MobileMap: Stand Summaries

Owned by Tyler Bax
Last updated: Apr 26, 2023 by Kerry Halligan
8 min read

Overview

MobileMap supports offline reporting of stand summary statistics.  These statistics can be useful for evaluating stand attributes while in the field.  They include a range of statistics calculated from the plot and tree data collected for a single stand.  Stand summary statistics do not currently include log-level information.  The following metrics are included in a stand summary report.

  • Stand size (acres)

  • Plot size (BAF or fixe area size in fraction of acre)

  • Number of plots

    • Total number of plots per stand

    • Number of measured plots

  • Number of trees

    • Total number of 'in' trees

    • Number of tallied trees

    • Number of measured trees

    • Ratio of measured trees to total

    • Measured trees by species (total trees, ratio)

  • Trees per plot

    • Average

    • Standard error (%)

    • Min (at selected confidence level)

    • Max (at selected confidence level)

    • Target sample size (at selected confidence level and allowable error level(s))**

  • Basal Area

    • Average

    • Standard error (%)

    • Min (at selected confidence level)

    • Max (at selected confidence level)

    • Target sample size (at selected confidence level and allowable error level(s))**

    • Basal Area by species 

  • TPA

    • Average

    • Standard error (%)

    • Min (at selected confidence level)

    • Max (at selected confidence level)

    • Target sample size (at selected confidence level and allowable error level(s))**

    • TPA by species

  • QMD

    • Average

    • QMD by species

  • Volume

    • Average (per acre)*

    • Total*

    • Standard error (%)*

    • Min (per acre, at selected confidence level)*

    • Max (per acre, at selected confidence level)*

    • Volume (per acre) by species*

* Typically not available. Requires an specifically formatted tree volume database.  More details on generating this database can be provided upon request

** Available at release 4.4.3

Equations

The following equations are used in the calculations described above. They are documented here to help clarify the methodology and the inputs required.

Standard Error / Sampling Error

Standard error is a commonly used metric to quantify the error in the sample mean given the the observed variability in the measured attribute of interest. Standard error gives the accuracy of a sample mean by measuring the sample-to-sample variability and provides insight into how precise the mean of the sample is as an estimate of the true mean of the population. In forestry, it is commonly called Sampling Error and presented as a percent of the mean (denoted E%). The equation below calculates standard error as a percent of the mean:

where:

  • σ = standard deviation

  • n = sample size

  • x̄ = sample mean

Target Sample Size

Target sample size is used to determine the number of samples (e.g., Plots) that would be required to achieve the specified allowable error threshold given the required confidence level and the observed variability in the measured attribute of interest.

where:

  • t = the T value from the 2-tailed Students T Table based on the degrees of freedom (sample size - 1) and the required confidence level (e.g., 95%)

  • cv = coefficient of variation as a percent, calculated as standard deviation / mean * 100

  • ae = allowable error, the error threshold that must be met (e.g., 10%)

Quadratic Mean Diameter

Quadratic Mean Diameter (QMD) is a measure of central tendency which is considered more appropriate than mean for characterizing the group of trees which have been measured. QMD can be helpful when estimating timber volume because it is directly related to basal area, which is directly related to volume (https://en.wikipedia.org/wiki/Quadratic_mean_diameter ).

Where:

BA = Basal Area in ft2

k =constant based on measurement units (0.005454 for BA in ft2 and DBH in inches)

n = sample size (number of trees)

Custom Stand Summary Calculations

MobileMap limited support for user-defined custom calculations within the Stand Summary. These custom calculations include simple criteria or test on one field (e.g., Species = ‘DF’, DBH > 5.5) and simple aggregations (count, min, max, sum, average) on a the same or different field. Custom calculations are entered in a semicolon separated list in the setting Settings > MobileMap Cruise > Stand and Plot Summaries > Custom Stand Summary Calculations.

Syntax for this setting: 'label,fieldname1,operator,value,fieldname2,aggregator;label,fieldname1,operator,value,fieldname2,aggregator;...'

Where: fieldnames are the data model field names (not aliases). The fields can be any String, Integer (short or long) or Decimal (Single or Double) attribute field in the Trees table. Operators for String fields are '=' and '!=', operators for integer and float are '=', '!=', '<' and '>' (without quotes). When fields use coded value domains, the 'value' should match the code not the description. Aggregators include: 'count', 'min','max', 'sum', 'average' (without quotes).

Examples:

  • 'Average DF DBH,Species,=,DF,DBH,average' - will add a line to the Stand Summary that reads 'Average DF DBH: X.X' where X.X will be the average DBH of all DBH trees measured in the stand.

  • ‘Planting Errors,Planting_Errors,!=,NA,Tally,sum' - will add a line to the Stand Summary that reads 'Planting Errors: Y' where Y will be the sum of the planting errors in the Stand calculated using the sum of the values in the Tally field. In this example, the trees table has a field called Planting_Errors which has a value of 'NA’ when there are no errors, and has a list of error types when errors are found. The Tally field is used to record the number of trees that the record represents. This field might default to 1, but can be increased if the record represents more than one tree.

