Trunks vs limbs vs branches vs twigs    Robert Leverett
   Sep 26, 2005 05:28 PDT 


   The off-list discussion that we've been carrying on is much too
fascinating a discussion to continue off list. So let me introduce it
into the list. First a quote from your off-list e-mail: "I am concerned
that a higher branch might come off after a fork, or multiple forks of a
tree. This branch would provide the greatest offset from the center of
the tree base, but would not be the
farthest laterally from its point of origin on a secondary trunk. Also
I see problems about where you would define the beginning point of a
limb. Is it the same limb before that last fork, or are two new limbs
created at each split point? What if one fork is much larger than
another? Is this a side branch or a separate limb?"

   With respect to where to set the limits if a limb for measurement
purposes, you raise some very interesting points, some more toward the
aesthetic end of the spectrum, i.e the visual appeal of a limb
structure, some toward definitional, i.e. what is a trunk versus limb,
etc., and some toward the mechanics of measurement of whatever.

    Let's see, we have trunks, limbs, branches, and twigs. Who has the
definitions? Just looking at the bifurcations, it can seem relative. On
a white pine, limbs appear distinct from branches because I presume that
the genetics that produce each cause one to grow straight and the other
curved (Lee, any guidance here for us?).

    Where limbs take on the role of a trunk for a white pine, courtesy
of the little weevil, the result is distinguishable to the eye because
of the wiggly appearance of the limb(s) taking on a trunk role.

    It appears to me that each species has its distinctive
characteristics in terms of how it commonly branches and shapes itself
in open grown environments versus close quarters. It is just that the
combinations go through the roof. However, we can have lots of useful
discussions on this topic, with measuring conventions woven in.

   In terms of what is the length of the "longest limb", if we're
thinking in terms of the longest stretch of a limb before a major
branching (yes, I know, what is major?), then we have no really
practical way to get the multitude of measurements that would be needed
to answer the question. We look for a convenient beginning point and a
visible ending point. Practically speaking, this means we find the point
of separation of what looks like a limb from what looks like the trunk
and go to the end of the "limb structure". Depending on how angled the
structure is, we can choose different structures to get the greatest
lateral spread versus the greatest linear distance from beginning to

    The process of deciding where a limb structure starts (or ends), is
somewhat like following a named stream to its headwaters. At the river's
mouth, it sounds simple in concept. But along the way side streams
appear and join the named stream. What if a side stream is as large as
the main stream? The Colorado river system is an example, particular as
it relates to the point of entry of the Green to the Colorado. At the
point of entry, if one follows the Green to its headwaters, one gets a
longer river complex than following the branch that retains the name of
Colorado. Sometimes geographers, cartographers, and statisticians follow
one convention for naming one river system and another for another.
Interesting stuff. Who has some thoughts on this.

    In the case of the limb structure, nothing is named, so we're not
forced to follow what looks subordinate at a branching point. However,
if length is what we seek as opposed to lateral spread, Oh Boy, we're in
for lots of work.   


Robert T. Leverett
Cofounder, Eastern Native Tree Society
Limb Segment Length Determination  Robert Leverett
29 Sep 2005

Hi All,

The attachment hopefully speaks for itself. I've been toying with least effort methods for computing limb segment length from the ground. I'm considering limb segment length as the linear distance between two points on a limb structure. There may be a quicker way to do the job than what I show in the attachment, but I haven't thought of one. Finding the point on the ground directly beneath the end of the limb segment is unavoidable.

Limb Segment Length Determination diagram

Roots, trunk, limbs, branches, twigs   Robert Leverett
  Dec 21, 2005 06:21 PST 


Your comment about buttressing being part of a tree's root structure
reminded me of the terminology we use in defining the woody parts of a
tree. A question to those out there with knowledge of tree biology such
as John Kreslick, Jr. is when does a limb become a limb, branch, a
branch? In cases where you have a long straight trunk and relatively
short curved limbs extending out more or less perpendicularly, it all
seems clear. But in hardwoods, as we all see, the variations are
endless. In the case of oaks, I see what appears to be a continuation of
the "main" trunk with a second trunk/limb curving slightly outward and
then continuing upward to do its own thing.

