QMT Features: August 2014
Counting the rings
Researchers are using a Heidenhain linear encoder and DRO to date and understand ancient timber

A team at Manchester Metropolitan University is using the study of growth rings in timber to accurately date ancient specimens (dendrochronology) and gain insights into pre-historic environmental conditions.

Work at the University’s Division of Geography & Environmental Management by Dr Jonathan Lageard has, for example, dated  one oak tree sample to 4189 BC adjacent to the Ribble Estuary, permitting an investigation of a precisely-dated ‘bog oak’ woodland layer and its demise. 

Using a custom-made inspection rig based on a Heidenhain LS 403 linear encoder linked to a single-axis Heidenhain ND 280 DRO, tree samples are placed on a simple measuring stage under a binocular microscope. 
The distance between each ring/ring boundary (from the start point - the sample’s centre) is then accurately calibrated using the high-accuracy glass scale linear encoder. The measured data, which is displayed on the DRO, is transferred to a PC in real-time (via the DRO’s USB connection) as each ring is measured.
The tree sample ‘discs’ – radial sections of the trunk taken using a chainsaw - are air-dried and polished using sandpapers of increasing grit size before being inspected on two radii. The PC and measuring stage are used to produce ring-width records for individual trees using a bespoke Input software package.  Dendro software can then be utilised to generate a mean ring-width record for the sample and further to make statistical comparisons between different tree-ring series, searching for similarity/contemporaneity.
“Trees from sites with similar environmental conditions tend to produce similar growth responses and these patterns are measured recording what effectively are each tree’s bar code,” says Dr Lageard. “Mean records for individual trees or averages for groups of trees are often cross-matched against reference chronologies held, for example, in the International Tree Ring Database in order to achieve a calendar or ‘dendro’ dates. Samples taken from different locations around Europe can have similar ring-width patterns signifying synchronous environmental events during the last 10,000 years and even back into the last ice age.”
Dr Lageard’s interest in dendrochronology began during his postgraduate studies at Keele University when he was tasked with taking pollen samples from peat bogs in order to reconstruct vegetation history. The identification and counting of the pollen grains helps create a picture of past vegetation and associated environmental conditions, ie finding and identifying different pollen types has revealed major temperature change (rise) 10,000 years ago as vegetation responded to post-glacial warming. 
The rig used today at Manchester Metropolitan University is based on similar principles as the one Dr Lageard was using in the early ‘90s. The set-up was devised and developed by leading dendrochronologist Ian Tyers (then of The Museum of London and currently an independent consultant) in conjunction with Martin Bridge (then of the City of London Polytechnic  and currently affiliated to the Oxford Dendrochronology Laboratory and University College London). 
In those days, the rig also utilised a HEIDENHAIN encoder and DRO but was linked to an Atari ST computer running the Input and Dendro software. The complete set-up has been recently updated with the LS 403 encoder and ND 280 DRO by HEIDENHAIN authorised distributor C & H Precision Measuring Systems, which also integrated the hardware with the PC.
Although used by Dr Lageard for a series of straightforward measuring tasks, the ND 280 also features numerous functions for measuring and processing individual positions - for example, for sorting and tolerance check mode, minimum/maximum value storage and measurement series storage. www.heidenhain.co.uk 
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