Attachment 4 - QualifiedCruiserReferenceGuideRevised04282013.doc

QUALIFIED CRUISER REFERENCE GUIDE

Prepared by Approved by Michael Van Dyck Paul Momper Regional Measurement Specialist Director of Renewable Resources Modified by: RJost, RMS 4/28/13 Foreword

This document was developed as a reference manual for use in the training and certification of qualified cruisers for the Eastern Region of the USDA Forest Service as specified in the Timber Cruising Handbook (FSH 2409-12, Chapter 60). This is one part of a suite of tools that were developed for this purpose.

In order to be certified as a qualified cruiser, a passing score is required on both a regionally approved written test and a regionally approved field test.

1. ROLE OF THE TIMBER CRUISER

The role of a timber cruiser is an extremely important one. Timber cruisers collect field data used for the determination of timber product volumes and values. This information is used in the preparation of timber sales.

The timber product volumes and values determined by cruising are even more important in Region 9 than in western regions. In Region 9 payment for the majority of timber sales is based directly on the cruised volume. There is no additional measurement of the harvested products to determine final payment.

Cruisers usually work as part of a marking crew or cruising crew, but each individual is responsible for their own precise and accurate measurements. The reliability of the cruise will depend on the skill of each individual cruiser. Good observation skills and good judgment must be used at all times.

Timber cruising is more than just taking measurements. There is a great deal of skill involved in recognizing the form, soundness, and overall condition of the trees. In many cases the cruiser has the final decision as to which trees will be harvested and which will be left to grow and reproduce.

1.1 – Cruiser Certification Levels

There are four levels of certification for cruisers. They are described below in order of increasing responsibility. Each higher level of certification includes all of the responsibilities of the lower levels. These responsibilities, as well as many of the other things discussed in this document, are discussed in the Timber Cruising Handbook. This is also known as the Forest Service Handbook 2409-12. Every district is required to keep printed copies of the Forest Service Handbooks.

1.1.1 – Qualified Cruiser A qualified cruiser is responsible for applying correct volume determination techniques while working alone, as a crew member, or as a crew leader. The required knowledge and training are described below.

1.

Proficiency in timber cruising fundamentals, including as a minimum:

a.

Tree measurement (diameters and heights).

b.

Species identification.

c.

Defect recognition and determination.

d.

Quality determination.

e.

Use of timber cruising tools.

f.

Map reading and compass use.

g.

Traverses.

h.

Elementary use of aerial photography.

2.

A working knowledge of the cruise systems used in the region.

3.

Demonstrated ability to interpret and follow the timber cruise plan and cruise data recording instructions.

4.

Passing scores on both a regionally approved written test and a regionally approved field test, conducted on prepared certification test areas. Topics tested will include species, measurements, defects, and other information representative of what the cruiser normally encounters.

1.1.2 – Advanced Cruiser An advanced cruiser has all of the responsibilities of a qualified cruiser, and in addition must be able to train prospective qualified cruisers and design cruises. Experience, technical aptitude, and ability to train others are required. Training is required, and a regionally approved written test must be passed.

1.1.3 – Check Cruiser A check cruiser is responsible for check cruising individual cruiser performance and each timber sale, providing cruiser training for qualified and check cruisers, a check cruiser also maintains records of cruiser certifications. The forest field test course for certification of qualified cruisers is established and maintained by a check cruiser.

1.2 – Maintenance of Certification

As long as a cruiser’s performance continues at a satisfactory level the certification is indefinite. This is true for all levels of cruisers. The following criteria must also be considered.

1.

If a cruiser has been inactive for a period of more than one year, refresher training is required prior to resuming cruising.

2.

All levels of cruisers, whether active or inactive, must attend formal training or workshops intended to update their skills at least once every four years to maintain knowledge appropriate to the level of certification.

3.

Check cruisers may recommend loss of a cruiser’s certification based on unsatisfactory performance.

2. SPECIES IDENTIFICATION

A timber cruiser must be able to correctly identify all of the species that will be encountered, in all of the seasons of the year. This is a learned skill, and may take time and practice to master. Cruisers learn to identify species by foliage, bark, buds, branching patterns, overall shape, cones or seeds, and other characteristics.

Merchantability specifications and product value depend on correct identification of species. The volume equations used to calculate the product volumes produce different volumes for different species due to variations in the tree forms between the species.

Region 9 is a very diverse region in terms of the number of commercial tree species. Table 2 contains a list of all of the commercial species currently recognized in the region for the purposes of cruising. There are over 100 species listed. Notice that in addition to the scientific name and “official” common name there is a unique numeric code used to identify each species. Cruisers must know the numeric codes for species common to their area since all of the software used to process the cruise data requires these numeric codes.

