Measurement Ideas that Made a Difference

Kim Iles, Inventory Consultant

There have only been a few big ones.  They changed the way the business was done – not forever, but at least until the next big idea changes everything again.   

Sampling and Regressions

F.X. Schumacher, the Duke professor led the charge.  He introduced the ideas of sampling to Federal agencies, private companies and generations of students.  Statistics introduced the idea of sampling error (a mixed blessing).  Regressions made tables more reliable and extended them to many dimensions.  Computer models are one of the eventual extensions of that regression idea.  

Variable Plot sampling

Sampling with variable probabilities had been used before, but this method was a lot more than that.  It was a clever trick with tree geometry, and it was made practical by a simple angle gauge.  It blew the socks off fixed plot sampling, which is now relegated to infrequent use and special purposes.  Walter Bitterlich in Austria developed the Variable Plot method for obtaining basal area and invented the Relascope to do the work.  Lew Grosenbaugh extended the method to measuring everything else (volume, number of trees, etc.). 

Count & Measure plots

This made a major difference in efficiency to a system that was already a wild success.  In the Pacific Northwest, Don Bruce (co-author with Schumacher on a forest measurement text) had this insight, and his son, Dave Bruce, introduced the wedge prism.  

3P Sampling

For years, we had sampled to find out what was there.  Suddenly, we were sampling to adjust an existing estimate.  This was already an important trend in statistics, but the mechanics of how to choose the measured trees in the field made all the difference in forestry.  This development by Lew Grosenbaugh of the USFS is the only forest sampling method on a par with Variable Plot Sampling.  


Matching up a large database with a physical map was a big step.  Geographic Information Systems have begun (at long last) to work reliably and practically.  They are eliminating strata, and keeping information on individual forest polygons.  Global Positioning Systems, which link all kinds of data to those forest polygons, are coordinating information in ways that forestry has never seen.  When computers stopped printing numbers and started displaying information, the world changed. 

Taper Equations

This got us away from simple volume descriptions that were limited to volume.  It put attention in the right place.  We were attempting to describe an item (a tree stem) in many ways – not just one answer in one unit.  All of a sudden we were asking the question “Exactly what is the product here? 


The instruments in forestry have not become more clever.  They have, however, become more useful.  They are smaller, lighter, and oil dampened.  Lasers, to measure distance directly, are certainly increasing speed.  Eventually, a temporary photo scanned by a computer chip might take us toward measuring the entire stem, and perhaps storing that data.  Automatically recording the information has been only partially useful, but putting the numbers into data recorders has been a success.  If we can remotely sense the big changes in plots (like dead trees and cut trees) we will need to visit them far less frequently, and only to check the actual growth against a growth model estimate.   

Smaller Possibilities for the Future 

Critical Height Sampling

There is a good chance that using Variable Plots, by measuring the change in Critical Height will replace fixed plots in growth and yield studies (at least for the growth part of the determination).  Mortality can be checked on large fixed plots, but all that needs to be done is to measure the trees when they die – not every time.   

“Surface” GIS systems

Right now, an entire polygon normally has the same volume/acre.  In the future, it is easy to imagine a “surface” across the polygon that shows the volume varying from one side of the polygon to the other.  We already do this for elevation, why not for volume, value, species mix and so on?  This can be partially automated with scanners.  Artificial sudden changes in our description of the land base will eventually disappear.  Stereo maps are an obvious step, and comparing them to new stereo photos will be an excellent quality control method. 

Originally published April 2001

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