What do tree rings tell us?

What do tree rings tell us?

What do tree rings tell us?

Tree rings are full of valuable information. They are especially informative about past climatic events and have great value when combined with other techniques in understanding climate change. Several climatic factors influence wood ring width and composition, particularly rainfall, temperature and carbon dioxide concentration.

We see changes in the past few centuries that indicate rising post-Industrial Revolution CO2 concentrations (‘heavy’ carbon isotopes), the great droughts of the past century and the cool periods that we call mini-Ice Ages, such as 1600-1900.

Other techniques that can be used to identify past climates rely upon stable isotopes (e.g. 18oxygen), pollen, charcoal and fossilised organisms such as phytoplankton and diatoms. ‘Heavy oxygen’ is extracted from ice cores to determine past temperature regimes while other proxies for past climates are variously found in ocean sediments (e.g. Baltic Sea), lake beds (e.g. Lake George near Canberra) and peat beds (e.g. Lynch’s Crater in Queensland). Coral reefs are also priceless records of past climatic events, with floods and temperature fluctuations recorded in the chemistry and banding of the corals. Even lichens and cactus spines can be used together with wood rings to infer past climates.

The timber of each tree species has its own distinctive pattern, rather like finger printing, allowing accurate identification of the tree from which the timber was cut. All trees from a known location have a similar pattern of growth rings but because of variations in climate; trees from other locations will have quite different patterns. Thus dendrochronology can provide a valuable tool for archaeologists and historians. The technique has been used to determine the place of origin of ships, timber in houses and many other wooden items, such as panels for paintings. Differences in tree ring and ray cell patterning can be used to identify the place of origin of timber, such as in Egyptian sarcophagi. Many 15th and 16th century paintings from the Netherlands were painted on panels of Baltic Oak (Quercus petraea) shipped from the Vistula River in Poland.

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