Where does the trunk end?

General discussions of measurement techniques and the results of testing of techniques and equipment.

Moderators: edfrank, dbhguru

Post Reply
User avatar
JHarkness
Posts: 245
Joined: Sun May 13, 2018 5:44 pm

Where does the trunk end?

Post by JHarkness » Fri Mar 08, 2019 10:01 am

With all of the volume modeling talk recently, specifically that of big crowned hardwoods, I want to ask the simple question, where does the trunk end and the crown begin?

Here is an example, I recently volume modeled a strange beech with a trunk that splits just 35-feet off the ground into over dozen tightly spaced skinny leaders that ascend all the way to 120'. The tree's total volume is 425.9ft3, but only 154.2ft3 is within its trunk, so how would one compare this with a more typically formed beech almost equal in overall dimensions including total volume, but with a massively different trunk to crown volume ratio? In the end, I think this comes down to where we determine that the trunk ends and the crown begins, perhaps me must develop a set of written guidelines for this so as not to skew data between different trees and different measurers? Something to think about.


Joshua Harkness
"Be not simply good; be good for something." Henry David Thoreau

User avatar
dbhguru
Posts: 4467
Joined: Mon Mar 08, 2010 9:34 pm

Re: Where does the trunk end?

Post by dbhguru » Fri Mar 08, 2019 10:22 am

Joshua,

You are spot on! This has always been the 800-lb gorilla in the room. So much of our conceptual framework about tree form has been guided by conifers and young apically dominant hardwoods. In NTS, we are poised to take a leap into the abyss driven by our desire to compute volumes and convert the results to sequestered carbon.

I hope Don and Michael Taylor and others will jump in. I think, for myself, I tend to choose the most vertical trunk-limb that makes it into the top of the crown when the path can be followed for volume modeling purposes. In the case of two equally qualified competitors to have a basis for comparison to more compliant forms, I may oll the dice. In the case of the big spreaders, I punt. Basically, this is new territory in terms of crown versus trunk, or more appropriately limbs versus trunk. But if we skip comparisons between radically different forms, does it matter? If we're looking for volume, we can acknowledge the shift from a short, squatty trunk followed by an explosion of limbs versus a single trunk supporting a modest spread of horizontal limbs. The place where we run into big trouble is where we are attempting to apply a trunk-center volume model that calls for a total tree height and a diameter at breast height and then projects trunk volume as thought there were a clear path to the top.

Bob
Robert T. Leverett
Co-founder, Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
Co-founder, National Cadre

ryandallas
Posts: 115
Joined: Fri Mar 07, 2014 5:23 pm

Re: Where does the trunk end?

Post by ryandallas » Sat Mar 09, 2019 4:41 pm

This reminds me of the question, "What is a shrub, and what is a tree?" Authorities have tried to provide specific numbers, but these seem arbitrary. So a tree is a woody plant over twelve feet tall--why not a woody plant over 12'3" tall? Or over 11'11" tall? And so on. A horticulturalist named Guy Sternberg offered a more impressionistic, common sense definition: a tree is a woody plant you stand under, and a shrub is a woody plant you stand beside. Maybe a similar line of thinking could be applied here, but I have never measured tree volume before.

User avatar
dbhguru
Posts: 4467
Joined: Mon Mar 08, 2010 9:34 pm

Re: Where does the trunk end?

Post by dbhguru » Sat Mar 09, 2019 6:59 pm

Ryan,

We use arbitrary cutoffs to form many definitions. Just one of those things.

Bob
Robert T. Leverett
Co-founder, Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
Co-founder, National Cadre

User avatar
JHarkness
Posts: 245
Joined: Sun May 13, 2018 5:44 pm

Re: Where does the trunk end?

Post by JHarkness » Sat Mar 09, 2019 9:25 pm

Ryan,

Now I've got a situation for you, I was hiking in the South Taconic Range recently where there is a lot of bear oak, but this species rarely grows beyond a human's height, yet they are very much trees in their form. In terms of trees vs. shrubs, I would call any sub-canopy woody plant that is naturally and commonly multi-stem (not coppiced trees, root sprouts, or any other multi-stem forms that result due to injury or stress) a shrub. But then there are always the weird ones, single-stem chokecherries, multi-stem gray birches and root-sprouting American bladdernut come to mind.