Table 2 – List of commercial tree species for the Eastern Region of the USDA Forest Service.

Some of the listings in table 01 are for an entire genus. These have only the genus name in the column for scientific name, and have the designation “Spp.” in the common name. These codes are for use with species of that genus that are not one of the particular species listed. These codes may also be used when cruisers are instructed not to differentiate between species of a particular genus.

3. PRODUCT DETERMINATION

After trees are harvested, they are usually made into some sort of product that people use. Some common products are boards, veneer for plywood, power poles, fence posts, house logs, railroad ties, mining timbers, chips, pulp, firewood, and more. Different parts of the same tree may be converted into different products.

There are several different product categories into which trees, or parts of trees, can be placed. Table 3 lists the products most commonly used in Region 9, along with the numeric code for each. Not all of the products mentioned above have codes. Cruisers will need to become familiar with the products and codes used on their forest.

Table 3 – Products and Codes

*Code 08 is used only if dead material will be sold at a different price than live material.

Every tree will be assigned a primary product code. This represents the main product category into which the tree has been placed. The assignment of a primary product code is usually based on things like species, diameter, length, and quality of the wood in the tree. It is important to note here that the tree may not necessarily be made into the product assigned by the cruiser. In fact, many products don’t even have codes. The product codes are assigned so we have an estimate of the amount of volume that can be expected to meet different sets of criteria. In a timber sale contract, the different products typically have different prices bid for them. Once purchased, the trees can be made into any product the purchaser wants to make.

If a tree is assigned a primary product code for sawtimber (01), a secondary product may also be assigned. Sawtimber usually does not represent the entire usable amount of tree stem. There are quality and diameter standards for sawtimber. Parts of the tree stem not meeting these standards are not considered sawtimber. The usable part of sawtimber trees above the sawtimber part is called topwood. Cruisers will need to become familiar with the topwood products that are used on their forest. If topwood is not to be harvested, it might not be recorded at all.

All products have specifications associated with them. There is usually a minimum diameter that must be met, and there may be quality specifications as well. The specifications may vary by species. In addition, some species may be prevented from having a particular product code. For example, on a particular cruise it may be specified that aspen will not be coded as sawtimber regardless of tree size. These specifications will be identified in the “Cruise Plan” specific to each timber sale and must be read and understood by the cruiser prior to collecting sample tree measurements and/or tree count information.

4. DIAMETER MEASUREMENT TOOLS

One of the most important measurements made in a timber cruise is tree bole diameter. Bole diameter is a main determinant of the volume calculated for a tree. It may also determine which product category the tree falls into.

The goal of a timber cruise is usually to determine the volume of wood in the stem of the trees (inside the bark). It might seem logical, then, to measure the diameter inside the bark (DIB). This is not practical in the field, however, so stem diameters are almost always measured as diameter outside bark (DOB). Bark thickness is taken into account in the computer programs that calculate the volume of the wood.

Tree bole diameters are nearly always measured using one of two tools: a steel tape or tree calipers. Use of these two tools will be discussed separately below.

4.1 – Steel Diameter Tape A steel diameter tape is the most common tool used to measure tree bole diameters. The tape is wrapped tightly around the tree stem perpendicular to the axis of the stem at that point. Care must be taken to get the tape straight around the tree, with no twists and no objects between the tape and the bark.

Small protrusions of surface bark sticking abnormally high above the regular surface of the rest of the bark should be removed so the tape rests tightly against the remaining bark. Examples of this might be a curl of bark on a birch, or loose bark protrusions at a seam. Any more substantial protrusion would be considered a stem abnormality, and would be handled as described in a later section devoted to measuring diameters when abnormalities are present.

A diameter tape is graduated to read the diameter directly, with no additional calculations necessary. It relies on the mathematical relationship between circumference (the distance around) and diameter, assuming the tree bole is circular in cross-section. The scale graduated for diameter measurements is usually on the reverse side of a tape reading in standard measurements. For example, a loggers tape may read in inches on one side and in diameter-equivalent-inches on the other.

A diameter tape is quite accurate and fairly easy to read if used correctly. There are four basic types of diameter tapes, differing only in whether the tape case is typically held in the right hand or left hand when passing the tape around the tree, and in whether the graduations are on the top or bottom of the tape (figure 4.1b).

Figure 4.1b – The four types of diameter tapes

All diameter tapes have an index mark, usually labeled with a zero, which is used to read the diameter. The end of the tape with the index mark should be wrapped either above or below the other part of the tape so the index mark touches the graduated edge of the other part of the tape (figure 4.1b). The tape must be held so the index mark and the graduations where the diameter is to be read are both tight against the tree. This means the tape makes contact with the tree for slightly more than a full rotation around the tree (figure 4.1c). Note in the “incorrect” image in figure 4.1c how the tape is lifted off the tree where the tape crosses itself. This will result in a diameter reading that is too large.

