Facts and Figures
click on the Facts & Figures to find out how we measured and recorded them
Tree age: about 160 years old - to be confirmed
We know from the estate records of Blenheim Palace that the trees in the plantation containing the OneOak tree were probably planted in the 1850s.
Once that the tree is felled we will be able to use dendrochronology or tree-ring counting to provide an exact date.
Read about this work
here.
Tree Height: 23.9m
Tree height was calculated using trigonometry from measurements taken using a hypsometer – a type of clinometer.
In the photo below you can see Ian, a scientist from Forest Research, using the hypsometer.
If you look carefully at the screen of the hypsometer you can see the distance to the tree (D) is 36.3m, and there are three different readings for height (A).
The hypsometer has already worked this out because an internal sensor calculated what angle (a) was.
Ian knew that height (B) was 1.3m (because he could easily measure this).
So the total tree height was A (22.6m) + B (1.3m) =
23.9m.
Stem diameter: 89.9cm
The stem diameter of trees is always measured 1.3m above the ground – this is called
diameter at breast height (dbh).
It is possible to calculate the diameter if you use an ordinary tape measure to record the circumference (diameter = circumference / π).
Foresters use a diameter tape, which is marked with this calculation built in. Here you can see Ian measuring the dbh with a diameter tape.
We now know our tree has a dbh of
89.8cm.
Crown diameter: 17.8m
We stood underneath the tree and using a clinometer to sight vertically upwards into the tree’s crown, we stood exactly under its outer edge. We then measured from this point to the tree stem. We did this at eight different points around the tree.
When these are plotted on a graph, it is interesting to observe that our tree had a much smaller canopy on its northern side.
This will be because the tree will have had much less sunlight on that side.
By adding the eight crown radius measurements together and dividing this number by eight, we can calculated that the average canopy
radius is 8.9m.
If we double this figure, then the average crown
diameter is
17.8m.
Timber height: 12.9m
Using the same techniques as for the tree height, we have measured the timber height at 12.9m.
How did we know where to measure to? Using an experienced forester’s eye!
Looking carefully at the tree it is possible to see where the main stem bends and becomes too branched.
Beyond this point it would not be possible to cut straight timber from the tree.
Timber volume: 4.96m3
It is important to estimate how much timber we may be able to harvest from the tree.
If you wanted to do this accurately you would need to use the formula for the ‘volume of a truncated cone’ which is V = 1/3 * π * ( R12+R1 * R2+R22 ) * h !!
The maths is not as hard as it looks but the main problem is that R2 refers to the radius of the stem at the top – i.e. 12.9m up the tree and we don’t know that.
Foresters have developed some clever charts that make it possible to estimate volume from just the stem diameter (dbh) and timber height – and we know both those values.
The Forestry Commission ‘single tree tariff chart’ for oak tells us that with a dbh of 90cm and a timber height of 12.9m the OneOak’s timber volume (‘overbark’) is 4.96m3.
Leaf Area Index
After taking the spectacular images of the tree canopy with the hemispherical camera lens (see
blog post of September 18th), Forest Research scientists then used special software to calculate how much of the sky was visible underneath the tree in this image.
The second image shows a screen shot of the software being used on the same image.
Leaf Area Index or LAI is the ratio of total upper leaf surface of vegetation divided by the surface area of the land on which the vegetation grows (
read more ). Forest Research calculated that the LAI for OneOak was
1.4.
LAI values can range from 0 (no cover) to 6 (dense forest cover). Apparently our result of 1.4 is quite low for a mature broadleaved woodland. Scientists will now use this value in future calculations of the tree’s biomass.
Tree weight
Not yet known
Tree volume
Not yet known
Biomass
Not yet known
Carbon content
Not yet known