   I've always assumed that genetics decides whether we have clearly the
continuation of a trunk or the start of a limb. But how settled is the
physiology? I've always assumed that the substitution of the term branch
versus limb spikes to the continuation of a structure.

    Anyone care to share the knowledge? Lee? John?

Re: Roots, trunk, limbs, branches, twigs   The Darbyshires
  Dec 21, 2005 19:51 PST 

There have been some studies that show that branches are inferior to main
stems in terms of hydraulic conductivity - i.e. main stems conduct more
water in the same amount of time versus branches. So, in times of drought
stress, it's more likely that a branch will die off versus the main stem.
Also, the farther out the branch you go, the lower the hydraulic
conductivity, so branch tips are more likely to die off when water is
restricted versus the base of the branch.

RE: Roots, trunk, limbs, branches, twigs
  Dec 22, 2005 07:11 PST 

I think that the structure of a tree is based more on environmental conditions than genetics. The amount of light, and nutrients. Trauma to the tree as it grows changes the course of which way and how it grows. Ultimately the tree that is damaged in it's younger years seems to have less of a chance of survival to a great age. Here at work, in the woods, I get to watch things happen. Often a small tree will be beat up by a male deer. Sometimes it will die outright, other times it is disfigured and continues to grow. It is no longer a single stem specimen, but may have an odd shape. If a limb falls from a larger tree and strips branches off a smaller tree, then that tree seems to focus energy to the healthy parts of it's system. This too will result in an atypical form. Often times in nursery stock the leader will die back to a point, but not kill the tree. It seems that the tree will cut it's losses and send out another leader when the conditions improve. There are millions of scenarios that change the structure of a tree that are environmental.

If a tree was grown in a controlled space, without outside interference, I wonder if all tulip poplars would have the same habit (or any species)

I do see genetic differences in trees also. Just yesterday a saw a red oak that was about 10"DBH that had a solid line of buds around about 1/3 of the root flare. I looked up at the tree to see many clusters of odd buds that didn't seem to be growing. I wondered if it was a genetic or environmental oddity.

How diverse do you think the genetic makeup of a species is in a location? Is it more harmful or helpful to introduce plants of the same species from a different genetic pool? I think it is better for humans to be less genetically similar, but what about trees? Is it a case where over tens of thousands of years a genetic strain becomes dominant due to survival of the fittest? Does that in turn make them more susceptible as a group when a new threat is introduced (HWA)?

I hope some of the science-types will chime in, as I would love to hear about research that has been done in these areas. Questions I have had for some time.


RE: Roots, trunk, limbs, branches, twigs   Robert Leverett
  Dec 22, 2005 08:51 PST 


   Good points, good information, and intriguing questions. Nowm where
are the tree biologists when we need them. I certainly agree that
environmental influences constantly shape and reshape tree form. But it
would be interesting to see if those most knowledgeable about tree
genetics would draw an ideal or range of ideals for each species with
which they are familiar. How would the perfect tuliptree look - if that
is even a sensible, relevant question to ask. In the case of
pencil-straight white spruce trees, it seems sensible, but with a white

   Artists drawing tree shapes for identification in tree books are
motivated by a kind of ideal in their minds. I have often looked at
young sugar maples in peoples' yards. There is a classic shape that I
see repeated. It seems archetypal. But as the tree gets larger and
older, the symmetry is reduced and the tree becomes more individualistic
and marked by the environmental impacts of storms, insects, etc.

   The question of what triggers the growth of a limb or limb structure
at a point along a trunk, apart from response to injury, intrigues me.
We know that forestry seeks to grow straight trees with long trunks and
does it by managing each tree's competiton. Maybe Russ Richardson,
Michele Wilson, and other foresters can come forward to describe the

   I'm waiting on Lee Frelich to offer some insights. He may be thinking
about this complex subject before responding. But when he does, I'm
going to be listening. Lee, lay some words on us.

Re: Roots, trunk, limbs, branches, twigs    John A. Keslick, Jr.
   Dec 23, 2005 18:39 PST 


In my words.

That is a very good question. It's a tough question. You got me thinking.
I just wrote a section on branches in my dictionary.

Branches grow from buds, sprouts grow from meristematic points. In roots,
which do not have buds, roots grow from meristematic points.

