1. DENDROCHRONOLGY

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

11. 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.

12. 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.

13. Dendroclimatology Dendroclimatolgy is the study of past climatic conditions using tree rings. When rings are very close together it indicates that there was not much water available for the tree, i.e. drought. It allows palaeoclimatic information to be precisely dated.

14. Dendroclimatology Dendroclimatology enables deductions to be made about: i)Variations in summer temperature ii)Precipitation regimes iii)Linkages between glacier behaviour and climate iv)Relationships between climatic change and late Holocene volcanism.

15. 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.

16. 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