The Maryland EnvirothonForestry 2010 Resource SiteThis is an online study guide for advisors and students participating in the Maryland State Envirothon competition. It is not inclusive of all content you may need to know for the state competition. Web sites provided are for reference only and may not be exactly what students are tested on.

Forestry - Measurements

Introduction:

Like many other disciplines, forestry is a science based on measurements. While participating in the Envirothon program, you will learn to use the same instruments and collect the same data that professional foresters use to learn about and manage our forest resources. Many students enjoy the forestry section of Envirothon because it is very “hands on”. Becoming proficient with basic forest measurements is very important, because many of the more complex measurements require accurate forest data collection.

Learning Objectives:At the end of this section, you should:

- Understand why measurements are important in forestry and understand which tools are used to obtain specific measurements.
- Demonstrate proficiency in “pacing” to measure distances and determine how many paces you have in a chain (66 feet or 19.8 meters).
- Demonstrate proficiency in the use of the following forestry tools:
- Diameter Tape

- Biltmore Stick/Merritt Hypsometer

- Clinometer

- Wedge Prism

- Conduct a sample plot as part of a forest inventory using forestry instruments
- Apply data to specific charts and tables to determine forest growth conditions.
Let's Get Started:Determining the number of logs or sticks in a tree

Determining the volume of a tree

Determining the firewood volume of standing trees

Determining the stocking level

Determining stocking level using a table

CHAIN FACTS:

- 80 chains = 1 mile (1.61km)
- 10 square chains = 1 acre (very helpful in determining the size of wildfires!)
- Several forestry tools are calibrated to be accurate at one chain.

- With both eyes open, aim the black crosshair of the clinometer level with the base of the tree at the soil. Using the right-hand scale (the left scale is for measuring percentage of slope) you will read a “negative” number if the tree is on level ground or down slope. You will read a “positive” number if the tree is up slope.
- With both eyes open, aim the black crosshair of the clinometer to the top of the tree. This is a tricky measurement because your view may be obscured by leaves or nearby tree branches. If the top of the tree were an open umbrella, you’d want to be aiming at the point on the top of the umbrella.

- Add or subtract the numbers:

1) If your eye is at a level between the base of the tree and the top, the two numbers are added together to determine total height.

2) If your eye is below the level of the base of the tree (upslope from you), the base reading must be subtracted from the top reading to determine total height:

Determining the number of logs or sticks in a tree:The

Merritt Hypsometerworks much like the clinometer, but it’s much easier to use:

- Standing one chain away from the tree, hold the stick upright 25” (63.5 cm) away from your eye with the
Hypsometerside of the stick facing you.- With the butt of the stick aligned with the base of the tree, count the number of 16-foot logs by matching the graduations on the stick to the trunk of the tree, until you reach an 8” (17.9 cm) top or the first major
defectin the tree. A defect may be a large branch, a bend in the trunk, or a hollow cavity that would cause that part of the tree to be unusable at the sawmill. Measure to the nearest half-log (for example: 1 ½ or 3 ½ logs is OK)- For pulpwood, measure to a 4” (10.1 cm) top, defects are less critical because the tree will be ground up into chips, not sawn into lumber.

Determining the volume of a tree:

A tree's age, when compared to its diameter or height, can be an excellent indicator of how productive a specific

siteis for growing a particular species of tree, or can be an indicator ofstocking(or how crowded the trees are).Because trees are many times older than we are, growth rings serve as a “history book” of the tree and its surrounding community. Droughts, wet seasons, injuries, and even forest fires can be reflected in tree growth rings.

On standing trees, age is determined by using an

, which is a threaded hollow drill that is turned by hand into a tree’s trunk until the borer reaches the center of the tree. Theincrement borerincrement core, a pencil-thin sample of wood, is extracted from the trunk, showing the tree’s growth rings and ring spacing. Although this boring does not usually harm forest trees, it is not recommended for urban or other “specimen” trees. During the Envirothon competition, a sample increment core or the tree’s known age will usually be provided.

Determining the firewood volume of standing trees:To determine the firewood volume of standing trees, foresters use a

.cord volume table

Determining the basal area of an individual tree requires a d-tape and a calculator. The formula is:

BA = .005454 X DIAMETER^{2}SQUAREDForesters use a surprisingly simple, yet innovative instrument to determine the basal area on a specific site or

sample point. Theis a small piece of glass that has been ground to refract light rays at a specific offset angle, which creates an “optical illusion”. Technically speaking, in most eastern forests, we use a 3.03 diopter prism ground to an angle of 104.8 minutes. Most importantly, this means that tree that is measured orwedge prismtalliedis equal to 10 square feet of basal area, so we are using a wedge prism that has abasal area factorof 10 (BAF = 10).When using the wedge prism, it is very important to remember that the instrument must always be held directly above the “plot center” stick for accuracy.

The “optical illusion” the wedge prism creates (as a result of the angle it is ground) appears to “offset” a portion of the tree’s stem or trunk when viewed, preferably at DBH. If the offset portion viewed through the prism appears to connect with the main stem of the tree, you will “tally” that tree as “in” or “countable”. If the offset portion appears completely removed from the main stem of the tree, do not “tally” that tree as it is “out” or “not countable”. For trees that appear to be “borderline” or on the edge, simply tally every other tree. The following diagram illustrates this measurement:

After determining the number of “in” or countable trees, as well as any every other “borderline” tree, simply multiply that number by 10 to determine your basal area (because you are using a 10 BAF prism). For example, if you have 8 “in” trees, your basal area is 80, or you have “80 square feet of basal area per acre”. If you think about it, an acre (.4 hectares) contains 43, 560 square feet, while in this example, only 80 square feet is actually occupied by tree stems, or trunks. The branches and crowns of the trees, as well as other smaller vegetation occupy the remainder of a forested acre.

Determining the stocking level:

Although each measurement is sometimes conducted on the same sample plot, don’t confuseAn important tip:basal areawith the1/20. When using the wedge prism above “plot center”, measure all of the trees as far as you can see (there may be a huge tree in the distance that is “in”). When counting trees in your 1/20^{th}acre tree count^{th}acre plot, count only those within the radius of your circle. During the Envirothon competition, each of these measurements would be conducted on a separate plot to avoid confusion…

Determining stocking level using a table:

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