2 Establishing Plots – Point Sampling A cruise method where the sample trees are selected proportional to their basal area. Thus larger trees sampled in greater proportions.Fixed angle projected from plot center to determine ‘IN’ treesPlay video
4 ProcedureThe basal area factor (BAF) selected needs to yield an average of 5 to 12 trees per point.Do not use a smaller BAF resulting in more sample trees per point. The coefficient of variation (CV) may not be reduced but may result in missed trees. A larger BAF will result in fewer sample trees per point but cause the coefficient of variation to increase.Use only one BAF for a particular stratum.Larger BAF for larger trees. Western softwoods might use 20 to 60.In Kentucky, a BAF of 10 usually fits.
5 How many points? Rule of Thumb If area in acres is: Number of points should be:Less than 10: 1011-40: 1 per acre41-80: * (area in acres)81-200: * (area in acres)
6 Basal Area Factorindicates the number of square feet of basal area/acre each "in" (measure) tree represents.
7 Basal Area Factor (BAF) Each sample tree, regardless of DBH, represents the same basal area per acre for a given critical angle. This constant is the basal area factor (BAF) of the angle gauge.In fixed area sampling, when using circular plots, the plot radius is fixed for a plot of a given size. For example, the plot radius for a fifth-acre plot is 52.7 feet. Each tree, regardless of size, on a fifth- acre plot is associated with a plot radius of 52.7 feet.
9 Common BAF and PRF used in the United States kPRF
10 Plot Radius FactorCan use to calculate limiting distance to determine ‘IN’ trees
11 Plot Radius Factor = 8.696/SQRT(BAF) Which means:For each inch of DBH, a tree can be 2.75 feet from the point to stillbe included in the point’s tally.
12 Limiting DistanceSince a basal area factor of 10 has a plot radius factor of we know that any tree farther away than 2.75ft * DBH from our point center will be considered out.We measure the distance from point center to the middle of the tree (not the point facing side)
14 Variable Plot Another way of looking at it is as a multiplot. Each tree has its own plot, whose size is dependent on the diameter of the treeThose trees whose plots overlap the center point get measured.How many trees at this point will be tallied?
15 Slope Limiting Distance 1. Measure the diameter to the tenth of an inch2. Determine the horizontal limiting distance from the face of the tree (HLD = PRF X DBH)3. Determine the percent of slope from the face of the tree at DBH to where the wire pin or wooden stake penetrates the ground.4. If the slope is 10% or greater, correct the horizontal limiting distance to slope limiting distance (SLD). To obtain the slope limiting distance, multiply the horizontal limiting distance by the appropriate slope correction factor (SCF). (SLD = HLD X SCF)5. Use a tape graduated in tenths of feet to measure the distance from the face of the tree at DBH to plot center. The plot center is where the wire pin or wooden stake enters the ground. These are two exact points that can be measured "to" and "from". If the measured distance is equal to or less than the slope limiting distance, the tree is "IN" and is sampled. If no slope correction is needed, the horizontal limiting distance is compared to the measured distance.
16 Slope Limiting Distance Slope Correction Factor X Horizontal Limiting Distance = Slope Limiting DistanceSCF X HLD = SLD
31 Thumb as an angle gauge Let thumb width = 0.85” Eye to thumb distance = 25”BAF = ft2/acreTry this at home
32 “IN” Trees (determined then measured) Fixed PlotVariable Plot
33 Problem TreesForked Trees - Use measurement rules to determine if measuring one or two trees and to determine diameter. Then calculate limiting distance.Leaning Trees - Angle gauges are always used by looking at the diameter of a tree at breast height. When a tree is leaning to the left or to the right, as viewed from point center, the angle gauge is tilted so it is oriented along the axis of the tree rather than vertically. If the tree is leaning toward or away from point center, the angle gauge is held as it would be for a vertical tree. If a limiting distance calculation is required for a leaning tree, the distance from point center to the tree is measured to the center of the tree at breast height, just like it is for vertical trees.
34 Problem TreesDown trees -- Trees of this nature are determined to be "in" or "out" depending upon the location of DBH in relation to the plot center and the appropriate limiting distance. That is, all measurements are made between the plot center and DBH and the tree is "in" or "out" regardless of root location, etc.Hidden trees -- It is possible that a tree or some other object obscures the view of a tree behind it. A cruiser must be careful to recognize this possibility and check to see if there are any hidden trees which could be "in" trees. If there is an obscured tree which might be "in", the cruiser moves away from point center in a direction perpendicular to the direction to the tree just far enough to be able to clearly see the tree at breast height. The same rules then apply as for any other tree.Distant Large Trees
35 Null PlotsMust be tallied as having no trees for correct expansion factor to apply to whole site.
36 Boundary Points – Half points The simplest method for dealing with boundary points is also the most prone to bias. Basically, an imaginary dividing line is drawn through the point center in such a way it does not cross the boundary. Only those trees whose center point is on the side of the line away from the boundary are considered. Since this represents only half a regular point, every tree that is "in" is recorded twice.
