Tree Base Position   Robert Leverett
  Sep 19, 2005 06:12 PDT 
(full article)

    As a final topic, the location of the ideal base point of trees on
sloping ground continues to haunt me. Imagine a plane sloping downward
from south to north at one rate and from west to east at another rate.
Drop a white pine seed and let it grow into a tree of huge proportions.
The tree sloughs off bark and deposits needle material to a depth of 6
inches to nearly a foot in the notches between root flares. Make the
flares of different sizes. The sloping plane of the surrounding ground
indicates the level at which the original seed fell. Observe that extra
organic matter has piled up against the uphill side of the tree and
washed away from the downhill side. Now from this complex structure
decide where the base point is for determining the standard CBH point.
No simple exercise. However, for modeling volume, the tree structure
must be taken all the way down to where the roots disappear into the
ground. We in ENTS are interested in the whole tree above ground level,
not simply the merchantable portion of the trunk above the uneven root
flare. Oh my aching .


Robert T. Leverett
Cofounder, Eastern Native Tree Society
Base of Tree   Edward Frank
  Sep 19, 2005 20:58 PDT 

What defines the base of a tree is a crucial question for our group - where
do we start our height measurements? Conceptually the answer is quite
elegant.   Colby Rucker stated this simply (Aug 11, 2002), " All height
measurements start from the same place - "where the acorn sprouted."   The
application of the principle is where the trouble begins, but I do believe
that any interpretations of the tree base should be true to this concept.
Trees will sprout virtually anywhere and the physical landscape changes over
periods of time. I don't think this single simple definition of the base of
the tree will suffice.

In many cases with trees on level or slightly sloping ground where little
alteration of the ground surface has taken place, the base of the tree can
be determined fairly easily. In cases where trees are on sloping surface
with debris accumulation and soil erosion, where the trees are sprouting
from the side of a rock outcrop, where trees are growing on nurse logs,
where trees are growing in a swamp or marsh, and where trees are growing as
epiphytes on other trees, the determination is more complex.

The core definition I want to use is: The base of the tree is where the
projection of the pith (center) of the tree intersects the EXISTING
supporting surface upon which the tree is growing.

Trees often sprout and begin their life on nurse logs. These logs
eventually decay and the initial sprouting point may be a foot, or in the
case of some of the giant western trees 10's of feet above the existing
ground surface. Over time these exposed tap roots grow bark and become
virtually indistinguishable from other portions of the trunk. This
definition would avoid the necessity to make those distinctions.

In cases where the ground has been eroded to a lower elevation by this
definition any exposed root above the ground surfacedirectly beneath the
center of the tree would be included in the tree height.

Trees growing on the side of a cliff would still have their base at the
cliff side as that position would be the intersection of the pith of the
tree with the supporting growth surface. Roots that extend down the side of
the rock face would not be considered toward the total tree height, just as
exposed roots extending down a hillside are not considered toward tree

Trees growing as epiphytes on other trees would have their base defined as
where their pith intersected the supporting surface, in this case the branch
or trunk, upon which it is growing. [In Olympic National Park, WA this
summer I saw a large red cedar upon which two tree sized western hemlocks
were growing, The largest epiphytic hemlock was likely 50 feet high and a
foot or more in diameter and was perched on a notch of the cedar 20 feet
above the ground - so this is a real-life consideration].

There are trees that grow from spreading roots or from braches that have
touched the ground ad sprouted.   The base of these trees would be the point
at which their new trunk emerges from the supporting surface.

Trees growing in swamps or marshes would have their base measured from the
bottom of the water pool in which they were growing. Some species sprout
from floating seeds, so where the acorn fell is difficult to apply. These
trees should not be measured from the water surface as seasonal changes in
water level or tidal fluctuations would be constantly changing the base of
the tree and tree height. This would provide a stable figure for the base
of the tree and tree height..

There is a compromise in this definition by allowing in select cases what
originally was a root to be counted toward the tree height. However by
accepting this occasional case, a general definition can be made that
overall satisfies more cases than does the basic "acorn sprouts" concept.
There is still the problem of applying the definition in the field, and I
believe that is best addressed on a case by case basis by whomever is
measuring the tree. There may still be cases where the definition can not
be applied, then the person making the measurement should use their best
judgment and note the special condition when the information is reported.

Ed Frank
RE: Base of Tree    Robert Leverett
   Sep 20, 2005 06:25 PDT 


   Excellent summary of the principal points relating to discussions on
how to locate the base of the tree. I'm a little embarrassed to say that
it has taken a long time for me to become serious about figuring out for
myself at what internal, computed point I should fix the base of the
tree as "the spot at which the acorn sprouted".

   The fairly smooth, though tilted, land surface that characterized
the location in the William Cullen Bryant estate at which I was
measuring on Sunday presented me with an unavoidable challenge. I
realized that I needed to fix the base point more accurately for
modeling purposes. The uneven and uplifted spread of roots intersecting
with the generally smooth plane of the ground produced several equally
likely looking spots. Well, this has always been the case, but
heretofore, I've stood back, sighted a line down the trunk at mid-slope,
and went to the point of root intersection with the ground, chose a
point between two root flares and declared it to be the base point for
CBH measurements. Others might have chosen a slightly more liberal or
conservative point.

    In the case of the particular pine I was modeling on Sunday, if I
backed off to the smooth, tilted land surface at mid-slope, I got a
circumference of 13.6 feet at 4.5 feet above that level, as opposed to
as low as 12.4 feet when I took a conservative approach and climbed upon
the root collar. The big pine had created a hummock with its needles and
sloughed off bark. In settling on a base point for CBH measurements, I
didn't actually go to the base of the hummock. I was still a little
conservative - thus the 13.1-foot circumference. A more conservative
measure is 12.3 to 12.5 feet. The trunk tapers quickly.

    One of the unproductive conventions we in ENTS must shed is the
inclination to want to climb above the exposed root collar (at
mid-slope) to identify the "base" of the tree as a point in or at the
top of the root collar, i.e. at the base of what appears to be all
trunk. For volume modeling, what shows above ground level needs to be
included except in the case of obviously lateral roots. The bigger the
tree, the more complex this determination becomes.

     BVP has a methodology for modeling a tree's base. His is probably
the best thought-out process in the universe, but I don't know exactly
how he makes his calculations.