Bob,

I find your definition of where a trunk ends quite interesting, I wouldn't consider a vertical limb reaching the top of the crown a trunk unless it is clearly linked to a lower portion of the tree that can clearly be identified as the trunk. Your method certainly works for conifers and young(ish) hardwoods or those with clearly defined trunks (forest-grown tuliptree for example), but please consider the following photo.
IMG_9808.jpg
Which of the many small vertical limbs would be considered the trunk? To me, the trunk ends when there is no longer a vertical limb ascending into the crown (or a non-vertical limb that is clearly an extension of the trunk) above a major point of branching, on some trees this point is clear, on others it isn't evident and may not exist at all. If a trunk splits into multiple leaders, I would consider the leaders part of the trunk unless they are not-near vertical, are very small, or are too many to determine which one(s) is an extension of the more clearly defined trunk lower on the tree. I also like to think about how sharply a limb turns off of the trunk, the sharper the turn, the less likely it can be considered the trunk, so if a trunk splits into two limbs at a very shallow angle, I would probably consider them part of the trunk, but if they split at a very sharp angle, I would include them with crown volume. Consider the following diagram as an explanation of my definition of 'where the trunk ends'. Please excuse the poor graphics skills.
TrunkDefinitionsDiagram.png
Joshua
"Be not simply good; be good for something." Henry David Thoreau

User avatar
dbhguru
Posts: 4467
Joined: Mon Mar 08, 2010 9:34 pm

Re: Where does the trunk end?

Post by dbhguru » Sun Mar 10, 2019 10:39 am

Joshua,

Actually, I agree with you. I wasn't clear. My system is merely to create a kind of parity with true single-stem trees when applying the FIA allometric equations. In terms of calculating actual volumes, we really have no alternative to mapping out the limb architecture and dealing with it as it actually exists as opposed to idealizing it. And I think the latter will be increasingly important as we try to better determine annual growth increases for urban trees that appear stagnant to the causal eye.

Bob
Robert T. Leverett
Co-founder, Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
Co-founder, National Cadre

User avatar
Erik Danielsen
Posts: 855
Joined: Mon Mar 17, 2014 5:46 pm

Re: Where does the trunk end?

Post by Erik Danielsen » Sun Mar 10, 2019 1:07 pm

I've been thinking about this as this discussion has gone on, as it's a question that's been raised before... deferring to the fact that biologically there is no hard line we can rely on to separate trunk from crown or shrub from tree, not like we can monocot vs dicot or plant vs mammal- the main value of the definition should be its practicality as a conceptual tool to facilitate our investigation of the questions at hand.

In that sense, perhaps it doesn't make sense to try to consider the architecture of trees that have a dominant central axis (as in both the conifer and young hardwood examples in your diagram) in the same terminology as we consider the architecture of trees that no longer have a single dominant central axis from base to peak, which is true of pretty much all older hardwoods (and sometimes older conifers) even if one branch within the crown is more or less vertical over the true trunk. Is there an essential, irreducible difference to their realities? No, not really. But is there a difference in the resulting structures? Yes, at least to my observations. Sometimes even very large hardwoods coming into maturity are still dominated by a single axis from base to peak, often sycamores or tulips, that might have compatriots of similar dimensions and age that are nonetheless very different in structure. Would maintaining definitions of crown vs. trunk that are subject first to whether a tree is or is not dominated by a single central axis make the situation easier to work with? I'm starting to think so. At least if we want to build our datasets in ways that can be useful in the future for developing superior models.

Does anyone agree? And if so, what are your thoughts on refining that concept?

User avatar
JHarkness
Posts: 245
Joined: Sun May 13, 2018 5:44 pm

Re: Where does the trunk end?

Post by JHarkness » Sun Mar 10, 2019 1:30 pm

Erik,

I fully agree. I've really started thinking more about what is a trunk, where does it become a limb, and how that, and person to person variations, affect our volume modeling. How can we compare trunk to crown ratios if we don't have a set definition of where a trunk should no longer be considered a trunk or any guidelines for a measurer to follow? The biggest issue with this in my mind, is variation between measurers on what parts of a tree should be modeled as a trunk or as limbs.


