Minnesota Technical Notes No. 47: Forestry – Conducting a

This Technical Note replaces Minnesota Technical Notes Woodland No. 19: Woodland Appraisal System, dated April 14, 1969; and Minnesota Forestry Technical Note No. MN-38: Forestry – Woodland Information Stick, dated June 10, 1998.

A forest inventory is performed at Step 3: Inventory Resources, in the NRCS 9-Step Planning Process. Before initiating a forest inventory Steps 1 and 2 need to be completed; Problem Identification and Determine Objectives, respectively. Clients generally visit a field office because they perceive problems in their forest. Before initiating a solution, the forest resources need to be inventoried to determine a baseline condition. Completing the Environmental Evaluation Worksheet NRCS-CPA-52 will help document current resource concerns. (See X document for completing the CAP- 52).

Document the client’s objectives or goals for their forested tracts, and include their level of knowledge about their forest and ecological principles in general. Knowing the client’s objectives creates a goal for planning and management. The more knowledge of forestry or ecological principles the more likely the clients will understand recommended management and implement practices, and more likely to follow through on their plan. Determine and record the level of knowledge on such topics as plant identification in their forest, basic forestry management techniques such as: thinning, regeneration, site preparation, planting or regeneration methods, and the equipment needed for each technique. Discuss concepts of plant community dynamics, soil-plant relationships, tree and shrub selection, how forests react to management practices, forest products and economies, recreation availability, and wildlife habitat needs. Without an understanding of the client’s knowledge of these topics a realistic forest management plan that will be followed is difficult if not impossible to develop.

Once at Step 3, several actions need to be completed before entering the forest. Obtain a copy of the client’s forest management plan if one exists, copies of any receipts for forest management activities such as harvesting, thinning, or , and documents and maps if available from other agencies or consultants the client has used. Find out if there is wildfire history or prescribed burns on the site. Other documents needed are current aerial maps, preferably during leaf-off season, wetland maps, and soil maps. Aerial maps used for planning need to have the typical NRCS mapping protocols. Draw preliminary stand boundaries looking at texture and color cues on the map. (Need an illustration here). Draw roads, farmstead, trails and landings, bridges and fords, firebreaks, evidence of soil or water erosion, and other notable features associated with the forest tracts, and could impact conducting the forest inventory. Plan entrances, parking, exits, and how to get around obstacles, if any. Gather all materials and needed for conducting the inventory (see table x).

At the client’s forest before starting, note the weather, ground cover, topography, soils not marked on a soils map, and grazing condition, type of livestock, numbers, frequency, duration, and forage condition. Determine the main stand or stands. If

necessary, redraw stand boundaries as you go. Record any identifiable paw tracts or scat, dens, and wildlife activity. For measured trees, note those used as den trees (probably rated fair or poor condition). Keep notes on evidence of fire, insect or disease infestation, ground cover changes, and any unusual symptoms in the forest. Take photos to document these conditions.

FOREST INVENTORIES

The type of forest inventory chosen depends on the objective, size, and complexity of the forest. A basic inventory to sample current conditions and composition on 15 acres of an even-aged forest with one main stand can be completed with a zigzag survey by one person. The same size forest, with different forest types, uneven ages and multiple layers would benefit from an inventory that could adequately document the more complex composition and conditions, and would be more efficiently completed with a 2 or 3 person crew using the variable plot sample method. Stands with more complexity may be more resilient and productive. They provide more habitat than stands with less complexity. Structure means structural attributes such as diameter at breast height (DBH*), basal area, tree/ac, etc. Complexity is level of diversity: patchy, dense, or multi- storied. (* need a figure showing how to measure DBH)

Two inventory types will combine speed and efficiency with adequate results suitable for NRCS conservation planning purposes; zigzag transect and variable (radius) plot sampling.

ZIGZAG TRANSECT METHOD

This method is quick and easy requiring few tools, a map and a tally sheet. One person can complete the inventory. Results vary widely depending on the person conducting the inventory due to inherit bias for larger and more desirable tree species. This method is suitable for smaller tracts where a more detailed survey is not needed and one or two transects will provide adequate information for conservation planning. The zigzag transect method is used for determining:

• Average tree diameter • Range of tree diameters • Stocking rate as trees per acre • Stand composition (tree species) • Stand condition or health

Step 1 – Select Main Stand The main stand is usually made up of mature trees at the crown level. Trees to measure are the dominant and co-dominant trees over 4” DBH. Depending on the forest structure, the main stand may be the population younger trees below a few dominant ones. Beneath the main stand there is usually an understory of suppressed trees, advanced reproduction (young trees or seedlings) or herbaceous plants. The client’s

principal concern should be with the main stand no matter in which level it exists. (see Figure x).

