UKTC Archive

RE: Estimating tree ages based on trunk diameter/girth

Subject: RE: Estimating tree ages based on trunk diameter/girth
From: grumpy
Date: Jan 12 2022 11:50:15
Paul

You already have a reference to "Mitchell". No doubt someone will point out 
"White" shortly. Neither were mensurationists or statisticians, although 
clearly both collected loads of data. I frankly am appalled by what I read 
and hear about tree age and diameter.

I realise most of us need a good old beard to stroke (sorry, ladies) when we 
are asked how old a tree is. We stroke our beard (I don't have one) to 
impress on our listeners how much thinking we are doing and how much 
experience we are recollecting when we examine the size of a tree and come up 
with a number. Ooooo this one must be at least 200 years old, I say. Gasps of 
adulation arrive and we all go off happy, respectful of this ancient tree. 
It's frankly nonsense:

Trees vary considerably in their diameter growth. Partially determined by 
species, partly determined by site, partly determined by density. The latter 
simply acknowledges that competition from nearby vegetation and trees alters 
growth rates - closely growing trees will fatten less quickly than free 
growing trees. Yes obvious in a spacing trial in early years, but less 
obvious with widely grown trees when they are large. 

The situation was acknowledged in Forestry Commission Bulletin No 1 dated 
1919 Collection of Data as to the Rate of Growth of Timber.

We all know that weather and climate alter growth, so attempting to have a 
figure for all species in all conditions is well.......an average. It's of 
very little use in determining age of individual stands, and in particular 
individual trees. If someone were to bring this into a court room, I would 
have a field day.

Yes, it would be nice to have a simple solution to a complex problem. The 
solution is to kick councils up the backside and say 50 year old, or even 20 
year old Area orders are unworkable......and if you want to prosecute people 
for tree works to marginally aged trees you may have a problem. I realise you 
have a practical problem in front of you, but there is no easy answer. You 
are better off trying to find old aerial photos from the second world war (or 
more recent if that is the age of the TPO)

Before someone does mention "White" look at his FC Information Note dated 
1998. Table 1a sort of acknowledges the significant variation in growth rates 
possible. But without some sight of the data on which this table is based or 
any analysis arising from it you could get seriously misled. All of the 
figures are averages. Thus expectation that growth might be greater on a 
"good" site than on an "average" site doesn't help much. Poorly growing trees 
on a good site are likely to grow less than fast growing trees on an average 
site. Using these to estimate the age of trees using these averages is as 
good as stroking my beard......

A good source of tree growth data? The only source is Forest Research but 
clearly their data is almost entirely for plantations & forest species. I 
doubt they have much data on widely spaced trees and even less on open grown 
trees. I wonder whether they hold Mitchell's and White's data and whether it 
was approved for professional use (i.e. anecdotal data doesn't stand up to 
much scrutiny), or just binned?. Zero data on the wider range of trees used 
in arboriculture? I approached them a little while ago to see if they have 
any data on yew growth. Zero was the reply. You can find a synopsis, but no 
growth data in a paper in the RFS QJF in early 2021 or late 2020. I am afraid 
I don't have the specific reference to hand but I think it contains 
"Permanent Sample Plots" in the title. Richard Baden came back to me with a 
very long email & you could explore what data they have, but Richard's remit 
may be limited to the plots: 

Richard Baden         (email using @forestresearch.gov.uk) 
Assistant Sample Plot Officer
Forest Mensuration, Modelling and Forecasting
Forest Research
Alice Holt Lodge
Farnham  GU10 4LH

They may have a dusty cabinet of growth data that no-one has looked at for a 
while. That's always the impression I get when I go to Alice Holt.

Jon


-----Original Message-----
From: uktc-request@xxxxxx.tree-care.info <uktc-request@xxxxxx.tree-care.info> 
On Behalf Of Paul Barton
Sent: 12 January 2022 08:56
To: UK Tree Care <uktc@xxxxxx.tree-care.info>
Subject: Estimating tree ages based on trunk diameter/girth

Dear collective,

I wonder if you can help me?  I am looking for a simple method to estimate 
tree ages as part of a preliminary review of some area TPOs - i.e. to assess 
whether trees that are present now were most likely present (or not) on the 
year the area TPO was served.

I have come across various apps that claim to give an age based on trunk 
girth but after a brief test they seem to overestimate age (based on my 
experience only) as I suspect they are based on forestry plantation trees 
which tend to be more slender over time than open grown trees.

I came across this document from Newport council 
(https://www.newport.gov.uk/documents/Leisure-and-Tourism/Countryside/Measuring-Trees.pdf)
 which suggests that tree growth rates could be split out in to slow, 
moderate and fast - each with a corresponding ‘average’ annual girth 
increase.  These are given as:

• Slow - 1.88 cm per year
• Average - 2.5 cm per year
• Fast - 3.13 cm per year

Using such values would allow me to classify species by growth rate category 
and therefore have a ready reckoner to estimate tree ages based on their 
girth.  It can never be claimed to be very accurate but for the purpose of 
quickly assessing hundreds of trees a repeatable documented method would be 
useful.

BUT I don’t know if the above growth rate values are based on good data, 
ideally in the UK.

Finally to the point (congratulations if you lasted this long)…can anyone 
point me to a reliable source of UK tree growth rate data so that I could 
verify or amend the above suggested rates of growth?

Kind regards,

Paul Barton

www.barton-hyett.co.uk | Barton Hyett Associates Ltd | Arboricultural Experts





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