|
Analysis of the Hentland
Churchyard Yew by David Lovelace
|
|
Planting date |
Woolhope Club |
LOWV |
|
Date |
1605 |
1868 |
2005 |
|
Interval years |
|
263 |
137 |
|
Girth, feet |
|
12 |
14 |
|
Girth, inches |
|
144 |
168 |
|
Girth, mm |
|
3657.6 |
4267.2 |
|
Radius, mm (divide by 2 x Pi) |
|
582.1 |
679.1 |
|
Difference 1868 to 2005 |
|
|
97.0 |
|
Mean ring width 1868 to 2005 |
|
|
1.41 |
|
Age by linear extrapolation 2005 to 1868 |
1524 |
|
481 |
|
Mean ring width from 1605 to 2005 |
|
|
1.70 |
|
Mean ring width from 1605 to 1868 |
|
2.21 |
|
Taking the Woolhope Club measurement and their planting date
(1615 + their assumption of the tree being 10 years old when
transplanted) gives a mean ring width of 2.2mm. Our
measurement comparing with that of 1868 gives 1.4 mm, which
can be interpreted as the growth rate slowing with age due to:
senescence, shading by adjacent trees and/or
pollarding/pruning. These figures are consistent with the few
published records:
A yew tree recently felled to protect the masonry at West
Horsley, Surrey allowed a detailed analysis of its rings
showing a mean ring width of 2.8 mm for the 1st 100
years and 0.9 mm for the next 210 years (see
www.tree-ring.co.uk).
There is a large variation of ring width with age reported
from one of the few publications on the subject (Tabbush and
White, Quarterly Journal of Forestry, July 1996 pp
197-206, 'Estimation of Tree Age in Ancient Yew Woodland at
Kingley Vale') namely 3.5mm for early growth down to 0.051 for
older trees, a factor of 70.
Given this uncertainty, the simple extrapolation from our
single measurement which extended the age from 400 to 480
years and equivalent to a 20% error is actually quite
reasonable.
Tabbush and White published a formula relating the final ring
width to age which obviously requires a small coring –
something which we might (with permission) carry out? However
this assumes a known variation of ring width with age and an
accurate measurement of final ring width
I am sceptical of this method for at least one reason namely
that the corrugated cross section of a yew butt means that a
single measurement is inherently unreliable. Rings can even
disappear a some points around a Yew tree’s circumference
which would, according their formula, mean an infinite age. No
wonder stories of 4000+ year old yew trees proliferate | 