Figure 4.1c – Wrapping a diameter tape

On diameter tapes with English units the graduations are one-tenth inch. If the index mark falls exactly on a tenth-inch mark the diameter is read directly. If the index mark falls between tenth-inch marks, always round down to the next lower tenth-inch. This is done because trees tend not to be perfectly round, so the diameter is slightly overestimated using a tape.

Figure 4.1d shows three diameter tape measurements. All three of the diameters should be read as 9.3 inches. The third example reads nearly 9.4 inches, but the diameter is always rounded down.

Figure 4.1d – Example diameter tape readings

4.2 – Tree Calipers Tree calipers are made up of three main parts: a graduated main beam, a fixed arm at the end of the main beam, and a sliding arm. The calipers are held perpendicular to the axis of the tree and the arms are closed so they touch the bark on both sides of the tree. The diameter is read from the scale at the inside of the sliding arm, rounded to the nearest tenth-inch (not always rounded down).

Figure 4.2a shows a tree caliper being used on a tree stem (shown in cross-section). The close-up in the inset shows a diameter reading that would round up to 12.7 inches.

Figure 4.2a – Tree caliper

Because trees tend to not be perfectly round, two measurements should be taken and the average of the two measurements should be recorded. The two measurements should be made perpendicular to each other whenever possible. Figure 4.2b shows two perpendicular measurements on the same tree.

Figure 4.2b – Perpendicular diameter measurements using tree calipers

5. DIAMETER AT BREAST HEIGHT

In order for bole diameters to be meaningful, they have to be measured in a consistent way for all trees. A nearly universally accepted method measures diameter at breast height, or DBH. This is a measurement made outside the bark, perpendicular to the axis (or centerline) of the tree, at a height of 4.5 feet above the forest floor on the high-ground side of the tree (figure 5).

Figure 5 – Normal location of DBH Some conditions and abnormalities require DBH to be measured at a different location on the bole. These are discussed individually later.

5.1 – Sloping Ground This is not really a special condition since the procedure is exactly as described, but it is included here for clarity. DBH is measured perpendicular to the axis of the tree at a height of 4.5 feet above the high-ground side (figure 5.1).

Figure 5.1 – Location of DBH on sloping ground

5.2 – Leaning Tree DBH is measured on a leaning tree just like a tree on sloping ground, as if everything has been rotated so the ground is horizontal. The distance of 4.5 feet is measured parallel to the axis of the tree, and DBH is measured perpendicular to the axis of the tree (figure 5.2). Notice that figure 5.2 is just figure 5.1 rotated so the ground is horizontal.

Figure 5.2 – Location of DBH on a leaning tree

5.3 – Forked Tree A tree is said to fork when the bole divides into two or more main stems. The fork is considered to begin at the point where daylight can be seen between the two stems.

When a tree forks below 4.5 feet it is considered two trees. The diameter of each stem is measured at 4.5 feet above the high-ground side (figure 5.3, tree A).

When a tree forks at or above 4.5 feet it is considered a single tree, and DBH is measured at the smallest diameter at or below 4.5 feet. Tree B in figure 5.3 shows an example where DBH is measured below 4.5 feet because the diameter is smallest below the swelling near the fork.

Figure 5.3 – Location of DBH on forked trees

If the fork occurs very near a height of 4.5 feet, leaf litter and loose bark should be removed to see where the fork actually begins.

5.4 – Tree Growing on an Object When a tree is growing on top of an object, or when the roots are exposed, the forest floor is no longer where it was when the tree began to grow. DBH is measured 4.5 feet above the root crown instead of 4.5 feet above the forest floor (figure 5.4). The root crown is the top part of where the roots all come together. It can be thought of as imagining where the forest floor would be if it were raised up to cover the exposed roots.

Figure 5.4 – Location of DBH above root crown

If roots are exposed on only one side of the tree, the forest floor on the other side may still be in its original position. In this case, measure 4.5 feet above the forest floor. If the forest floor is obviously lower than normal, the root crown should be used as described above.

5.5 – Abnormalities at 4.5 Feet There are a variety of situations that make it difficult or impossible to get an accurate DBH reading at a height of 4.5 feet. Special procedures are designed to deal with these situations in a consistent manner.

Tree calipers can be used to measure DBH for trees with any abnormality at 4.5 feet, as long as the abnormality is confined to less than half the circumference of the tree at that point. Measurements are be made in a direction that results in a diameter unaffected by the abnormality. If the abnormality is large enough to prevent a second measurement with the tree calipers, a single caliper measurement is used.

