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The silvicultural practice used to establish woodland or forest cover will vary with the site conditions. Before any woodland cover can be established, some cultivation may be required to promote optimum root growth. Drainage, topography, fertility, previous land use and soil type all influence the choice of tree species and any necessary site preparation.
Whether through forestry or agriculture, ploughing is frequently attributed to the loss of archaeological evidence. In forestry, ploughing has been most widespread in the uplands, particularly on wetter sites. On drier soils or where restocking is occurring, the use of scarifiers or mounders is often preferred. Deep ploughing is rare today and actively discouraged by the Forestry Commission. With the increased ability of woodland managers to diversify and select trees for nature conservation, site aesthetics, community woodlands or other non-commercial benefits, species may now be selected that better suit a site, requiring little or no cultivation.
Any process involving substantial ground disturbance will potentially damage any archaeological remains buried near the surface. Thus, no area identified for archaeological conservation should be ploughed, ripped or scarified. On some larger sites such as field systems or cairnfields that may cover several hectares, some degree of tree cover may be acceptable. Here, any cultivation requirements should be discussed with a local authority archaeologist to develop a suitable mitigation strategy for the site.
Most British trees are unable to grow in soils that are permanently waterlogged and drainage may be necessary, especially in the uplands where poorly drained gleys and peaty soils are common. Drainage will have a greater effect on soil water content than tree growth. Information on the depth and extent of archaeological evidence and water table properties would significantly aid mitigation strategies, but such detail is often unknown. River valleys and floodplains have provided desirable settlement locations since prehistory and many may have a high archaeological potential containing well-preserved remains in waterlogged deposits. Any expansion of floodplain forestry or wet woodlands may therefore have implications for the buried archaeological resource.
Tree planting can be mechanised, but is predominantly a manual task and involving relatively minor soil disturbance. Direct sowing of seed is less common and most young trees are derived from nursery-grown stock where they have been subjected to undercutting or transplanting. Both these processes remove any taproots and stimulate more lateral growth. Significant physical damage to archaeological sites through the direct action of tree planting is unlikely to occur, as the ground disturbance is minimal.
Any chemical effects on buried remains due to the application of either herbicide or fertiliser is difficult to summarise as their chemical compositions vary considerably.
Of the mineral fertilisers, rock phosphate (Apatite) is the most common. This is very similar in chemical composition to bone and teeth and its application may even be beneficial in the preservation of such remains. Potassium salts (chloride or sulphate) are both highly soluble and are unlikely to exist for a long period in a well-drained soil. Nitrogen is applied in the form of ammonium nitrate or urea, and such compounds are known to acidify soil. Urea is the more commonly used, but no fertilisers are applied in large amounts in forestry. Nitrogenous compounds are also readily broken down in the soil. Occasionally, fertilizers can be applied in the form of organic wastes, such as sewage derived products. These are fairly neutral in pH and are unlikely to have a significant impact on any buried evidence.
Herbicide application to remove competing weeds is common during establishment as manual weeding is relatively expensive and mechanical methods are often ineffective. Herbicides vary in composition and more species selective products are constantly being developed. They are usually organic based molecules that interrupt enzyme function and block metabolic pathways. Some such as “Glyphosate” are contact herbicides that are inactivated by soil contact and quickly broken down. Others applied in pellet form to the soil have a longer lifespan. Some of these compounds are acidic and may be corrosive to certain types of archaeological evidence, but are applied at low concentrations per unit area.
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