DENDROCHRONOLGY

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DENDROCHRONOLGY
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General Principles

• In most trees, new water and food-conducting
  cells are added to the outer perimeter of the
  trunk at the start of each growing season
  following an inactive period in winter.

• Early in the growth season there is more demand
  for water so the cells tend to be larger in
  spring than late summer.

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General Principles

• As the cells get smaller, their walls get larger
  and form a distinct line between annual growth of
  wood.

• These lines (tree rings) allow the age of the
  tree to be established.

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General Principles

• Tree-ring width is seldom uniform. It is
  affected by a range of environmental factors and
  there are variations between species.

• The most important factor for tree ring growth
  is climate. The more favourable the conditions,
  the better the growth rate and the wider the tree
  rings.

• Determining climatic variations using tree ring
  growth is called dendroclimatology.

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Dendrochronological Procedures - Measurement

• Dead trees can be cut so that a complete cross
  section can be examined.

• Living trees can be sampled using a metal corer
  that extracts small diameter cylinders of wood
  from the tree trunk.

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Crossdating

• This is the technique of matching rings within
  trees from certain geographical areas.

• Distinctive rings, or groups of rings form
  markers which can be used to match trees with
  overlapping age ranges.

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Standardisation

• Trees grow faster when they are younger so there
  is usually a reduction in ring width with age.

• Each tree ring series is therefore standardised
  by changing the measured ring width values to
  ring width indices.

• This makes it hard to distinguish whether change
  is due to age or environment.

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Complacent Rings

• A complacent tree ring series is one which shows
  little variation.

• They are not very useful for crossdating because
  there are no distinctive markers.

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Sensitive Rings

• A sensitive series of rings shows a clear
  response to stress.

• Stress depends upon factors such as the slope of
  the ground surface, water-retentive capacity of
  the soil and the relative amount of shade and
  exposure.

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Missing Rings

• Trees are deliberately selected from stressed
  situations.

• There is always the possibility that during
  years of extreme climatic conditions a tree may
  fail to manufacture new cells.

• This is referred to as a missing ring.

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Bristlecone Pine

• Some of the oldest trees in the world grow in
  the American southwest mountains.

• The bristlecone pine can live in excess of 4000
  years. They are characteristically twisted and
  found in dry, rocky sites.

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Bristlecone Pine

• Bristlecone pines have a limited growing season
  of only one or two months per year.

• This produces narrow rings which are very
  sensitive to climatic variations.

• By crossdating between living and dead wood, and
  then between sub-fossil samples, a continuous
  master chronology has been developed which now
  extends back 8681 years.

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Dendroclimatology

• Dendroclimatolgy is the study of past climatic
  conditions using tree rings.

• It allows palaeoclimatic information to be
  precisely dated.

• When rings are very close together it indicates
  that there was not much water available for the
  tree, i.e. drought.

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Dendroclimatology

• Dendroclimatology enables deductions to be made
  about

• Variations in summer temperature
• Precipitation regimes
• Linkages between glacier behaviour and climate
• Relationships between climatic change and late
  Holocene volcanism.

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Autocorrelation

• The relationship between tree rings and climatic
  conditions can be affected by a lag time.

• Trees can store food reserves and water for a
  number of years and so the stored material could
  be used during adverse years.

• The width of a tree ring for a particular year
  is determined by environmental factors from both
  that year and previous years.

• A series of annual ring widths is autocorrelated
  using sophisticated statistical techniques.

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Bibliography

• Reconstructing Quaternary Environments by
  J.J.Lowe and M.J.C.Walker
• Geography An Integrated Approach by David
  Waugh
• Advanced Geography by David Redfern and Malcom
  Skinner
• www.sonic.net/bristlecone/dendro.html
• Presentation by Tom Cleverley