A diameter tape is generally not stretched across an abnormality because a diameter will result that is not representative of the tree at that point. Other methods of measurement are used in most cases where an abnormality occurs at 4.5 feet.

5.5.1 – Small Catface If the abnormality is a fairly small catface, a tape may be wrapped so that it is extended out to the normally rounded shape the tree would have had without the catface (figure 5.5.1). The tape should not be stretched tight across the catface or the resulting diameter will be too small.

Figure 5.5.1 – Measuring DBH across a catface with a diameter tape

5.5.2 – Short Abnormality If the abnormality is confined to a small enough area that a representative diameter can be measured above and below the abnormality, then use an averaging method. Take two diameter measurements spaced equally above and below 4.5 feet and average the two measurements. Figure 5.5.2 shows three situations where an abnormality (limb, catface, and burl) prevents measurement of DBH at 4.5 feet. A measurement is taken a distance A above 4.5 feet, and a measurement is taken a distance A below 4.5 feet. These two measurements are averaged for DBH.

Figure 5.5.2 – Measurement of DBH using the averaging method

5.5.3 – Long Abnormality If the abnormality is long enough that measurements can not be made above and below it, or if it extends down far enough that it enters the swelling near the stump, then use what is called the half-tree diameter method. Mark two points opposite each other on the stem, and to the sides of the abnormality. With a diameter tape, measure the distance between the marks on the side away from the abnormality (distance A in figure 5.5.3) and then double the measurement.

Figure 5.5.3 – Measurement of DBH using the half-tree diameter method

5.5.4 – Trees Grown Together Two separate trees that have grown together over time are always considered separate trees, and a DBH must be measured for each. If there is no way to get a tape between them at 4.5 feet, the half-tree diameter method described above is used for each of the trees (figure 5.5.4). Tree calipers could also be used on each of the trees.

Figure 5.5.4 – Measurement of DBH on two trees that have grown together

Two trees that have grown together are never considered a single forked tree, even if the first daylight is above 4.5 feet high. This is because the bark that formed before the trees grew together will form a permanent divider, and the wood will always be separated at that point.

5.6 – Down Tree DBH is measured on a down tree in the same place it would have been measured if the tree were still standing. Find the point that would have been 4.5 feet above the high ground side of the original groundline and measure perpendicular to the axis of the tree (figure 5.6). Measure normally with a diameter tape or tree calipers. If the tree is tight to the ground it may be necessary to dig under the tree to pass a tape around. If there is an abnormality where DBH would normally be measured, it is measured as described in a section 5.5.

Figure 5.6 – Location of DBH on a down tree

Soil and duff material often falls off the roots of a down tree and covers the base of the tree. This material may need to be removed in order to determine the location of the original ground line on the tree.

5.7 – Broken tree DBH on a broken tree is measured at the point that was 4.5 feet above the high ground side when the tree was still standing vertically. If DBH is to be measured below the breakage (labeled A in figure 5.7) measure it normally.

Figure 5.7 – Location of DBH on a broken tree

If DBH must be measured above the breakage (labeled C in figure 5.7) a point must be found where the tree was continuous before the breakage occurred (labeled X in figure 5.7). The height is measured up the stump to that point, and then continued from the matching point above the break until a total of 4.5 feet is measured. For example, if the height to point X is 2 feet, then 2.5 feet is measured above the matching point X on the upper part. If the tree is tight to the ground it may be necessary to dig under the tree to pass a tape around.

If DBH must be measured within the area of breakage (labeled B in figure 5.7) it is measured using either the averaging method or the half-tree diameter method as described in section 5.5. If at least half the circumference remains intact at 4.5 feet (on either piece) tree calipers can be used as well.

5.8 – Felled tree DBH is measured on a felled tree in the same place it would have been measured if the tree were still standing. Find the point that would have been 4.5 feet above the high ground side and measure the diameter perpendicular to the axis of the stem at that point. A point must be found where the tree was continuous before the breakage occurred (labeled X in figure 5.8). The height is measured up the stump from the high ground side to that point (labeled A in figure 5.8), and then continued on the severed stem above that point (labeled B in figure 5.8) until a total of 4.5 feet is measured. For example, if the height to point X is 1 foot, then 3.5 feet is measured above the matching point X on the severed stem. If the tree is tight to the ground it may be necessary to dig under the tree to pass a tape around. If there is an abnormality where DBH would normally be measured, it is measured as described in a section 5.5.

