone diagenesis: an overview of processes. Archaeometry, 44(3), pp.319–328.

Hollund, H.I. et al., 2012. What Happened Here? Bone Histology as a Tool in Decoding the Postmortem Histories of Archaeological Bone from Castricum, The Netherlands. International Journal of Osteoarchaeology, 22(5), pp.537–548.

Nielsen-marsh, C. et al., 2000. The Chemical Degradation of Bone. In Human Osteology: In Archaeology and Forensic Science. pp. 439–454.

Trueman, C.N. & Martill, D.M., 2002. The long–term survival of bone: the role of bioerosion. Archaeometry, 44(3), pp.371–382.

Weiner, S., 2010. Microarchaeology: Beyond the Visible Archaeological Record, Cambridge University Press.

Guest Blog Post: Red Sea shellmounds of Saudi Arabia, Niklas Hausmann, University of York

Farasan Islands
Fieldwork in the Farasan Islands © N. Hausmann 2014

The west-coast of Saudi Arabia is a desert landscape with temperatures ranging between 22°C  and 38°C. There are no rivers or lakes and the maximum rainfall one can expect per month is only 22 mm. Data from environmental proxies indicate that these conditions have been the same for the last 7,000 years (Lézine 2014).

However, this did not keep people from living there. Vast amounts of coastal sites were found all over the southern coast of the Red Sea (Meredith-Williams et al. 2014). Most of the known sites are located on an archipelago called the Farasan Islands (www.disperse-project.org). Excavations and surveys in 2006-2009 found over 3,000 sites on the big islands alone (Bailey et al. 2007). The main part of the sites is  made up of shell middens, this type of site can be found all over the world (Colonese et al. 2011, Estévez et al. 2001, Gutiérrez-Zugasti et al. 2011, Rabett et al. 2011), examples in the UK include shell mounds on the Isle of Portland (Mannino and Thomas 2001).

Shell middens are the leftovers from people collecting and processing molluscs and then depositing the remains on the beach. But many middens do not only contain shells. They also contain other food remains, burials, lithic tools, housing structures, etc.

Picture of basket remains in section of shell midden Cubatão, Brazil, 3,000 cal. B.P.  © N. Hausmann 2014

Picture of basket remains in section of shell midden Cubatão, Brazil, 3,000 cal. B.P.
© N. Hausmann 2014

It is the rigid structure of the shell as well as its chemical composition that works like a shelter for artefacts and bones. This also means that sometimes the only finds that are preserved can be found inside the middens, making them a prime location to look for intact material which later can be used for scientific analyses (e.g. residue analysis (Heron et al. 2007)).

The shells themselves can be used to ask questions about food preference and subsistence strategies. How many oysters did people eat? Did they prefer to eat fish or other mollusc species (Álvarez-Fernández 2001)? But also, was the local marine environment possibly unsuitable for some species? Can we see a change in marine environment that is reflected in a change of species throughout time (Carbotte et al. 2004)? These are all questions that can be looked into by analysing the animal remains and the taxonomic data.

For Farasan we try to answer other questions as well. For example we analyse the elemental and isotopic composition of the shell growth rings to reconstruct the temperature that the shells lived in. For this δ18O values from the shell carbonate (δ18OS) can be used in combination with the water composition (δ18OW) to calculate an estimated temperature using the equation below (Dettman et al. 1999).

SST (ºC) = 20.6 – 4.34 (δ18OS – (δ18OW – 0.27))

This can help us to understand what the temperatures were like in the past but also how dry or humid it was. This is especially interesting in desert landscapes like Saudi Arabia.

Furthermore, by sampling multiple growth rings in a line the temperature reconstruction can be used to find out about the seasonal change throughout the year. Goodwin et al. (2003) described the change in the seasonal curve for different scenarios.

Simplified δ18O profiles (Goodwin et al. 2003)

Simplified δ18O profiles (Goodwin et al. 2003).

However, the isotopic change is different for every shell species and different in every environment. The scenarios only illustrate what characteristics can be found in data.

The seasonal isotopic change in the shell carbonate can also indicate at what time of the year the mollusc was killed and when the people who made the shell midden ate it. Eerkens et al. (2013) used this technique to track people’s movement within the San Francisco Bay area. On Farasan we will be able to look if people moved to and from the islands at specific times of the year and if there has been a strong connection to the Arabian mainland. We could find that people stayed on the islands for the whole year to enjoy the rich marine wildlife.

