Understory Cover Percentage

Aggregate area-weighted understory point-layer cover, preserving overlapping layer totals separately from the union; unlike an existing single canopy-area percentage, multiple cover layers are not double counted in union.

Description

Understory layers can overlap at the same point.

Understory layers can overlap at the same point. Summed layer cover can exceed the union cover, which counts each represented point only once.^[1]

When to use Understory Cover Percentage

Use this tool to aggregate area-weighted understory point-layer cover, preserving overlapping layer totals separately from the union; unlike an existing single canopy-area percentage, multiple cover layers are not double counted in union.

Gather the tree inventory, plot measurements or model parameters. Check diameter, area, time and moisture conventions; keep paired observations aligned.

How to use Understory Cover Percentage and understand its results

Gather the tree inventory, plot measurements or model parameters. Check diameter, area, time and moisture conventions; keep paired observations aligned.
Enter pointLayerPresence, representedPointAreasM2 using the field table and calculation rules, then run the tool.
Read layerAreaCoverPercentages, understoryUnionAreaCoverPercent, summedLayerCoverPercent. The explanation below defines the units, signs, ordering and any flags or placeholder values.
If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.

Input field	Meaning	Value type; see rules below	Requirement
pointLayerPresence	Point layer presence	list of list of number	Required
representedPointAreasM2	Represented point areas m2	list of number	Required

Enter a rectangular point-by-layer binary matrix and aligned positive represented point areas. Return area-weighted percentages per layer, any-layer union percentage and summed layer percentages.

Paired lists must be nonempty and have equal lengths.

layer cover=100Σarea × layer presence/Σarea; union uses any layer present

Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.

Output field	Meaning	Value type
layerAreaCoverPercentages	Layer area cover percentages	list of number
understoryUnionAreaCoverPercent	Understory union area cover percent	number
summedLayerCoverPercent	Summed layer cover percent	number

json

{
  "input": {
    "pointLayerPresence": [
      [
        1,
        0
      ],
      [
        1,
        1
      ],
      [
        0,
        1
      ],
      [
        0,
        0
      ]
    ],
    "representedPointAreasM2": [
      1,
      2,
      1,
      2
    ]
  },
  "output": {
    "layerAreaCoverPercentages": [
      50,
      50
    ],
    "understoryUnionAreaCoverPercent": 66.66666666666667,
    "summedLayerCoverPercent": 100
  }
}

Limitations and assumptions

Sampling represents the supplied area only. Summed cover may exceed 100% because layers overlap.

Numeric inputs and returned numeric values must be finite; an unrepresentable returned value produces an error. Matrices are limited to 128 rows and 128 entries per row; other numeric lists are limited to 100,000 entries. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.

Alternative or Complementary methods

Use Plot Occurrence Frequency: Tabulate observed taxon occurrence across assessable plots from a binary inventory; unassessable plots are excluded, not assumed absent, and occurrence is not stem density. For a complementary task, use Crown Competition Factor: Sum caller open-grown potential crown areas under represented stem densities, allowing CCF above 100%; unlike measured canopy union cover, crowns may overlap and widths require independent calibration.

References

Understory Cover Percentage — tool.io

Similar or alternative tools

Plot Occurrence Frequency
Tabulate observed taxon occurrence across assessable plots from a binary inventory; unassessable plots are excluded, not assumed absent, and occurrence is not stem density.
Crown Competition Factor
Sum caller open-grown potential crown areas under represented stem densities, allowing CCF above 100%; unlike measured canopy union cover, crowns may overlap and widths require independent calibration.