Figure 5.8 – Location of DBH on a felled tree

6. HEIGHT MEASUREMENT TOOLS

There are many tools used to measure heights. A tape or graduated pole could be extended up along the stem of the tree and the height measured directly. In most cases this is not practical for cruising applications. Most of the instruments used to measure tree heights while cruising timber are known as inclinometers, because they are used to measure inclines or angles. They require the user to stand some distance from the tree and measure angles to the top and bottom of the tree. All such methods use rules of geometry to calculate tree heights.

6.1 – Geometry

There are three pieces of information needed to calculate a height. These are shown in figure 6.1a, where A is the horizontal distance from the tree, B is the angle to the bottom of the tree, and C is the angle to the reference point on the tree where height is to be measured.

Figure 6.1a – Tree height geometry Two triangles are formed, with the tree making the right side for both. Knowing A and B allows for calculation of X, the height from the bottom of the tree to eye level. Knowing A and C allows for calculation of Y, the height from eye level to the reference point where height is to be measured. The tree height equals X + Y.

Angle B has a negative sign (for example, -5%) and angle C has a positive sign (for example, +85%). When the angles have opposite signs the corresponding heights are always added together, as shown above.

If a tree is not on level ground it is usually most accurate to measure tree height from a point either uphill from the tree or on the same contour as the tree. Avoid measuring from the downhill side of the tree whenever possible.

If, for some reason, the height must be measured from downhill, below the base of the tree, the geometry changes slightly, as shown in figure 6.1b.

Figure 6.1b – Tree height geometry when below the tree

In this case the two triangles that are formed actually overlap. Knowing A and B allows for calculation of X, the height from eye level to the bottom of the tree. Knowing A and C allows for calculation of Y, the height from eye level to the reference point where height is to be measured. Note that Y is greater than the height being measured. In this case, the tree height equals Y - X.

Angle B has a positive sign (for example, +5%) and angle C has a positive sign (for example, +85%). When the angles have the same sign the smaller height is always subtracted from the larger, as shown above.

6.2 – Slope Correction

It is important to note that the distance from the tree is always measured as a horizontal distance. Some electronic devices have built-in systems to correct for slope. A tape, however, has no built-in correction system. A slope correction factor is used to convert a horizontal distance to a distance that can be measured along a slope. Any slope of 10 percent (5 degrees) or greater requires a slope correction. Slope correction is described in detail in section 7.1.

6.3 – Mechanical Instruments There are several mechanical instruments commonly used to measure heights. Some examples are clinometers, altimeters, and relaskops. All such devices require the user to be a specified horizontal distance from the tree. They all measure angles, and use the geometry discussed earlier to calculate heights.

When used for height measurements, these instruments use one of two different scales (or variations of these two). The first is called the topographic scale, which is graduated for direct height readings when the user is a horizontal distance of 66 feet from the tree. The second is the percent scale, which is graduated for direct height readings when the user is a horizontal distance of 100 feet from the tree. The percent scale can actually be used from any horizontal distance. Simply multiply the percent reading by the horizontal distance to get the height represented. An example of this is shown below.

6.3.1 – Clinometer A clinometer is an instrument that displays the angle of inclination at which the instrument is being held. The most common models have an internal scale and are held up to the eye so a crosshair in the display appears to be at the level of the target where a height measurement is needed. Figure 6.3.1a shows a popular clinometer design.

Figure 6.3.1a – Clinometer

The display is not a see-through type, so either both eyes are kept open to line up the crosshair, or one eye is used so that both the crosshair and the target are visible. The display must be read while the crosshair is on the target. Each clinometer has a display with two of the following three scales: degrees, percent, and topographic.

Figure 6.3.1b shows two readings from a clinometer where the left half of the scale is a degree scale (used primarily for slope measurements) and the right half of the scale is a topographic scale (used for height measurements). The angle is read where the crosshair crosses the scale. Values are rounded to the nearest whole number.

Figure 6.3.1b – Clinometer readings, topographic scale

Using the topographic scale, the bottom measurement is -2 (the bottom of the tree is below the user’s eye level, so the sign is negative) and the top measurement is about 21 (the top is above the user’s eye level, so the sign is positive). Since the signs of the angles are opposite, the corresponding heights will be added. At a horizontal distance of 66 feet the topographic scale reads directly in feet, so the tree would have a height of 23 feet (2 feet from the bottom to eye level + 21 feet from eye level to the top).

Figure 6.3.1c shows two readings from a clinometer where the right half of the scale is a percent scale. The reading for the bottom measurement is -3% and the reading for the top measurement is +33%. Since the signs of the angles are opposite, the corresponding heights will be added.

Figure 6.3.1c – Clinometer readings, percent scale If the readings in figure 6.3.1c were read while standing a horizontal distance of 100 feet from the tree, the percent scale would convert directly to height in feet. It would be 3 feet from the bottom of the tree to eye level, and it would be 33 feet from eye level to the top. The height is therefore 36 feet (3 feet + 33 feet).

