Species Importance Value

Calculate the three-component 0–300 importance-value convention from measured stems, basal area and plot occurrences; not percentage dominance alone or ecological importance certification.

Description

Species importance value combines relative density, dominance and frequency.

Species importance value combines relative density, dominance and frequency. Under the three-percentage convention, scores range from 0 to 300 rather than being a single percentage.^[1]

Calculate the three-component 0–300 importance-value convention from measured stems, basal area and plot occurrences; not percentage dominance alone or ecological importance certification.

When to use Species Importance Value

Use this tool to calculate the three-component 0–300 importance-value convention from measured stems, basal area and plot occurrences; not percentage dominance alone or ecological importance certification.

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

How to use Species Importance Value 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 speciesStemCounts, speciesBasalAreasM2, speciesOccupiedPlotCounts using the field table and calculation rules, then run the tool.
Read relativeDensityPercentages, relativeDominancePercentages, relativeFrequencyPercentages, importanceValueScores. 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
speciesStemCounts	Species stem counts	list of number	Required
speciesBasalAreasM2	Species basal areas m2	list of number	Required
speciesOccupiedPlotCounts	Species occupied plot counts	list of number	Required

Pair nonnegative integer stems/occupied-plot counts and nonnegative basal areas by species. Require each component total positive, normalize each separately to 100 and add corresponding components.

Paired lists must be nonempty and have equal lengths.

importance=relative stem count %+relative basal area %+relative occupied plots %

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

Output field	Meaning	Value type
relativeDensityPercentages	Relative density percentages	list of number
relativeDominancePercentages	Relative dominance percentages	list of number
relativeFrequencyPercentages	Relative frequency percentages	list of number
importanceValueScores	Importance value scores	list of number

json

{
  "input": {
    "speciesStemCounts": [
      10,
      30
    ],
    "speciesBasalAreasM2": [
      3,
      1
    ],
    "speciesOccupiedPlotCounts": [
      2,
      2
    ]
  },
  "output": {
    "relativeDensityPercentages": [
      25,
      75
    ],
    "relativeDominancePercentages": [
      75,
      25
    ],
    "relativeFrequencyPercentages": [
      50,
      50
    ],
    "importanceValueScores": [
      150,
      150
    ]
  }
}

Limitations and assumptions

Plot occupancy and stem density are distinct inputs. Scores do not certify ecological importance beyond this convention.

Numeric inputs and returned numeric values must be finite; an unrepresentable returned value produces an error. Numeric lists are limited to 100,000 entries; the rules above may require smaller limits. 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 Shelterwood Overstory Retention Percent: Summarize matched original/retained overstory basal-area inventories and represented area; not single-tree basal area, canopy cover or a regeneration guarantee.

References

Species Importance Value — 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.
Shelterwood Overstory Retention Percent
Summarize matched original/retained overstory basal-area inventories and represented area; not single-tree basal area, canopy cover or a regeneration guarantee.