Tree measurement studies

The following six protocols are used to measure specific trees and collectively a forest stand. Each of the protocols are outlined below and data sheets for an overall set of tree measurements are included in the section on forestry field notes.

Measuring Tree Diameter
To measure the diameter of a tree, we measure the distance around the tree (circumference) at chest height (1.35 m), then convert this to the distance through the tree (diameter) by dividing by 3.14.  We have a special tape measure that converts circumference to diameter when we make this measurement.  Record this measure called DBH (Diameter Breast Height) in the table for each tree.  You can make these tapes by marking each 3.14 cm as 1 cm on a heavy plastic tie used in lumber yards.

You can download instructions for making you own DBH tapes by clicking here.

Measuring Tree Height
To measure the height, use the clinometer showing tangents rather than angles. Move 10 meters from the tree.  Site to the top of the tree and record the tan. Convert this into height by multiplying the tan by the distance you are from the tree (10 m). Next, site to the base of the tree and record the tan and repeat the height calculation, add the height to the base if it is downhill from the observer, and subtract the height if it uphill from the observer.  Record the total tree height.  If the tree is too tall, then move to 20 m distance and repeat the process.

Tree Age
We can take a sample through the tree that shows the annual rings of the tree. We use an increment bore to drill a sample from the outside edge to the middle of the tree. We try to take this sample as close to the base of the tree as possible so we do not miss many years of growth. When we drill a core sample, we glue the sample into a block of wood, sand it smooth then count the year of each rings beginning at the outside ring as the year we took the sample. The early season growth shows as a larger, whiter band of cells in the rings of the tree. The later season growth shows as a darker band of smaller cells. As the tree grows a layer of wood around the trunk, it also grows in height. The seasonal rings tell the age of the tree, how well the tree grew in each year and provide a record of the conditions that result in tree growth.  See the web pages on dendrochronology for a more complete description.

Canopy Closure
Run a 100 m transect from a set waypoint at a given azimuth.  You may run parallel transects at wayoints that are offset from the first but along the same azimuth.  Two field workers, one as observer, the other as recorder walk the transect.  The observer uses a handheld densiometer and tells the recorder if there is vegetation (i.e. branches, leaves, needles) at the crosshairs of the densiometer or not. etc.  Take a reading at each meter along the transect (See UK or GLOBE manual).  Determine if canopy cover is open or closed byanalysing results using densiometer data forms.

Forest infestations, forest health