If the user is standing a horizontal distance other than 100 feet from the tree, the percent scale value (used as its decimal equivalent) must be multiplied by the horizontal distance to get height. For example, if the readings in figure 6.3.1c were read with the user standing a horizontal distance of 75 feet from the tree, the height would be 27 feet (0.36 * 75 feet).

The clinometer is unique among height measuring instruments in that it can be used for certain measurements without looking through the eyepiece. For example, tree lean can be measured by lining up the straight side of the instrument with the stem of the tree, and then reading the angle directly from the visible wheel. This is discussed in greater detail in the sections describing measurement of tree lean.

6.3.2 – Relaskop A relaskop is an instrument that is designed to measure heights in addition to other things. For now we’ll focus only on the height measurement capabilities. Figure 6.3.2a shows a relaskop.

Figure 6.3.2a – Relaskop

Heights are measured with a relaskop in a manner very similar to that used with a clinometer. There are two key differences. First, the display on a relaskop is a see-through type, so the target is always seen with the same eye as is looking at the scale. Second, the scale is read at the top of the visible portion of the scale instead of at a crosshair.

Figure 6.3.2b shows the left half of a relaskop display with measurements for the tree bottom and top. The scale (American style) always has the percent scale on the left and the degree scale on the right. The top half of the display is see-through and is used to sight the target. The target is placed right at the intersection of the see-through section and the top of the scale. The scale is read at the top of the visible portion.

Figure 6.3.2b – Relaskop readings, height scale

The bottom measurement in figure 6.3.2b is -4% (the negative side of the scale is showing) and the top measurement is about 71%. The height would be calculated exactly the same as done with the percent scale for a clinometer, as described earlier.

If a height is to be measured to a point other than the tip of the tree, the relaskop is useful in determining the diameter of an upper portion of the tree stem. The right part of the display has a series of equal-width black and white bars, each of which represents a particular diameter at a particular horizontal distance from the tree. Figure 6.3.2c shows the point on a tree where the upper stem diameter is 4 inches in diameter. At a horizontal distance of 66 feet from the tree, each of the equal-width bars represents 4 inches.

Figure 6.3.2c – Relaskop used to determine upper stem diameter

6.3.3 – Altimeter Altimeters used for cruising are not designed to measure altitudes. They are designed to measure tree heights in a manner similar to that used with clinometers and relaskops.

Altimeters typically have a see-through sight used to point at the target where a height reading is to be taken. The scale, however, is typically not visible in the sight. Instead, the scale is on the side of the instrument. While pointing at the target in the sight, a button is pressed locking the scale in place. The instrument is then lowered and the scale read. Figure 6.3.3a shows one type of altimeter. Note the scale visible along the side of the instrument.

Figure 6.3.3a – Altimeter

There are several scales in most altimeters. They typically have a percent scale in addition to several scales graduated for use at specific horizontal distances. In some models all of the scales are visible at the same time, and in other models only the selected scale is visible. Regardless of the configuration, the desired scale is read where the needle has been locked in place.

The percent scale is used exactly like described with the clinometer. The other scales display heights directly in feet when used at the specified horizontal distance. Figure 6.3.3b shows two readings from an altimeter where the percent scale is being used.

Figure 6.3.3b – Altimeter readings, percent scale

The bottom measurement is about -7%, and the top measurement is about +55%. Height calculations are done in the same way described earlier for the clinometer. If the user is standing a horizontal distance of 50 feet from the tree, the tree height would be 31 feet (0.62 * 50 feet).

6.4 – Electronic Instruments

There are two main types of electronic instruments that are commonly used to measure tree heights: laser-based instruments and ultrasonic instruments. The same geometric concepts discussed earlier are used for height calculation. The main difference is the instrument usually does all of the calculations internally and displays the height directly. Instead of using a tape, the horizontal distance from the tree is measured either with the laser or through an ultrasonic transmitter. An internal inclinometer records the angles to the bottom and top of the tree, and the height is calculated.

Laser-based instruments typically do a good job determining the horizontal distance to the tree if the bole of the tree can be hit with the laser with no interference from branches or foliage. Problems may be encountered in heavy underbrush. Most laser-based instruments have a “three point” system for determining heights. The first point is for horizontal distance only, and can be shot anywhere there is a clear shot to the bole (as long as the tree is primarily vertical). The other two shots are for the bottom and top of the tree. Those don’t need a clear shot to the tree since the internal inclinometer is used instead of the laser.

