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 ……. Bob Robert T. Leverett Cofounder, Eastern Native Tree Society Base of Tree   Edward Frank   Sep 19, 2005 20:58 PDT  ENTS, 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 height. 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  Ed:    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. Bob      Home