I'm considering going around and taking form photos of hardwoods of varying sizes and ages and using that to at least assist my own decision making when volume modeling.


The other question we may need to ask ourselves is "does it really matter?" As you pointed out, there is little to no biological difference between the trunk and limbs. In a perfect world, perhaps we should only focus on total volumes of trees instead of trunk and crown volumes? But trunk and crown volumes individually have their own purpose, so I do think we need to continue using them, but perhaps we should not take them quite as seriously as a total volume?

Just a few thoughts,

Joshua
"Be not simply good; be good for something." Henry David Thoreau

User avatar
Erik Danielsen
Posts: 855
Joined: Mon Mar 17, 2014 5:46 pm

Re: Where does the trunk end?

Post by Erik Danielsen » Sun Mar 10, 2019 1:53 pm

I'm thinking similarly about making a point of documenting those different forms. In regards to your last thought- I do think that it potentially matters a lot, in the context of developing better models. If we find that on average there is a predictable difference between the volume of individual trees with a dominant central axis vs. a crown/trunk dichotomy even when species, dbh, and height are otherwise more or less the same- that's something important to be able to account for.

User avatar
Don
Posts: 1560
Joined: Tue Mar 09, 2010 12:42 am

Re: Where does the trunk end?

Post by Don » Sun Mar 10, 2019 2:49 pm

Josh, Eric-
Bob and I struggled with this "Where does the trunk end?", while working on the Measuring Guidelines. I think you're coming to grips with a solution for the problem you're facing and it's looking productive!
Some of the citations that went towards the solution to the problem we faced "Single- or Multiple-stemmed tree(s)" follow:

LITERATURE CITED
Brown et al, 1967. Apical dominance and form in woody plants: A reappraisal. American Journal of Botany 54:153-162.

Del Tredici, P. 2001. Sprouting in temperate trees: a morphological and ecological review. The Botanical View 67: Pp. 121-140.

Gschwannter, T., K. Schadauer, C. Vidal, A. Lanz, E. Tomppo, L. di Cosmo, N. Rober, D. Englert Duursma, and M. Lawrence. 2009. Common tree definitions for national forest inventories in Europe. Silva Fennica 43(2):303-321.

Halle, F. 1999. Ecology of reiteration in tropical trees. Pp. 93-107 in M.H. Kurmann and A. R. Hemsley (eds.), The evolution of plant architecture. Royal Botanical Gardener, Kew, London.

Ng, F.S.P. 1999. The development of the tree trunk in relation to apical dominance and other shoot organizational concepts. Journal of Tropical Forest Science 11: 270-285.

Putz, F.E. and R.R. Sharitz. 1991. Hurricane damage to old-growth forest in Congaree Swamp National Monument, South Carolina, U.S.A. Canadian Journal Forest Resources 21: 1765-1770.

Sakai et al. 1995. Adaptive significance of sprouting of Euttelea polyandra, a deciduous tree growing on steep slopes with shallow soil. Journal of Plant Resources 108: 377-386.

Sutton, R.F. and R. W. Tinus 1983. Root and root system terminology. Forest Science Monographs. 24:137.Hoadley, R.B. 1980. Understanding wood. The Taunton Press, Newtown, Connecticut, pp.29-32.



Some of the conclusions we drew, can be found in the AF Measuring Guidelines on page 74:
[url]http://www.AF-Tree-Measuring-Guidelines_LR[/url]

but basically, after a survey of national and international papers on this topic, there is a wide array of views, none of which approach a universal concise definition. I think that you two are on the right track for your current project...I've highlighted in brown, the citation that may be of the most use, but others may also help.
-Don
PS:I think Bob and I fully appreciate your efforts at graphical representations of tree forms!
Don Bertolette - President/Moderator, WNTS BBS
Restoration Forester (Retired)
Science Center
Grand Canyon National Park

BJCP Apprentice Beer Judge

View my Alaska Big Tree List Webpage at:
http://www.akbigtreelist.org

Post Reply

Return to “Measurement and Dendromorphometry”