Ultrasonic instruments work well in heavy underbrush since they don’t need a clear view of the tree in order to get the horizontal distance. An ultrasonic transmitter is hung on the tree, and the instrument picks up the signal and can determine the distance. The transmitter must be at least partially visible, however, so the instrument can determine the angle to the transmitter, and then calculate the correct horizontal distance. The internal inclinometer records the angles to the bottom and top of the tree. Those don’t need to be clear shots either.

7. TREE HEIGHT MEASUREMENT

Tree heights are measured in feet from ground level (not from an assumed stump height). In Region 9, measuring tree height can be more complicated than measuring the distance from the ground to the tip of the tree. Some heights are measured to the tops of certain products within the tree. This type of height is known as merchantable height. An example might be measurement of height to the top of the sawtimber product.

Merchantable height is defined as the height to a point on the stem where merchantability is limited by size, excessive branching, defect, deformity, or log grade. The specifications for merchantable height may vary depending on product. For example, sawtimber products may have different top diameters than pulpwood products.

There are three types of height typically measured. The first is the sawtimber height. This is the height to the top of the sawtimber portion of a tree. Only those trees containing a sawtimber product will have a sawtimber height recorded. The sawtimber portion stops at the highest point where sawtimber product can be cut. The limiting factor can be stem diameter, but it is often something else like branching or defect.

The second type of height is measured to the point above which the main stem drops below 4 inches in diameter. This height is known by several common names, but it will be referred to here as 4-inch height. The third type of height is known as total height, and is measured to the very tip of the tree. Total height should be measured only for species with a well-defined tip. Usually either 4-inch height or total height is recorded for a tree, but not both.

Total height and 4-inch height will be referred to collectively as upper stem heights. Upper stem height is a very important measurement because it determines the overall taper for the tree, which is used in the calculation of the volumes. Because it determines the tree taper, an upper stem height is determined by stem diameter alone. If the top part is not merchantable, it is removed as defect. (Defect calculations are discussed in a later section.)

The rules for measuring upper stem height are different than for measuring sawtimber height. Sawtimber height is usually recorded only to the point where the sawtimber product stops, even if the stem is still larger than the minimum diameter. In this way any upper portion not meeting sawtimber specifications does not need to be dealt with using defect calculations. However, if sawtimber height is the only height recorded for a tree, then the sawtimber height will be used to determine the taper of the tree, so it must be recorded to a known stem diameter. In this situation the sawtimber height is recorded to the specified minimum sawtimber diameter (most typically 9.6 inches for hardwoods and 7.6 inches for conifers) and any non-sawtimber portion is accounted for using defect.

Sawtimber trees usually have two heights recorded: the sawtimber height and an upper stem height. The upper stem height should always be at least as large as the sawtimber height. Special situations are discussed later.

7.1 – Slope Correction All of the height measurement tools used in timber cruising require an accurate measure of the horizontal distance from the instrument to the tree. On relatively level ground this can simply be measured with a tape or any other distance measuring device. On sloping ground, however, the measured distance along the slope can be significantly different than the horizontal distance. Figure 7.1 illustrates this. The measured distance along the slope (C) is longer than the horizontal distance (A). The greater the slope angle (B), the greater the difference in the distances.

Figure 7.1 – Horizontal distance and slope distance Slope is most often measured in percent or (less commonly) degrees. Slope is read directly from the instrument with no additional calculation necessary. The instrument should be sighted right along the tape used to measure the slope distance.

Any time the slope is 10 percent (5 degrees) or greater a slope correction is required. This is true whether the slope is uphill or downhill. Most electronic height measuring instruments have built-in systems to correct for slope. If a tape (or any other linear measuring device) is used to measure the distance along a slope, a calculation is needed to obtain the necessary slope distance corresponding to the required horizontal distance.

Appendix E contains a table of slope correction factors. When a taped distance is measured along a slope, the required horizontal distance is multiplied by the appropriate correction factor, and the resulting value is the distance that must be measured along the slope.

In order to ensure that the correct horizontal distance is being used, attach the tape to the tree, then move away the required distance and pull the tape tight. Measure the slope of the tape. If it is 10 percent (5 degrees) or greater, multiply the desired horizontal distance by the appropriate slope correction factor from Appendix E and adjust the taped distance to the resulting slope distance.

Example:

Desired horizontal distance 66 feet

Slope to the tree 35%

Slope correction factor (from Appendix E) 1.06

Calculated slope distance 66 feet * 1.06 = 70 feet In order to be a horizontal distance of 66 feet from the tree, the taped distance along the slope would be 70 feet.

7.2 – Height Calculation

It is usually most accurate to measure tree height from a point either uphill from the tree or on the same contour as the tree. Avoid measuring from the downhill side of the tree whenever possible.