Step 2 – Choose a Route Choose a route through the stand so you can sample a good cross section. Generally, this can best be accomplished by crossing the drainageways. On a sunny day you can use the sun as a direction marker by going toward it, away from it, or at some angle to or from it. A visible landmark can also be used as a direct marker. A compass is another that is used to keep on track. Ideally, two or more routes that do not cross or touch are inventoried to cover the whole forested track. If there is an obvious change in forest type, survey each type separately.

Step 3 – Select a Starter Tree The starter tree may be any tree that is a part of the main stand. No measurements are made on the starter tree, it serves only as a point of beginning. Choose a starter tree that is at least 50 feet from a tract boundary, road, cropland, track boundary or open field. Make sure your route will not come any closer than 50 feet from a known boundary.

Step 4 – Choose a Direction At the base of the starter tree, face the chosen direction, place your heels together and position your toes to make a 90-degree angle. A line along the direction of travel bisects the angle formed by your feet (see Figure 2). Using a 90-degree arc such as found on a woodland information stick (or you can make your own zigzag stick, see Figure 3) to help define the angle. When a 25” stick is held horizontally 12” from the eye, the ends of the stick form a 90-degree angle. A compass may also be used.

Step 5 – Locate Closest “IN” Tree Locate the closest main stand tree, the center of which is within the 90° angle. This is tree #1, as shown in Figure 4.

Step 6 – Determine Distance, Species, and Diameter Pace or measure the distance in feet, from the center of the starter tree to the center of tree #1. Determine the species of the tree identified in step 5 and measure its diameter at breast height (4.5 feet, or 4½ feet, or 54 inches, see Figure 5). Record measurements on a tally sheet (see Figure 6).

Step 7 – Rate Tree Condition Examine the tree and rate its condition as good, fair, or poor. A good tree has a reasonably straight single trunk, full crown with no large broken branches, does not have excessive limbs, and does not have evidence of scars, wounds, or disease. A poor tree may have a broken top, 2 or more main trunks below DBH, excessive limbs, cankers, wounds, scars, and disease. Use fair as an intermediate rating but the tree should be sound overall. Do not confuse species desirability with the condition rating. Rate each tree on its own merits without regard to species. Record the condition rating

in the tally sheet or field notes. Describe the reason for rating a tree as good, fair or poor.

Step 8 – Repeat Process Standing at tree #1, repeat steps 5 – 7 to select, measure and rate tree #2. Keep in mind the distance is from mid-trunk to mid-trunk, not closest edge to edge. Continue in this manner until at least 20 trees have been examined. The line of travel will proceed in a zigzag fashion but stays true to the chosen direction as shown in Figure 7. Do not consider or measure dead trees.

Conventions The following conventions are observed when conducting a zigzag transect.

1. Open areas and clumps: Skip over openings and clumps or patches of trees that are not a part of the main stand or are decidedly different in kind or size from the main stand. Do not include spacing measurements or diameter measurements of trees on the edges or openings or clumps. Bypass those trees in the chosen direction of travel and start measurements on the opposite side (See Figure 8).

2. Plantations: In plantations, alternate the direction of travel. Use the direction of the row for the first tree; go at 90° to the row for the second; use the direction of the row for the third, and so on. (Figure 9).

3. Eligible trees: When two eligible trees are equidistant, select the one closest to the direction of travel. Trees joined below DBH are considered separate and individual, and both may be tallied. Determine separately if each tree is “in”. Trees joined above DBH are considered one tree and only one measurement is taken at DBH. In either case, mention that these two (or more) trees are on split trunks on the tally sheet regardless of condition.

Variable (Radius) Plot Sampling

Variable plot sampling does not require measurement of a plot radius required by other sampling method a significant time saver. Each tree is its own plot size dependent on the diameter of the tree. At each center point or “sample point,” a count is made of the number of “in” trees whose diameter is large enough to subtend the fixed angle of the angle gauge or prism. In other words trees that are larger than the angle defined by the angle gauge are “in” trees. See Figure 10 for details on the use of angle gauges and prisms.

In some two aged or two main stands, consider sampling the smaller stand with a 5 BAF angle gauge and the larger stand with a 10 BAF angle gauge. This will save considerable time by reducing the number of trees considered “in”.

With variable plot sampling, no tree measurements are required if only species and basal area are desired. If the number of trees or the volume per unit of area is desired, then the DBH, and height of the dominant “in” trees must be tallied. Trees of any DBH can be sampled, typically only trees of ≥ 4” DBH are sampled. Smaller trees are better sampled on a small plot basis, if needed, see here.

The most important concept to remember in using variable plot sampling is the instrument, angle gauge or prism, remains at the point of plot center, not the person. Use a marker to establish the point of plot center. Rotate the body around the instrument, keeping the instrument at the point of plot center.

