Dendrochronology

Dendrochronology
Introduction
Tree rings can be used for reconstructing past climate because trees are good environmental indicators. They produce very small rings during years of drought and large rings during years of good growing conditions.
By counting the rings from the middle of the trunk, and studying the width of the rings, scientists can reconstruct an approximate calendar of wet and dry years. It is assumed that the weather affected ancient tree ring growth the same way it does today. It is also possible to date the occurrence and frequency of fires by finding scars that appear in the growth rings.
Characteristic Of Tree Components
Trees go through annual cycles of growth. Roots are busy in the early spring and late autumn. Leaves and twigs grow in spring and the tree adds wood all summer long.

A years growth on a tree ring.
Cross-section of trunk showing: bark; cork cambium; cambium; phloem; xylem and pith.
Schematic cross-section showing features
Why do ring widths vary?
Variability of tree ring width and climatic conditions relates to two sets of seasonal patterns:
Early wood grows as large, thick-walled cells
Late wood grows as small, densely-packed, thin-walled cells
Early wood + late wood = an annual growth ring
The average (mean) width of both parts of the tree ring is dependant on:
tree species
tree age
availability of stored food
climate (precipitation, temperature, humidity, sunshine, windspeed and humidity).
Two kind of tree sampling for dendrochronology measurement
TREE SLICE SAMPLING
Collection of the tree slice
Tree slice surface preparation by polishing
Choice of the suitable part of tree slice for dendrochronology measurements.
TREE CORE SAMPLING
Uses an Increment borer
Generally confined to standing trees or structural timbers


TREE SLICE SAMPLING
TREE CORE SAMPLING
TREE RINGS MEASUREMENT
Each tree should be measured at least in two radiuses.
The final results is mean from each radius of adequate tree ring measurement
TREE RINGS MEASUREMENT
TREE RINGS MEASUREMENT
Building a Chronology
For any investigations of climate condition changes in the past, or other applications, a master chronology must be prepared.
This allows us to match the measurement of tree rings width to fixed calendar years.
Building a Chronology
Applications of Dendrochronology
Dendrochronological data is used in various types of research:
Dating
Climate
Studying climatic highs and lows (so-called catastrophes)
Recently, dendrochronological data has been used to establish the provenance of oaks by comparing the growth patterns from different areas and establishing where the oak originally grew.
Calibration of Radiocarbon Curve
This was done by dating samples of known calendar age and plotting the results.
Dating
Corlea,Co. Longford
Dated to 148 BC
Dating
Navan Fort, Co. Armagh
Dated to 95 BC
NavanFort
Prior to excavation its date was uncertain, but now it is known that the main mound and enclosure date to 95 BC.
Navan Fort
The date came from the base of a large oak post in the centre of the main site.
DanishOak Coffin Graves
Burials below mounds include well preserved organic materials including coffins.
This has allowed for a detailed chronology to be built for the relevant period.
Danish Oak Graves (1450-1250 BC)
Map showing the location of dendro-datedgraves in Denmark (note wide distribution)
Provenancing
The Vjeby ship (shown here) was found off the coast of North Zealand, Denmark, in 1976 and has been dated by dendrochronology to 1372.
The source of the oaks timbers could be narrowed to the region around Danzig/Gdansk. Data from other boats has suggested a strong ship building industry in this area.
Provenancing
Viking boats from Roskilde fjord can be shown to have been built with Irish timber.
This was the basis for the Sea Stallion project last summer (still on display in Collins Barracks).
Climate Studies Using Dendrochronology
Accurate written records for temperature only go back for 150 years or so?
How do we understand long term climate change?
Climate Studies Using Dendrochronology
We can combine our other data to produce longer sequences, such as tree ring data, ice cores and some historical records
1628/9 BC
This is the growth pattern from a number of trees from a County Antrim Bog.
The areas in black is the narrowest growth rings – all in the 1620s BC.
Was this a period of intense cold??
1159 BC
Many Irish bog oaks have a sequence of around 18 narrow rings between 1159 BC and 1141 BC (red arrows).
Does this equate to a period of intense cold??
How would this affect contemporary society?
10th Century BC Narrow Ring Event (948 BC)
In some cases sites can be shown to be built to coincide with poor tree growth.
This shows bog oak growth relative to dated sites (1100-800 BC).
Catastrophes?
Some people maintain that these environmental events coincide with significant cultural and historical events.
Main work is by Prof. Mike Baillie:
Exodus to Arthur
A Slice in Time.