Dominant Height Calculators

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Dominant height — also called top height — is a fundamental measurement in forestry that describes the average height of the tallest or largest trees in a stand. Unlike mean height, dominant height is largely unaffected by thinning and competition, making it a stable and reliable indicator of a site's productive potential. It is the primary input for site index calculation, the standard measure of forest quality used worldwide for yield prediction, species selection, and timber valuation. If you work in forestry, ecology, or silviculture, understanding dominant height is non-negotiable.

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What Is Dominant Height?

Dominant height (also called top height) is the average height of a specified number of the largest or tallest trees per unit area in a forest stand. The most common definition uses the 100 trees with the greatest diameter at breast height (DBH) per hectare, though some systems use the tallest trees or trees in the dominant and co-dominant crown classes.

The key advantage of dominant height over simple mean height is its insensitivity to stand density. When trees are thinned, mean height changes significantly because shorter, suppressed trees are removed. Dominant height, however, changes little — the top trees are rarely removed in thinning operations. This makes it a consistent, comparable measure across stands with different management histories.

Why Dominant Height Is Used in Forestry

Dominant height is the foundation of site index (SI) — the most widely used measure of forest site quality:

Site Index = Dominant Height at a reference age (usually 50 or 100 years)

A higher site index means the site supports faster growth and higher timber yields. Site index allows foresters to:

  • Compare the productivity of different forest areas objectively
  • Select the most appropriate tree species for a given location
  • Predict future stand volume and plan harvest rotations
  • Value forest land for purchase, investment, or conservation

How to Measure Dominant Height

In the field, dominant height is measured using:

  • Clinometers and hypsometers: Optical instruments measuring height by trigonometry from a known horizontal distance
  • Laser hypsometers (e.g., Vertex, TruPulse): Measure distance and angle simultaneously for faster, more accurate results
  • Airborne LiDAR: Laser scanning from aircraft or drones generates canopy height models across thousands of hectares

The process involves identifying dominant and co-dominant trees in a sample plot, measuring their heights, and calculating the average for the defined number of trees per hectare.

Dominant Height Growth Curves

Dominant height increases rapidly in young stands and slows as the stand matures, following an S-shaped trajectory over time. Site index curves — developed for specific species and regions from long-term permanent plot data — chart dominant height against age for different site quality classes. Common mathematical forms include the Chapman-Richards, Schumacher, and polymorphic height-age equations.

Dominant Height vs. Other Height Definitions

  • Dominant height (top height): Average of the largest/tallest trees — best site quality indicator, insensitive to density
  • Lorey's height: Basal-area-weighted mean height — gives more weight to larger trees than a simple average
  • Arithmetic mean height: Simple average of all measured trees — most sensitive to thinning and stand history

Glossary

Dominant Height (Top Height)
The average height of the largest-diameter or tallest trees in a forest stand, typically defined as the 100 trees with the greatest DBH per hectare. The primary input for site index calculation.
Site Index (SI)
A measure of forest site quality defined as the dominant height of a stand at a given reference age (usually 50 or 100 years). Higher site index values indicate more productive sites with faster tree growth potential.
Height-Age Curve
A species-specific growth curve showing how dominant height changes with stand age for different site quality classes. Used to determine site index from a single height and age measurement in the field.

Frequently Asked Questions

Dominant height is the average height of only the largest or tallest trees in a stand — typically the 100 trees with the greatest DBH per hectare — while average tree height is the mean of all trees. Dominant height is preferred in forestry because it doesn't change much when suppressed trees die or are removed, making it a more stable and reliable indicator of site productivity over time.

Site index is the dominant height a stand is expected to reach at a standard reference age — usually 50 or 100 years. It is the primary measure of forest site quality and productive potential. A higher site index indicates faster tree growth and higher timber yields. Site index is read directly from species-specific height-age curves using a measured dominant height and known stand age.

The most widely used convention is the 100 trees with the largest DBH per hectare (40 per acre in imperial systems). In some European systems, the 100 tallest trees per hectare are used instead. The specific definition varies by country, forest type, and management tradition, so it's important to specify which definition is being used when comparing dominant heights across studies.

Yes. Airborne and drone-mounted LiDAR (Light Detection and Ranging) can accurately measure dominant height across large areas by generating detailed 3D canopy height models. LiDAR-derived dominant height estimates correlate strongly with field measurements and are increasingly used in operational forest inventories, carbon stock assessments, and growth monitoring programs.