Marine Resources: Fish in a Basket. © C. Beresford 2014

Marine Resources: Fish in a Basket.
© C. Beresford 2014

Fishing in the Red Sea. © C. Beresford 2014

Fishing in the Red Sea.
© C. Beresford 2014

About the Author:

Niklas Hausmann is a PhD Researcher within the Department of Archaeology at the University of York. His research is part of the DISPERSE Project, working on the Farasan Islands in the southern Red Sea. His research examines the isotopic composition of shells on the Farasan Islands, which feature more than 3000 shell middens, using the isotopic signature as an environmental proxy for sea surface temperatures (SST). Niklas hopes that the resulting understanding of seasonality can reveal subsistence strategies of local prehistoric populations, revealing gathering strategies and shellmound construction methods. Abundant shells within each layer of the middens provide a high density of samples, providing a high resolution dataset reflecting pre-desertification coastal exploitation in Saudi Arabia. Niklas undertook a BSc in Prehistoric and Historic Archaeology with Geosciences at Christian-Albrechts-Universität (CAU) Kiel, Germany, his dissertation focussed on the analysis of Kongemosian and Ertebølle lithic technology and faunal assemblages from Satrup LA 2. He then completed an MA in Mesolithic Studies at the University of York, focussing on spatial analysis of lithics from Duvensee 13. He is due to complete his PhD in September 2015.

References:

Álvarez-Fernández, E. (2011). “Humans and marine resource interaction reappraised: archaeofauna remains during the Late Pleistocene and Holocene in Cantabrian Spain”. Journal of Anthropological Archaeology, 30(3), 327-343.

Bailey, Geoff N., Nic C. Flemming, Geoffrey CP King, Kurt Lambeck, Garry Momber, Lawrence J. Moran, Abdullah Al-Sharekh, and Claudio Vita-Finzi 2007. “Coastlines, submerged landscapes, and human evolution: the Red Sea Basin and the Farasan Islands.” The Journal of Island and Coastal Archaeology 2, no. 2 : 127-160.

Carbotte, S. M., Bell, R. E., Ryan, W. B. F., McHugh, C., Slagle, A., Nitsche, F., & Rubenstone, J. 2004. “Environmental change and oyster colonization within the Hudson River estuary linked to Holocene climate”. Geo-Marine Letters, 24(4), 212-224.

Colonese, A. C., Marcello A. Mannino, D. E. Bar-Yosef Mayer, D. A. Fa, J. C. Finlayson, D. Lubell, and M. C. Stiner 2011. “Marine mollusc exploitation in Mediterranean prehistory: an overview.” Quaternary International 239, no. 1: 86-103.

Dettman, D.L., Reische, A.K., Lohmann, K.C. 1999. Controls on the stable isotope composition of seasonal growth bands in aragonitic fresh-water bivalves (Unionidae). Geochimica Et Cosmochimica Acta 63 (7–8), 1049–1057.

Eerkens, J. W., Byrd, B. F., Spero, H. J., & Fritschi, A. K. 2013. “Stable isotope reconstructions of shellfish harvesting seasonality in an estuarine environment: implications for Late Holocene San Francisco Bay settlement patterns”. Journal of Archaeological Science, 40(4), 2014-2024.

Estévez, J., Piana, E., Schiavini, A., & Juan‐Muns, N. 2001. “Archaeological analysis of shell middens in the Beagle Channel, Tierra del Fuego Island”. International Journal of Osteoarchaeology, 11(1‐2), 24-33.

Goodwin, D. H., Schöne, B. R., & Dettman, D. L. 2003. Resolution and fidelity of oxygen isotopes as paleotemperature proxies in bivalve mollusk shells: models and observations. Palaios, 18(2), 110-125.

Gutiérrez-Zugasti, Igor, Søren H. Andersen, Ana C. Araújo, Catherine Dupont, Nicky Milner, and Antonio M. Monge-Soares 2011. “Shell midden research in Atlantic Europe: state of the art, research problems and perspectives for the future.” Quaternary International 239, no. 1: 70-85.

Heron, C., Craig, O. E., Forster, M., Stern, B., & Andersen, S. H. 2007. “Residue analysis of ceramics from prehistoric shell middens in Denmark: Initial investigations at Norsminde and Bjørnsholm”. Shell Middens in, Atlantic Europe, 78-85.

Mannino, Marcello A., and Kenneth D. Thomas 2001. “Intensive Mesolithic exploitation of coastal resources? Evidence from a shell deposit on the Isle of Portland (Southern England) for the impact of human foraging on populations of intertidal rocky shore molluscs.” Journal of Archaeological Science 28, no. 10: 1101-1114.

Meredith-Williams, M.G., Hausmann, N., Inglis, R. and Bailey, G. 2014. “4200 New Shell Mound Sites in the Southern Red Sea”. ‘Human Exploitation of Aquatic Landscapes’ special issue (ed. Ricardo Fernandes and John Meadows), Internet Archaeology. http://dx.doi.org/10.11141/ia.37.2

Lézine, Anne-Marie, Franck Bassinot, and Jean-Yves Peterschmitt 2014. “Orbitally-induced changes of the Atlantic and Indian monsoons over the past 20,000 years: New insights based on the comparison of continental and marine records.” Bulletin de la Societe Geologique de France 185, no. 1: 3-12.