Generate Stand Summary

Steps to generate a stand summary for a stand after measuring plots

  • Select edit tool

  • Select stand layer

  • Tap on desired stand to open

  • Select the Plots Tool

  • Select 'Stand Summary'

  • You will see a message telling you that MobileMap is calculating the stand summary.  Stand summaries can take several minutes to complete if there are a large number of plots and trees.

  • Once the stand summary is complete, it will open in an new screen.  The screen is split in 2 sections, each one can be scrolled up and down.  The top contains stand level summary statistics, while the bottom contains details on each measured plot.

  • To save the stand summary, tap 'Save'.  MobileMap will save the stand summary information (top section of screen shown above) to a text file stored in the Downloads folder of your internal storage.  You can use a text viewer on your device to open and read this report, or send it via mail, copy to a PC, etc.

 

 

Configuration

In order to successfully configure MobileMap to support Stand Summaries, the following settings must be properly set:

Settings > MobileMap Cruise > General

  • Use Tree Sampling

    • Check box to indicate that tree sampling may be used to determine if a tree should be measured rather than tallied.  When enabled, MobileMap will alert cruiser when recording the nth tree so cruiser knows to measure DBH, height, etc.  Complete settings below to define the sampling type field and values representing the different supported sampling types"

  • Stand-Level Sample Type Field

    • Name of field in the Stands table that stores the type of sampling (if any) should be used for a given plot.  Default field name is 'Sample_Type'. MobileMap expects that this field will use a coded value domain with the following values for supporting sampling types: BB = Big BAF, STR = Sample Tree Ratio, FTN = First Tree North, PCM = Point Count or Measure, None = no sampling."

  • Plot-Level Sample Type Field

    • Name of field in the Plots table that stores the type of sampling (if any) should be used for a given plot.  For 'Point Count Measure' approach, sample type at the Stand level will be used to set plots to Count or Measure.  Default field name is 'Sample_Type'. MobileMap expects that this field will use a coded value domain with the following values for supporting sampling types: BB = Big BAF, STR = Sample Tree Ratio, FTN = First Tree North, PCMC = PCM Count, PCMM = PCM Measure, Tally = all trees tallied (same as PCMC, all trees counted and not measured) None = no sampling (same as PCMM, all trees measured)."

  • Tree-Level Sample Type Field Name and Values

    • Name of field in the Trees table (field name should be different than plot-level sample type field) that stores whether tree is a Measure tree or a Tally tree, and the values representing 'measure' and 'tally'. Use colons to separate 3 components.  Typically the values will come from a coded value domain assigned to this field.  Default field name is 'Sample' and values are 'M' and 'T' (e.g., 'Sample:M:T',without quotes).  Note, cannot use non-nullable fields for fields like DHB or Height, since tally trees do not require these measurements (Species and Tally or Count can be non-nullable).

Settings > MobileMap Cruise > Stand & Plot Summaries

  • Enable Calculation of Stand 

    • Check box to enable calculation of stand summaries including BA, TPA and QMD

  • Enable Calculation of Plot Summary

    • Check box to enable calculation of plot summaries including BA, TPA

  • Minimum DBH for average tree per plot calculation

    • Minimum DBH for determining if a tree should be included in the average tree per plot calculation in stand summary.  Default is zero, increasing this value can prevent small trees from having strong impact on average trees per plot calculation."

  • Nested Plots

    • Check box to indicate that a nested plot design is used.  Nested plots are small fixed radius plots used to measure smaller trees.  Use the fields below to indicate the DBH cutoff and area of the nested plot"

  • BAF Limiting DBH

    • Minimum DBH of trees measured on variable radius plots when nested plot design used. This will ensure that trees are assigned to their correct plot/subplot during calculations. This is equivalent to the ‘DBH Breakpoint’ used FVS

  • Nested Plot Area

    • Area of nested plot in fraction of an acre.  For a 1/200th acre plot (radius 8.33 ft) use '200' (no quotes)"

  • Confidence Level

    • Confidence level as a whole number percent. Used when calculating statistics like confidence interval and target sample size. Supported values include 68%, 90%, 95%, 99%. Default is 95%.

  • Allowable Error Value(s)

    • Allowable error used when calculating target sample size. Supports more than one value. Recorded as whole number percent using a comma separated list (e.g., 20,10). When multiple values are used, the stand summary will report multiple target sample sizes, one for each allowable error value.

Settings > MobileMap Cruise > Volume Calculation

  • Tree Volume Database File Name

    • Name of the SQLite database file name to use when calculating volumes (default is 'fvs_nvel_volume.sqlite') and 'dubbing' tree heights.  Database file should be stored in folder named 'Volume' in the main data directory (e.g., '/storage/1234-5678/MobileMap/Volume')

  • USFS Region

    • Select the USFS Region for volume calculations

  • USFS Forest

    • Enter the nearest USFS Forest 3-number code (e.g. 103 for Bitterroot National Forest) for volume calculations.  If volume database created using Region default rather than forest-specific equations, use '1' (no quotes) for region.

  • Volume Unit

    • Select the volume unit to use when calculating tree volumes.