core data vs. stand age
  Jul 02, 2005 09:27 PDT 

Quick question for the ENTS brain trust...

I know that quite of few of you have used core data in your research, so I'd
like to get some advice on using cores taken at or near breast height to
estimate the true ages of trees (they obviously don't burst onto the scene at
1.2 m tall!). Are there any accepted conventions to account for growth to BH, or
is it preferred to report age at BH as I've seen some authors do. Thanks!

Re: core data vs. stand age   Don Bertolette
  Jul 02, 2005 12:57 PDT 


Most of the land management agencies I've worked for developed species
averages for the number of years to breast height...for a wide range of
coniferous species in the west, depending on location, this could range from
6-10 years.

I would guess that eastern hardwoods would be more variable and take more
years...I don't recall in my time in Kentucky what
species/age-to-breast-height factor was used.
Personally I think a variable diameter, portable MRI for the woods machine
would be a boon to those of us charged with aging trees.

Re: core data vs. stand age    Neil Pederson
   Jul 02, 2005 14:48 PDT 


It is probably best to stick to age at coring height. The reasons
are similar to the ones Charlie Cogbill outlined in estimating tree
age from diameter - second post on this page:

The amount of time for a tree to reach coring height in a
closed-canopied forest would vary widely depending on a species
competitive abilities in the understory, the ability of that tree to
compete in the understory [certainly there is some kind of genetic
variability within species], and the disturbance history around each
particular individual. The local disturbance history is probably most
critical factor.

Models have been created to estimate the time to reach coring
height. The best paper I am aware of on this subject is: "R Villalba,
TT Veblen. 1997. Regional patterns of tree population age structures
in northern Patagonia: climatic and disturbance... Journal of
Ecology". Ricardo actually cored trees at root collar height as a
part of this study. His model was successful because the ecosystem he
was working in was semi-arid to arid. The trees, therefore, were
widely scattered and there was little, if any, tree-to-tree
competition. It is this kind of competition that reduces the ability
to produce an accurate estimate of time to reach coring height. It
would seem like you would only introduce more uncertainty into the

Here is a search link with references related to Ricardo's paper and
your question:

I recall another study in Quebec looking at ages at coring height vs
root collar height in a post-fire black spruce forest. Again,
tree-to-tree competition in this situation would be considerably less
than in a closed-canopied forest. The differences in ages at coring
height was at least up to 5 years, and, IF I recall correctly,
perhaps up to a decade.

Charlie's last paragraph on the ENTS page above probably sums up the
situation best:

"Of course much of this is argument is about statistics and they
can easily mislead, but I am convinced that age cannot generally be
derived by extrapolations or predictive relationships. This is the
basis of my "second rule of forestry" that "one cannot tell the age
of a tree by its size". Since there are direct means of deriving
tree ages and more importantly the age structures of stands, I
encourage not compounding the errors by secondary methods. Thus I
am interested in any actual ages you might have found in the Zoar
Valley. However scanty, these are the appropriate data that are
needed for the description of the age structure of this site."

Hope this helps,
Re: core data vs. stand age   Lee Frelich
  Jul 02, 2005 16:44 PDT 


With the types of trees and conditions you have in Zoar valley and you
other study sites, the time to grow to 1.2 m could be 5, 10, 20 or 50
years. Even if you had the ring count from the base, many of the trees
would have been suppressed and have a lot of missing rings, and suppressed
ring sequences are very hard or impossible to cross date.

You are measuring forest age structure and disturbance history at 1.2 m
above the ground, so report it as such, and quit worrying about total age
(which isn't even very interesting in the types of forest you work in,
compared to dates of release from suppression and early growth rates for

RE: core data vs. stand age   Will Blozan
  Jul 02, 2005 18:36 PDT 

Don't bother with age to BH (1.37 M actually...) I have aged hemlocks to 80
years @ 1.37 M tall- I am sure they can be older. I also aged a sugar maple
to 40 years @ less than 1 M tall. Ground level is not convenient! I would
say most literature is based on age at BH, including all the Smoky Mountain
and Chattooga work I did. Perhaps basal age is relevant in some cases, but
may not reflect "functional" stand age.

Core data
  Jul 02, 2005 20:25 PDT 

Thanks all...

Sounds like you're confirming my impression that age at coring height is the
best way to report data. I agree with Don that an MRI machine would be nice.
BTW, I'll report a few ZV age highlights over the next few weeks. Thanks again.