Rabett, Ryan, Joanna Appleby, Alison Blyth, Lucy Farr, Athanasia Gallou, Thomas Griffiths, Jason Hawkes 2011. “Inland shell midden site-formation: Investigation into a late Pleistocene to early Holocene midden from Tràng An, Northern Vietnam.” Quaternary International 239, no. 1: 153-169.

Sangarungu

Songo Mnara is not as easily accessible as Kilwa Kisiwani; travelling by boat from the port at Kilwa Masoko we approached a picturesque fishing village at Sangarungu, palm frond makuti structures emerging from a clearing within the mangroves and palms on white sands. Sangarungu is a working fishing village and despite the seemingly remote location by British standards, there’s a small shop for the fishermen selling Fanta Passion and other supplies, ice is shipped from the mainland to preserve the recently gutted fish on wooden platforms just off the beach.

The journey to Songo Mnara

This route is only accessible in low tide as the boat moors just offshore, so you have to wade to the beach. Passing through Sangarungu, white sand stuck to our wet feet as we walked through palm plantations and mangroves, curious monkeys crashed through the trees, just out of sight. The sandy path sloped downwards into the Mangrove swamp, the barrier between the sandy island of Sangarungu and Songo Mnara; at low tide we walked down into a cutting, into the dense shade of the mangroves, twisted roots emerging from the sand.

We waded through the shallows for 150m to Songo Mnara, to the sound of water being pushed violently ahead by our legs, solitary mangrove fruits floated past poised to anchor into the sand and fill in the gap left by the cutting. The brave and adventurous might try to keep their shoes on and their feet dry at low tide, by traversing the mangrove roots at the edge of the path. At higher tide, we waded into chest deep clear water, despite the organic blackness of the mangrove sediments; carrying our bags on our heads to keep them dry as small shoals of fishes swam past. Emerging on white sands we reached Songo Mnara, on the very edge of the intertidal zone.

Harbour Songo Mnara

At high tide, when the tide is too high to wade through the mangroves from Sangarungu, we instead approached a shallow cove of clear blue water to the north of Songo Mnara. Coral rocks cropped up through the water hiding small shoals of small black and white tropical fish, mangroves, visible at low tide, peering through the waves, protecting the natural inlet; we scrambled from the side of the boat up the coral bluffs, entering through a thicket, emerging onto white sands studded with tall Coconut palms.

The ruins of Songo Mnara lie on the edge of a large Coconut palm plantation, pale grey ruins surrounded by lush green vegetation. At first, you can barely make out the crumbling coral walls peering through trees and lianas, but then you begin to see the walls emerge, picking out buildings, seeing the city develop before your eyes. Every now and then, a loud crack punctuates the silence, as a Coconut palm branch falls. Whilst the abandoned buildings decayed, huge Baobab trees sprung up next to the ruins, growing stronger, almost eclipsing the monumentality of the buildings; introduced by the inhabitants of the buildings, their presence is a natural reminder that this was once a busy urban trade town.

Baobabs and Buildings

Songo Mnara Palm Plantation

From the Site Diary: Approaching Songo Mnara

Day of Archaeology 2014 – Counting Phytoliths from Songo Mnara, Tanzania

This is my first blog post, for Day of Archaeology 2014!! Right now, I spend my life counting phytoliths – over 3500 phytoliths so far….What’s a phytolith and why does it get me out of bed and into the lab before 7am? How did you not realise this was such an exciting archaeological technique? Phytoliths are a bit like plant negatives; essentially the plant absorbs monosilicic acid (H4O4Si) from its water supply and during transpiration as the water ‘leaves’ the plant, the monosilicic acid becomes solid opaline silica. It has to go somewhere, so it fills in gaps within the cell structure of the plant. These gaps are either within the cells, or surrounding the cells, making silica negatives of the internal cell structure. Not all plants make phytoliths though, just like not all plants preserve well as charred plant macrofossils, and not all pollen grains enter the local archaeological record or preserve well. Plants have to degrade in situ for the phytoliths to be included in the archaeological record, no technique is perfect. But the key is, that phytoliths are well preserved in a variety of contexts and can add to our understanding of plant use; not only on sites with poor preservation of plant macrofossils and pollen, but also in contexts where plant remains may not have entered the archaeological record following charring. For example, organic crafts such as grass or palm matting may not be preserved by charring and therefore might be invisible on archaeological sites without waterlogged preservation. These may be visible through phytolith analysis if they have degraded in situ. To help identify diagnostic phytoliths I collected lots of plant samples from the field and I’m now creating a phytolith reference collection in the lab. It’s not a magic bullet to help us understand plant use in the past, but it is pretty cool! I’m working on late 14th to early 16th Century samples from Songo Mnara, a Swahili stonetown in Tanzania, part of the Songo Mnara Urban Landscape Project [1]. Songo Mnara is part of the Kilwa Archipelago and it’s linked to other settlements and islands along the East African coast through the Indian Ocean Trade network. Songo Mnara has truly amazing preservation of stone buildings!! To get to the site you have to take a Dhow from Kilwa Masoko with a guide and once you arrive on the island you have to wade through a tidal Mangrove swamp which can be anything between ankle deep and chest high! It’s off the beaten track, for sure.

