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Point Count Measure (PCM)
Point Count or Measure is perhaps the simplest method and uses two different plot types (Measure Plots and Count Plots) within each stand: measure plots and count plots. On measure plots, all trees are measured with sufficient information to calculate tree volume using the selected volume calculations. PCM On count plots, the trees are simply counted. Basal area can be calculated from these count plots, and used with VBAR and TBAR calculations from measured plots to calculate the volume and TPA on the count plots. PCM can be used with fixed area and variable radius plots, but not 100% tally cruises.
First Tree North (FTN)
First Tree North uses a single plot type. When using FTN, the first tree of each sample group is measured on each plot. The 'first' tree is determined by doing a sweep starting facing due North, then rotating clockwise around the plot. The first tree encountered in each sample group is measured. All other trees are tallied. FTN can be used with fixed area and variable radius plots, but not 100% tally cruises.
Big BAF
Big BAF uses a single plot type (like FTN) but two different BAFs. The main BAF is used to determine which trees are 'in' on the plot. The big BAF (often 2 times the BAF of the main BAF) is used to determine which trees on the plot should be measured. Those trees that are 'in' via the main BAF but not 'in' via the Big BAF are tallied. Big BAF has some advantages over First Tree North in that the selection of measure trees is not random within a plot. Big BAF will tend to select the larger trees while this may be biased, it may better represent the higher value trees that the cruiser hopes to characterize with more certainty. Big BAF is only relevant for variable radius plots (not fixed area plots or 100% tally cruises). More information on Big BAF can be found here
Sample Tree Ratios (STR)
Sample Tree Ratios use predefined ratios to select which trees should be measured. Sample Tree Ratios are established for each sample group and applied across the stand (rather than at the plot level like in FTN or Big BAF). An example ratio is 'DF:S:5' which indicates that Douglas fir sawtimber should be sampled at a ratio of 1:5, meaning that one tree should be measured out of every 5 assessed (the other 4would be tallied). MobileMap will always flag the first tree in a sample group as a measure tree, then will use a random component when flagging additional trees. In the previous example, it would flag tree 1 as measure, then 1 tree between trees 2 and 6, 1 tree between trees 7 and 11, etc. STR can be used with fixed area plots, variable radius plots and 100% tally cruises.
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In order to support sampling, several fields must be included in the cruise data model
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Sample_Type
This field should be a text field in both the Plot and Stand feature layers that uses a Coded Value Domain that lists all double sampling methods that are supported, and an option for 'None'. The list of accepted values are:
BB = Big BAF
STR = Sample Tree Ratio
FTN = First Tree North,
PCM = Point Count or Measure
None = no sampling
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. See also the description of these fields at MobileMap: Data Model / Data Modeling Process
Stands and Plots Layers
Big_BAF - Optional
If the Big BAF method is supported, this field should be a text field (length 10) that uses a Coded Value Domain that lists all of the BAF values that are appropriate for Big BAF. Allowed values should follow the same convention
PCM_Ratio Ratio - Optional
If Point Count Measure method is supported, this field should be a text field (length 10) that uses a Coded Value Domain that lists all of the allowed ratios in the format of '1:2', '1:3', '1:4', etc.
STR_Ratios - Optional
if Sample Tree Ratios are supported, this field should be a text field (length 200-500) that will store a comma separated list of ratios (e.g., 'DF:S:5,DF:P:10,GF:XX:2,XX:XX:3'). Both MobileMap and InventoryManager contain tools for authoring sample tree ratios by selecting the species, product and ratio for each sample group.
Stands Table
Sample_Type
This field should be a text field (length 4) and uses a Coded Value Domain that lists all double sampling methods that are supported, and an option for 'None'. The list of accepted values are:
BB = Big BAF
STR = Sample Tree Ratio
FTN = First Tree North,
PCM = Point Count or Measure
None = no sampling
Plots Table
Sample_Type
This field should be a text field (length 4) will be identical to the field in the Stands table unless PCM double sampling approach supported. When PCM supported, the list of accepted values are:
BB = Big BAF
STR = Sample Tree Ratio
FTN = First Tree North,
PCMC = Count Plot
PCMC = Measure Plot
None = no sampling
Trees Table
Tally_Measure Measure - Recommended
This field should be a text field (length 1) in the Tree feature table that uses a Coded Value Domain with the values 'M' for measure and 'T' for tally. MobileMap will update this field automatically when it can determine if a tree should be measured or tallied. Automatic determination of T or M will be possible for PCM, FTN and STR, but not for Big BAF
BAF_Type - Optional
If Big BAF is supported, this text field (length 1) should be present in the Trees feature table and use a Coded Value Domain with the values ‘B' for big and 'S’ for small.
Settings
In addition to these fields, there are a number of settings in MobileMap that need to be configured depending upon which Double Sampling methods are supported
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As described above, the double sampling logic in MobileMap will typically evaluate each tree to determine if it is a ‘measure tree’ (e.g., Tally_Measure field set to 'M'). Business rules then enforce the desired logic for measure trees. Below are some example business rules:
If the field ‘Tally_Measure’ is equal to ‘M' then the field ‘DBH’ cannot be equal to Null
If the field ‘Tally_Measure’ is equal to ‘M' then the field 'Height’ cannot be equal to Null
If the field ‘Tally_Measure’ is equal to ‘M' then the field 'Crown_Ratio’ cannot be equal to Null
If the field ‘Tally_Measure’ is equal to ‘M' then the field 'Form_Class’ cannot be equal to Null
When only Big_BAF is used (not Sample Tree Ratio, First Tree North or Point Count or Measure), business rules would enforce the desired logic for big (B) BAF or small (S) BAF trees. Below are some example business rules:
If the field ‘BAF_Type’ is equal to ‘B' then the field ‘DBH’ cannot be equal to Null
If the field ‘BAF_Type’ is equal to ‘B' then the field ‘Height’ cannot be equal to Null