If using a prism, always maintain it perfectly horizontal (edge up and down; sky and ground) when viewing the tree. If there is a slope or the tree is leaning, tip the prism to the exact angle of the slope or tip; but keep the prism perfectly horizontal to the sky and ground.

Always measure distance to the center of the trunk not to the leading edge or front of the trunk, unless you want to add some more work to your inventory like subtracting one/half DBH). Borderline trees should be measured from the plot center to trunk center to see if they are in or out. A slope correction table (calculation) using the angle gauge is required on slopes > 10% but are not needed when using the prism.

At the forest have an aerial photo (marked up as above), angle gauge, , compass, 100 foot tape, plot center marker such as a short staff, orange tape or paint, tally sheet, GPS with waypoints.

Step 1 – Choose the Route, Hike to 1st Tree From the points on the map decided in which order you will hike and measure the points taking ease of access into account. The map should show possible forest type boundaries that can be confirmed or changed during the inventory process. Hike to the first plot using GPS coordinates.

Step 2 – Locate the Plot Center Point Using the GPS mark the plot center point with a stake or any object to temporarily mark the plot center point. The significance of this is to ensure that the angle gauge or prism remains at plot center so accurate tree counts are recorded. Is it important to understand that distance is from plot center point to the “in” tree, so the tool needs to remain at plot center point. Standing and revolving your body at the plot center point will result in over counting the “in” trees leading to statistically erroneous results.

Step 3 – Locate Closest “IN” Tree Once at plot center point, there are several ways to start the inventory. One is to start at a cardinal direction such as North as determined by a compass. Mark the 1st tree closest to North, it may or may not be an “in” tree; just so the beginning and end are easily observed. A brightly colored tape, paint or tree marker is used to mark this tree.

Always go in either clockwise or counter-clockwise direction. Whichever way you start, do every plot in the survey in the same direction. Another way to start is to begin with the closest “in” tree and proceed from there.

Step 4 – Determine Species and Distance Start tallying trees as determined by a 10 BAF angle gauge or prism. (add instructions on using these instruments) Start with the marked tree, if the marked tree is “out”, determine a clockwise or counter clockwise direction and move on to the next tree closest to the starter tree, ignore distance, determine in/out for every tree as you move around plot center point. Tally the species and DBH for all in trees.

Step 5 – Rate Tree Condition Examine the “in” tree and rate its condition as good, fair, or poor. A good tree has a reasonably straight single trunk, full crown with no large broken branches, does not have excessive limbs, and does not have evidence of scars, wounds, or disease. A poor tree may have a broken top, 2 or more main trunks below DBH, excessive limbs, cankers, wounds, scars, broken main truck or large branches, and disease or insect infestation. Use fair as an intermediate rating but the tree should be sound overall. Do not confuse species desirability with the condition rating. Rate each tree on its merits without regard to species. Record the condition rating in the tally sheet or field notes. Describe the reason for rating a tree as fair or poor.

Step 6 – Repeat Process By rotating around plot center, keeping the instrument at the plot center point, and moving in the original direction, tally all “in” trees until you complete the circle.

Conventions The following conventions are observed when conducting a variable radius plot survey.

1. Open areas and clumps: If a plot occurs in an open area, do not survey the area as there are no trees to measure. If having a certain number of points is important, another point chosen at random can be added to the survey. If clumps do not contain trees, do not survey the clump. Add a point as above if necessary.

2. Variable radius plot samples are conducted on trees, not shrubs. The minimum sized tree is typically 4” DBH of species that usually form a single stem. If in doubt, measure the DBH to see if the tree should be counted (see instructions). If smaller trees and shrubs are important to measure, use the guidelines for measuring forages found here (Biology HBM).

3. Do not measure dead trees. If wildlife habitat is an important resource concern, separately count dead stumps in each plot. If possible, note what species is/are using the stump.

4. Plantations: There are no special treatments or procedures for sampling a plantation.

5. Eligible trees: If an “in” tree is blocking the view to another tree as seen at plot point center, move off of plot center keeping the distance to the far tree constant until the trunk can be seen to determine if it is “in” or not. You should be moving in a slight arc to maintain the integrity of the plot center point. Trees joined below DBH are considered separate and individual, and both may be tallied, determine separately if each tree is “in”. Trees joined above DBH are considered one tree and only one measurement is taken, at DBH. In either case, mention that these two (or more) trees are on split trunks on the tally sheet.

Insert figures of tools and calculations of DBH.

Appendix: Field Office Resources. In the field office there are important resources to have in your files. Some resources to have on hand are County Comprehensive Plan, State Forest Resource Assessment, Landscape Stewardship Plans… Become familiar with MNDNR landscape plans for your area.