Wood

Wood is a solid, fibrous tissue of cellular structure obtained from trees and shrubs, a natural composite of cellulose fibers in a lignin matrix. It has been used since early prehistory as a fuel and as a material for constructing structures and artifacts. Although ubiquitous in the past, wood rarely survives in the archaeological record. Some have argued that part—or all of—the Stone Age should be called the Wood Age, as stone tools are an aid to cutting and working wood. Aimé Michel and Michel Noël argued that the Neolithic was the Wood Age based on the number of wooden artifacts from this period that have been recovered from bogs and lakes and their level of technical sophistication. Wood use declined but is now increasing again in the early 21st century because of environmental concerns. However, 21st-century usage must take into account issues such as ecosystem awareness and sustainability.

Burial in moist aerated soils will usually lead to complete nonsurvival of wood. Acidic or highly alkaline deposition environments break up the cellulose content, leaving wood soft and caseous. Typically, archaeological wood survives sealed in a waterlogged environment where anoxic conditions inhibit microbial activity. Waterlogged wood is inevitably weakened to some degree and must be kept wet as loss of water content will lead to irreversible damage as surface tension effects in the water pull the wood's structure apart. Deep burial [Page 1004]below the level at which bacteria are active can also preserve wood, such as the remains of three medieval bridges buried under river-deposited sand and gravel and excavated from Hemington Quarry, Leicestershire.

Some of the largest wooden structures recovered from the archaeological record are shipwrecks and the remains of docks and bridges. These are preserved initially by waterlogging but often become buried by sediments, such as the Hemington bridges. Many factors are involved in determining the preservation level.

The Mary Rose, for example, a 16th-century warship that sank in the Solent, was partially preserved by sinking broadside onto the current, which then deposited silts inside the ship and scoured a pit into which part of the wreck fell and was sealed by a shelly seabed that formed over the wreck in the late 17th century. Another factor conferring preservation was the speed and angle of sinking, which embedded the ship deep into the seabed clays.