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Reducing the risk of windthrow to archaeological evidence in woodland

henv_windthrow.jpgDamage to archaeological evidence

When a tree is thrown and the root-plate heaved up, it will inevitably lift soil with it. This will elevate or expose any near-surface archaeological material, may cause physical damage and remove the evidence from its correct context. Many factors influence the susceptibility of trees to windthrow (such as location, soil type, species and woodland management) and considerable research has been undertaken to understand the relationships between them. Upland conifer plantations are often sited on thin or waterlogged soils producing trees with shallow root systems. If tree felling occurs around archaeological sites in these plantations, this can increase the exposure and risk of windthrow to the remaining trees. Thus, forest felling plans must take this risk into account.

Windthrow predictions

Modern technology has allowed the evolution of windthrow prediction. Early methods for scoring windthrow susceptibility considered the region of the country (wind zone) in which the site occurs, the elevation, exposure, soil type and aspect. These were then related to the tree height and stocking density, factors which are especially important for upland forests at higher risk from windthrow. A more recent computer based model (ForestGALES) uses additional information on the crop and silvicultural regime.

Management options

In upland areas where the risks from windthrow are greatest, windthrow predictions should be made before deciding to open up an archaeological site, improve access or enhance the landscape setting. If a few trees exist on a burial mound and are at risk of windthrow, then pruning the tree and removing some of the above ground biomass may be an alternative to felling. This will reduce the risk of windthrow whilst maintaining the structural integrity of the slope. Such advantages are seen in coppice silviculture.

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