Regardless of the point on the tree to which the height is measured, or the instrument used to make the measurements, the method used to calculate the height always uses the same geometry, as described in section 6.1.

Throughout the discussion of height calculations, illustrations will depict height being measured to a spot convenient for demonstrating a concept. These same concepts hold true regardless of the actual spot on the tree to which the height is measured.

7.2.1 – Instrument Above The Tree Base Figure 7.2.1 shows the most common situation where the height measuring instrument is above the base of the tree. The angle to the base of the tree (B) has a negative sign, and the angle to the top (C) has a positive sign.

Figure 7.2.1 – Height measurement with instrument above tree base When the angles have opposite signs the corresponding heights are always added together. Knowing the horizontal distance A and the angle B allows for calculation of the height from the tree base to eye level. Knowing the horizontal distance A and the angle C allows for calculation of the height from eye level to the tree top. These two heights are added together to get the height of the tree.

Example:

Taped distance to the tree 50 feet

Slope to the tree 5% (no slope correction needed)

Angle to tree base -14% Angle to tree top 48%

Tree height (0.14 * 50 ft) + (0.48 * 50 ft) = 31 feet

Example:

A clinometer with a topographic scale is to be used to measure a tree height. A horizontal distance of 66 feet is needed so the topographic scale can be read directly as feet.

Horizontal distance to the tree 66 feet

Slope to the tree 25% (slope correction needed)

Slope correction factor (from Appendix E) 1.03

Taped distance to the tree 66 ft * 1.03 = 68 feet The instrument is moved to a taped distance of 68 feet.

Angle to tree base -21 Angle to tree top

Tree height 21 ft + 55 ft = 76 feet

7.2.2 – Instrument Below The Tree Base Figure 7.2.2 shows the situation where the height measuring instrument is below the base of the tree. The angle to the base of the tree (B) and the angle to the top (C) both have positive signs.

Figure 7.2.2 – Height measurement with instrument below tree base When the angles have the same sign the smaller height is always subtracted from the larger. Knowing the horizontal distance A and the angle B allows for calculation of the height from eye level to the tree base. Knowing the horizontal distance A and the angle C allows for calculation of the height from eye level to the tree top (which is greater than the tree height). The height to the base is subtracted from the height to the top.

Example:

Desired horizontal distance to the tree 100 feet

Slope to the tree 32% (slope correction needed)

Slope correction factor (from Appendix E) 1.05

Taped distance to the tree 100 ft * 1.05 = 105 feet

The instrument is moved to a taped distance of 105 feet.

Angle to tree base 4%

Angle to tree top 76%

Tree height 76 ft - 4 ft = 72 feet

Example:

A clinometer with a topographic scale is to be used to measure a tree height. A horizontal distance of 66 feet is needed so the topographic scale can be read directly as feet.

Taped distance to the tree 66 feet

Slope to the tree 8% (no slope correction needed)

Angle to tree base Angle to tree top Tree height 87 ft - 9 ft = 78 feet

7.3 – Forked Tree The tree height discussions to this point have assumed single, intact, vertical tree stems. There are some special situations that require additional considerations or calculations when measuring tree heights. A forked tree is one such situation.

A tree is said to fork when the bole divides into two or more main stems. The fork is considered to begin at the point where daylight can be seen between the two stems.

7.3.1 – Tree Forked Above 4.5 Feet When a tree forks above 4.5 feet it is considered a single tree. The height of the best fork is measured. This is not necessarily the tallest fork. Figure 7.3.1 shows a forked tree where the height of the fork on the left (to point A) is greater than the height of the fork on the right (to point B). The fork on the right, however, is the better fork due to crook and branching, so the height (C) is measured using the right fork.

Figure 7.3.1 – Height of a forked tree

7.3.2 – Tree Forked Below 4.5 Feet When a tree forks below 4.5 feet it is considered two trees. The height of each stem is measured using the standard procedures.

7.4 – Leaning Tree Tree height is actually a measure of the length of the tree stem. When a tree stands vertically, the height measurement represents this length well. When a tree leans, however, the vertical height is less than the length of the stem.

Whenever possible, a leaning tree should have its height measured from a point perpendicular to the lean. From any other point the height will appear to be different than it actually is. Figure 7.4a illustrates what happens when measuring tree height from a point in line with the lean. The black tree image is leaning toward (image A) and away from (image B) the person measuring the height. The gray tree images show the height that the tree will appear to be.

Figure 7.4a – Improper height measurement - in line with tree lean When a tree leans toward the person measuring its height (image A) the angle to the top of the tree is greater than it would be if the tree were vertical. This causes the estimated tree height to be too large. When a tree leans away from the person measuring its height (image B) the angle to the top of the tree is less than it would be if the tree were vertical.