Compared to the chemistry of the burial environment, little has been published on soil fauna and their impacts on the archaeological resource. However, understanding of such activity is highly relevant to preservation.
Grassland often contains a rich microbial and earthworm community and the latter may in turn support larger fauna such as moles. The soil biota under different tree species will vary and may be either a greater or smaller number than that found under pasture. The soil type and properties will be highly influential in determining their population.
Woodland litter and soil fauna
Converting land to woodland will usually result in an increased litter deposition. The nature of this litter will depend upon the existing soil type, the soil organisms present and the species of tree planted. However, one common feature will be increased moisture in the upper soil horizons due to the high water retaining capacity of organic matter. Scrub and woodland development leads to an increased carbon input from leaves and woody material. Both arecomprised of more complex structures such as lignin and polyphenols that are less palatable to many soil fauna resulting in accumulation within the soil.
Complex but close relationships exist between the type of litter (dependant on tree species) and the form of humus produced. Humus is formed by the incorporation of organic matter (mull) or its accumulation on the surface (mor) and different groups of soil organisms are associated with each type.
- Mull is the less acidic and supports a larger faunal population, resulting in rapid breakdown and incorporation into the mineral horizons. Mull is usually associated with broadleaf woodlands.
- Mor is less palatable to soil fauna and supports a smaller range of species. It is therefore not readily broken down and incorporated into the mineral soil and accumulates on the surface. Mor is typical of most conifer woodlands.
Examples of faunal impacts on archaeological evidence
Earthworms can have a big impact on archaeological remains, as they can move significant quantities of soil resulting in the gradual burial through the "worm sorted layer". Worm activity on archaeological sites is recognised as causing a potential loss of archaeological context through artefact movement. Most earthworms avoid soils of low pH and litter with high lignin content, and may be absent from some types of woodland.
To a lesser extent, ants alsomove fine soil above the existing ground surface, which may incorporate small objects. Their activities have been proposed as the mechanism for the uniform fill often found in post-holes. Ants generally build their nests in areas that receive good sunlight and thus are more common in open areas of grassland or under broken canopy.
More specific studies into the impacts of different soil fauna on archaeological evidenceare needed.