When Dr. Shigo started out with trees there were many books explaining how
to remove branches but none explained how branches come on trees. Most
publications, to my understanding, were promoting flush cuts. Flush cuts
meaning that the cut made was flush with the trunk thus removing the branch
collars. In a sense branch collars have small chemical factories that
resist the succession of microorganisms into the parent stem. The only book
I know of that explains how branches come on trees is "The World Wide
Punning Guide" by Dr. Shigo. If your library does not have it they can
order it from their website . I have the book listed
here. I cannot
emphasize how much understanding the latter book will offer.

Branches and Collars - When the parent stem is young, branches start.
Branches form branch collars and sprouts generally do not. There is
actually two collars at the base of a branch. The branch collar and trunk
collar are collectively called the branch collar. Where branches meet the
trunks of most trees, there will be a series of collars. Each year two new
collars will form. One is a trunk collar and the other is a collar which is
made up of branch tissues. Collectively we call them the branch collar.
These collars are what support the astronomical weight of the branch
(cantilever). Note, when looking at a tree from the outside, the two
collars are often spoken of as the branch collar, e.g., "do not remove
branch collars when pruning"   See "Branch Collar" at Dissections will show that the pith from the branch
will begin close to the pith of the parent stem. The pith is not an easy
pathway for microorganisms to travel because there is what I called a "Pith
Protection Zone" You must see the picture under "Pith Protection Zone" at

Branch Bark Ridge - The Branch Bark Ridges (BBR) is raised bark that forms
within the branch crotch. Codominant leaders may have a bark ridge.

Codominant Leaders. Codominant leaders are two leaders competing for the
sun. Be on the look out for codominant leaders that begin to grow downward.
They do not have a branch collar. A foreseeable failure. Codominant
leaders may have a branch bark ridge but in time the BBR may begin to turn
inward and we have what we call included bark. This can be referred to as a
weak union.

Sprouts - Are not branches. Climber beware. Sprouts are formed from
meritamatic points and do not have branch collars to support your weight.
However, on some trees they can form a collar. When pruning sprouts such as
epicormic, which means upon the truck, note that there is a swollen area at
the base. It's not a branch collar yet it is trunk tissue. Thus we should
not remove the swollen base. Dissections of sprouts will show that the
sprout is growing off the side of the trunk and the pith does not exist up
to a Pith Protection Zone in the trunk. Some trees sprout a lot, some
sprout when stressed. When a tree is cut and growth begins from the base of
the truck they are sprouts.

Flush Cuts Can Be Good - Not good for the single tree, yet working in a
group situation, a flush cut on a symplast supporting tree, will create a
hollow which can benefit small wildlife. Not good for the tree but good for
small wildlife.

I will try to follow through with these post. I would love to take a walk
in a forest and look at branch cores and such with you. Maybe that can
happen sometime. I am sure you have a great deal to offer me.

Also what happens when a tree falls and the branch or branches grow up.
What do we call them? I call some a harp tree

And some a "FOOT TREE" back in my swamp

Here is a "HARP TREE"


John A. Keslick, Jr.
Re: Roots, trunk, limbs, branches, twigs   John A. Keslick, Jr.
  Dec 24, 2005 05:46 PST 


Oh yeah, sprouts can also grow from callus on woody stem and woody roots.
Callus it what forms the first growing season about a wound. Now, callus
changes too woundwood by the next growing season. Woundwood is not
meristematic, callus is. That is why on some trees sprouts will grow from
new tissues about a wound. If you count how old the sprout is, you can tell
what year the tree was wounded because sprouts would have grown from the

Another note:
Branches form from preformed tissues in buds that produce stems and leaves.


Re: Roots, trunk, limbs, branches, twigs   John A. Keslick, Jr.
  Jan 04, 2006 14:59 PST 


About twigs. To me, twigs is a loose term. I use it so I will try to
define it. Again, you raised a great question.

Twigs would be small woody parts of branches and sprouts of stems.

BTW when a tree matures the leader buds abort. Then the side growth
continues thus leaving us with the flat crowns.

Limbs? I don't use the term much. Again I like to stick with branches,
sprouts and codominant leaders for stems. For roots - woody roots,
non-woody roots (absorbing), mycorrhizae, root hairs and there are many more
parts (connections) which I know exist.

Repeat - Stems can produce buds (preformed parts) and roots do not have