Before forest landowners can make a decision on what to do with their
forest, they must know what resources their forest has. For this
reason, a forest
inventory must be conducted to obtain the necessary information.
Forest inventories can be complex, depending on how thorough you want to
be and what information you desire. Inventorying 100 percent of your
property may be expensive, and most likely unnecessary, unless you have
extremely high valued timber (i.e. black walnut or black cherry) of
exceptional quality. For this reason, foresters use statistically
proven inventory techniques, of which several exist.
Before statistical models can be applied, field data must be
obtained. Tree species, height, diameter, and age are some of the
data foresters collect. Foresters use an assortment
of tools that assist in collecting data.
Tree Height
How do you measure a tree's height without climbing it?
Through a trigonometric calibrated tool. Two common tools can be used to
determine the height of a tree: the Merritt
hypsometer and the clinometer.
Both of these tools are used at a distance of 66 feet from the tree;
therefore, given that distance the height can be determined by observing
the angle from the top of the tree to the bottom of the tree. The top of the
tree is generally determined by its merchantable timber
value. It is not included if it can not be used for
lumber.
Tree Diameter
There are several tools available that allow foresters to determine
a tree's diameter. One tool, the Biltmore stick, is included in the same measuring
stick as the Merritt
hypsometer. A more accurate tool that is frequently used
by foresters is the D-tape
(diameter tape). This tape is calibrated to measure a tree's
diameter based on its circumference. Almost all tree diameters
are measured at breast height, four and a half feet above ground
level. Due to the unevenness of the ground, ground level is
considered the highest point at the tree's base. These
standard measuring procedures allow foresters to collect
reproducible data.
Tree Age
Besides cutting down a tree, the easiest way to determine a
tree's age is to collect a core sample with an increment
borer and count the growth rings. Each year a tree
produces a ring of wood that adds to its diameter. By taking a
closer look at these rings, foresters can determine the rate trees
are growing, which is useful for establishing timber stand
improvements (TSIs) by removing competing trees to increase tree growth.
Core from a white pine
Tree rings can tell scientist more than just how fast a tree is
growing. As a matter of fact, the study of tree rings is a science in
itself, known as
dendrochronology.
By closely investigating the growth patterns of old trees, dendrochronologists can better understand significant events in archeology
(i.e. when trees were last felled), climatology (i.e. investigating pre-record,
before records were kept, precipitation per year), ecology (i.e. investigating the effects
of air pollution on tree growth), hydrology (i.e. dating when trees were
damaged by floods), and pyrochronology (i.e. dating fire scare to
determine their frequency). Much information that we know
today about pre-record global conditions comes from
researching
tree rings.
