The Compilation of a British Lowland Heathland and Agricultural Grassland Phytolith Reference Database and its application at the archaeological site of Wytch Farm, Poole Harbour, Dorset

Osborne, Sigrid (2023) The Compilation of a British Lowland Heathland and Agricultural Grassland Phytolith Reference Database and its application at the archaeological site of Wytch Farm, Poole Harbour, Dorset.

The aim of this project was to compile the photographic phytolith reference data base for comparative purposes and then apply the data base as an analytical tool on a Late Anglo-Saxon archaeological site located within a lowland heathland setting on the Southwest coast of Britain. Three British Isle habitats, agricultural grassland, lowland heathland, and an experimental agricultural field, were used for the reference collection. Plants collected from these habitats in late autumn led to the compilation of a website that shows the plant’s phytoliths (httms://phynd.online). The website and phytolith soil analysis conducted at Wytch Farm were then combined to interpret a 1000-year-old soil build up overlying a late Anglo-Saxon saltern site. Other environmental proxies were integrated such as: pollen analysis, geochemical analyses using portable x-ray florescence (pXRF), magnetic susceptibility to examine burning levels, soil pH and loss on ignition to examine the soil’s organic content. The combined analysis has led to methodological observations on the extraction of phytoliths from British native plants and an interpretation of the Wytch Farm soil build up and anthropogenic use of the site. An experiment was included to establish the link between plants growing above ground and phytoliths detected in the soil A horizon. This did not prove successful, and the results did not improve when pollen data was added. Most of the archaeological soil samples analysed contained single phytoliths in large numbers. However, the analysis suggested that identification to plant species through phytoliths is difficult because of a lack of multicelled phytoliths observed. The dry ashing process of the modern plants used for the reference data base showed that plants did produce multicells. The pXRF results showed that silica is present in the Wytch Farm soil, and therefore multicells should be present. A possible answer might be that weak bonds are formed within the multicells due to low transpiration rates within a temperate climate zone. This means that post depositional taphonomic conditions account for the lack of multicelled forms preserved in the archaeological samples. At the Wytch Farm site the application of single phytolith counts over time and through different contexts (core samples and micromorphology subsamples) together with the other proxies pointed to a site that since late Anglo-Saxon times has been used for agricultural and industry related activities (salt production and metal working) and did not revert back to a lower heathland landscape over that 1000-year time period. Agricultural practices that could be inferred were grazing, cereal production and possible burning of stubble fields. There was clear indication for a water edge clearing event right at the start of the saltern production site and the presence of repeated flooding events for the lowest soil strata. A rise in burnt phytoliths in certain areas together with the magnetic susceptibility results seems to indicate areas with high temperature burning processes.