Blog 1. Songo Mnara Buildings

© Hayley McParland-Clarke 2013

During the 2013 excavation season, two types of structure were excavated; a stone house divided into rooms and a collapsed wattle and daub structure, which appeared open plan. Initially it was thought that the monumental stone architecture in the town was standing in an open area, but extensive test pitting by Dr Fleisher combined with Geophysical and Magnetometer survey[2] revealed the presence of concentrations of daub within this space. Excavation exposed two wattle and daub structures with comparable finds assemblages to that of the stone structures. The phytoliths I’m looking at today come from Trench 32, one of the daub structures. Spot samples were taken across the entire packed sand floor surface of the structure on a 1m grid, in order to assess whether phytolith analysis can be used as a tool for spatial analysis and to understand the use of plant materials within the structure. Samples were also taken from the ‘outside’ of the structure in the open area to identify clear differences in the phytolith assemblage between ‘inside’ and ‘outside’ and to see if it was possible to recreate the environment immediately adjacent to and further away from the structure.

Sampling for Phytoliths at Songo Mnara © Hayley McParland-Clarke 2014

Sampling for Phytoliths at Songo Mnara © Hayley McParland-Clarke 2014

I’m really hoping that we’ll be able to see activity areas within the structure through the plant assemblage, for example food preparation areas or areas of matting. It may be possible to identify construction materials such as wood, or roofing materials such as palm thatch. I’m also hoping to see evidence of Indian Ocean Trade through phytoliths from imported edible plants within the assemblage, but as with all archaeology I can hope for lots of things, it doesn’t mean it’s there! We also sampled the stone house, which is really interesting, because it has clear rooms within it, whereas those divisions weren’t clear when excavating the daub structure. Phytolith analysis might enable us to see the limits of the daub structure by providing an ‘inside’ and an ‘outside’ botanical signature. The process of counting involves using a high powered microscope at x400 magnification to identify phytoliths, photograph them, measure them and count them. I count around at least 250 per slide, which means that I’ve counted thousands from this site so far, and I’ve a lot more to do! Phytoliths are 3D objects, but when you’re looking down the microscope you only see the 2D image, which means that you have to remember that each phytolith type might look different depending on which angle you’re looking at it from! Phytoliths aren’t always round like pollen, in fact they’re frequently not round at all, they come in all shapes and various sizes! Although lab work is often thought of as completely different to fieldwork, it’s sort of the same. I search through transects on the slide, much like layers of stratigraphy looking for microscopic evidence in the form of phytoliths rather than artefacts. It can take a long time, it’s systematic and sometimes I don’t find anything of interest. Recording stratigraphy on site tells you a lot about site formation processes and human actions, likewise recording information about the slide assemblage is useful. For instance, lots of phytoliths which are still articulated suggests that there was little bioturbation, or lots of microcharcoal might suggest burning episodes.

Microscope

© Hayley McParland-Clarke 2013

I’m on my last few slides from this pilot study now, and I’ve started to get an idea of what’s happening in the structure which is really exciting. Each phytolith assemblage has a different character, which suggests that the spatial approach might be working!! I can clearly see a difference between the assemblages from the floor surface ‘inside’ the building and the outside; I can also see variations across the floor surface within the structure. Future research will focus on the comparison of the stone house and the daub structure to see if there’s a difference between the uses of each structure. I also hope to look at some of the open area samples to try to understand how the urban landscape impacted on the local environment. Follow my progress and find out more about phytolith analysis, archaeobotany and archaeology by checking in here every now and then, or follow me on twitter @hayley_mcp.   [1] Managed by Dr Stephanie Wynne-Jones and Dr Jeff Fleisher, funded by the NSF and AHRC. [2] Welham, K., J. Fleisher, P. Cheetham, H. Manley, C. Steele, and S. Wynne-Jones. 2014. Geophysical Survey in Sub-Saharan Africa: Magnetic and Electromagnetic Investigation of the UNESCO World Heritage Site of Songo Mnara, Tanzania. Archaeological Prospection.