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
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
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
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
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
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.
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
Regular Article Index