MBGTools has been updated to support a count:measure cruise design. Previously, MBGTools needed a dbh measurement on every tree, every plot, in order to compile your inventory cruise data. MBGTools can now compile your inventory cruise data with traditional count and measure plot routine (e.g. 1 count plot for every 1 measure plot). On count plots, cruisers only need to tally the number of trees by species. On measure plots, cruisers would collect data for species, dbh, height, taper (optional) and defect.
Tree data on your measure plots are collected and entered into your MBGTools database the exact same way it has always been entered.
Tree data on your count plots are entered into the same tables as your measure plots (SAMPLEPOINTS and CRUISERECS); however, two small differences must be entered into these tables:
1. In SAMPLEPOINTS, list all count plots with a Cruise Type = 'CNT'.
2. In CRUISERECS, list all records on count plots with a Plot Type = 'CO' if trees were tallied and 'CB' if it is a no tally plot.
Example of single species 4 plot cruise:
Suppose a BAF of 20 is used to cruise a stand (of a single species), we record 2 measure plots (Plot Type = IP) and 2 count plots (Plot Type = CO).
Plot Plot Type Tree Count DBH
1 IP 1 6
1 IP 1 8
1 IP 1 10
2 IP 1 11
2 IP 1 15
2 IP 1 10
3 CO 4 NA
4 CO 3 NA
Our compile routine will adjust the compiled TPA for the records in the measure plots so that the sum of the basal area of the trees from the measure plots sums to the sum of the basal area in all plots (before adjusting TPA). This routine is completed for each species.
In our example above:
Plot Number of Trees BA/Acre
1 3 60
2 3 60
3 4 80
4 3 60
Our TPA adjustment factor is then determined calculated as:
BA from all plots = (60 + 60 + 80 + 60) / 4 = 65 square feet per acre
BA from only measure plots = (60 + 60) / 2 = 60 square feet per acre
TPA adjustment factor = 65 / 60 = 1.08333
The MBGTools compile operation will produce the following values in the INVYDATA table:
Plot Plot Type DBH TPA
1 IP 6 55.17
1 IP 8 31.04
1 IP 10 19.86
2 IP 11 16.42
2 IP 15 8.83
2 IP 10 19.86
The compiled records in INVYDATA do not include the tallied trees from the count plots, instead our measure plot tree records have an adjusted TPA to account for the trees on both the measure and count plot using the TPA adjustment factor.
For example, the first tree has a TPA = (BAF / BA / #of measure plots) * TPA adjustment factor = [20 / (6*6*0.005454154) / 2] * (65 / 60) = 55.17
After compiling, the Point Count field in the ADMIN table is set to the number of measure plots.
The methodology of our compile routine is the same result of the standard Volume to Basal Area Ratio (VBAR) method. Therefore, we utilize Bruce's method to calculate the standard error percent:
Percent Standard Error of Basal Area per Acre:
Average basal area per acre = (60 + 60 + 80 + 60) / 4 = 65 square feet per acre
Standard deviation of ba/ac = 10 square feet per acre
Standard error of basal area per acre =10 / sqrt(4) = 5 square feet per acre
Percent standard error of basal area per acre = 5 / 65 * 100 = 7.7%
Similarly, if we have the following cubic foot volumes associated with each tree record, we can calculate a percent standard error using Bruce's method.
Plot Plot Type DBH TPA Cubic Feet
1 IP 6 55.17 3.79
1 IP 8 31.04 8.25
1 IP 10 19.86 12.84
2 IP 11 16.42 17.64
2 IP 15 8.83 34.86
2 IP 10 19.86 12.84
Using Bruce's method, SE%(VOL) = sqrt(SE%(BA)^2 + SE%(VOLBAR)^2).
Where VOLBAR ratios are formed by cubic feet of a tree / basal area of a tree.
For example, the ratio for the first tree is 3.79 / (6*6*0.0054545154), or 19.3
The average of the VOLBAR ratios = (19.3 + 23.6 + 23.5 + 26.7 + 28.4 + 23.5) / 6 = 24.2
Standard deviation of the ratios = 3.1 cubic foot per square foot
The standard error of the ratios = 3.1 / sqrt(6) = 1.3
The percent standard error of the ratios = (1.3 / 24.2) * 100 = 5.3%
Using Bruce's formula, percent standard error for cubic feet = sqrt(7.7^2 + 5.3^2) = 9.3%
These methods are followed to populate the CRUISESTATS table and allow the users to view the Stand Summary Report with confidence intervals.