I am not debating whether or not the accuracy reflected in the American Forest lists are sufficient for to be useful to the general public, or used to create interest among members of the general public. That is not why I want to compile the list of mismeasured trees and is another argument entirely.   The purpose of the list of mismeasured trees is to demonstrate that in field usage the ENTS techniques provide more accurate and consistent results than do forestry clinometer and tape techniques, and that these laser techniques are not subject to some of the errors outlined in Will Blozan's Tree Measuring Guidelines document. There are many examples of grossly erroneous measurements that have appeared in one publication or another. Will Fell has argued that these grossly inaccurate measurements are a result of improperly applying these basic forestry techniques and with proper usage, better and reasonably accurate measurements can be made. That idea that better measurements could be made is undoubtedly true, but I still do not believe the numbers generated would be sufficiently accurate for rigorous scientific applications. The counter argument is by using numbers that have been published in these champion lists, numbers are being used that have been vetted to some degree and represent a fair sampling of measurements taken with reasonable care by responsible individuals using those techniques.  

Ed Frank

ENTS:

I would like to highlight some of the problems with the traditional baseline methods.  I see four specific examples I want to discuss, there may be others: 1) The measurement may not be taken from a great enough distance to see the actual top of the tree, 2) The top can be seen but from the ground it determining which sprig forms the top is difficult using conventional baseline/clinometer methods. With a laser rangefinder the distance to the sprigs can be determined in real time where the most distant of several branches at similar angles represents the highest sprig. 3) The top measured using baseline methods may unknowingly be a branch extending outward toward the viewer rather than being the true top. This will result in the height being significantly over-estimated. By using a laser rangefinder these frontward extending branches can be distinguished easily. 4) The top of the tree may offset and not located exactly over the base of the tree. 

In a sampling of 1800 trees measured using the laser techniques found the tops of trees in the set to be offset an average distance of 13 feet from the top representing an average offset along the line of sight of 8.3 feet. In a 150 foot tall tree measured from a distance of 100 feet this average offset would lead to an average height error of 12.5 feet based on this average offset alone.  The actual top may be behind or in front of the base of the trunk along the line it is being measure.  If the top is located behind the trunk (farther from the observer) then the resulting height calculation would be low. If the top is offset toward the observer, then the resulting height calculation will be erroneously high. 

To elaborate half of the errors from the top of the tree being offset from the base would be greater than the average offset errors (and half the errors would be less than the average offset errors).   I think that the tops measured are more likely to be on the facing side of the tree than on the opposite side of the tree, but for calculation purposes we used to calculate actual offset, this front to back asymmetry is not important. [It could be calculated from the dataset]. Therefore the likelihood of a tree being measured resulting in a value that is too high, even if the actual top is found would be greater than the chance of it being underestimated. If the measurer is not hitting the top, then the result would be high in virtually every case. The laser lets you identify the top more clearly than other methods because it generates a distance number as the tree is being scanned.  The chance of not picking the correct top is much much greater when just guessing using baseline/clinometer methods than they are when using a laser. Most of the larger errors are the result of misidentifying the top, lesser errors are a direct result of the top not being directly over the base, even if it is identified correctly.

I have been encouraging Bob to use some trees that have been climbed and physically measured in his height measurement experimental designs.  I also have been lobbying Will and Bob to prepare a list of trees which have been climbed and measured by drop tape for which we also have laser/clinometer height measurements.

The point is that many people need to have the reassurance that all of the triangulation methods are actually somewhere close to right, and are meaningful. A taped measurement, even if older addresses that concern and adds weight to the entire argument. If you demonstrate that a taped measurement is close, or was close in height to the instrument and trigonometric calculations, then people will believe the instruments and trigonometric numbers are meaningful. 

Many people are so involved in using electronic, mechanical, and mathematical measurements and modeling, there is a degree of disjunction from members of the general public.  Most people do not regularly use nor fully understand math beyond addition and subtraction, and distrust science even more. How many advertisements do you see where people almost seem proud of their inability to use a computer? Trees that have been climbed and measured need to be included in any comparison of tree height measurements, no matter what the intended audience. 

Edward Frank