37 Boundary Points – Quarter points If a point center falls near a corner or other area where even a half point is not possible, the quarter point method can be used. This method is basically the same as the half point method except two imaginary lines extend at a right angle from the point center in such a way that they do not cross the boundary. The only trees considered are in the area between the two imaginary lines. Since this represents only a quarter of a point, every tree that is "in" is recorded four times.
38 Boundary Points - Mirage Points 1. Establish plot2. Measure all trees within the plot that are in the unit3. Measure distance from plot center to boundary4. Set mirage plot center on the same line at an equal distance outside of unit boundary5. Establish a second plot of equal size from mirage plot center6. Rerecord all trees in the mirage plot which are also in the original plotMirage points should not be used where the boundary is curved or irregularly shaped. In addition, someone must be able to actually stand at the mirage point center. What situations would exclude the use of this type of point?
39 Boundary Points - Walkthrough points Least Biased and Easy to useWorks for curvy boundariesFor any tree that is "in", measure the distance from the point center to the tree then measure that same distance beyond the tree. In other words, walk through the tree the same distance the tree is from point center. If the ending point is outside the boundary the tree is recorded a second time. It also works even if a person can't go beyond the boundary.
40 Point Sampling Summary It is not necessary to establish a fixed plot boundary; thus greater cruising speed is possible.Large high-value trees are sampled in greater proportions than smaller stems.BA and volume per acre may be derived without direct measurement of stem diameters.When volume-per-acre conversions are developed in advance of fieldwork, efficient volume determinations can be made in a minimum of time. Thus the method is particularly suited to quick cruises.Does not work well in heavy underbrush.
42 Basal Area per AcreBA per acre = (total trees tallied/no. of points) X BAFSum total for cruise and also sum by species(93/12) X 10 = 77.5 sq ft per acreFrequency of stems tallied by DBH and Height classes from 12 point samplesBAF = 10Height (no. of logs)DBH(in.)123Total10207271282540145151641128461993
43 Trees per acre – single tree example .oo5454 X DBH2 = ft2 Area of treeIf DBH = 12 thenX 144 = .785 ft2 area for that treeBAF / ft2 Area of tree = trees per acreUsing a BAF of 1010 / .785 = 12.7 trees per acre represented by each 12 inch DBH tree
44 Trees per AcreTrees per acre = no. trees tallied X per-acre conversion factor total no. of pointsMust be calculated for eachTree size then summed for entiretract
45 Trees per acre - Example Frequency of stems tallied by DBH and Height classesHeight (no. of logs)DBH(in.)123Total1020727128254014515164112846199310-in. class = 27(18.35)/12 = 41 trees per acre12-in. class = 40(12.74)/12 = 42 trees per acre14-in. class = 15(9.35)/12 = 12 trees per acre16-in. class = 11(7.16)/12 = 7 trees per acreTotal = 102 trees per acre
46 Volume-Factor Approach (Part 1) Create a table of the calculations from previous slide18.35 X 39 = 716And so on Board-foot volume by 16-ft logsDBH(in.)1231039631259981271414118616190256Board-foot volume per acreHeight (no. of logs)DBH(in.)123107161156127521248161814131817391613601833
47 Volume-Factor Approach (Part 2) Board-foot volume per acreHeight (no. of logs)DBH(in.)123107161156127521248161814131817391613601833Volume per acre = (20 X X 1156+ 8 X X X 1618+10 X X 1318+ 4 X X 1833)/12 points = 9258 board feet per acre
48 Volume/Basal-Area Ratios Approach (Part 1) Basal Area = .005454 (DBH)2 Board-foot volume by 16-ft logsDBH(in.)1231039631259981271414118616190256Basal Area by 16-ft logsDBH(in.)12310.54512.785141.069161.396For 10 inch, 1 log tree the ratio = 39/.545 = 72Populating the table with the remaining calculations…Board-foot volume per sq ft of basal area by 16-ft logsDBH (in.)123107211612751251621413217416136183
49 Volume/Basal-Area Ratios Approach (Part 2) Board-foot volume per sq ft of basal area by 16-ft logsDBH (in.)123107211612751251621413217416136183Volume per acre = (sum of ratios/no. of trees) X BA per acreSum of ratios =20 X X X X X X X X X 183 = 11126Recall BA per acre was the easy calculation at the beginning of all this –BA per acre = total trees tallied/no. of points X BAF = 93/12 X 10 = 77.5 sq ft per acreVolume per acre = 11126/93 X 77.5 = 9272 bd ft per acreDiffers from 9258 found earlier due to rounding errors.