23.2
m
1.291
23.2
m
1.291
The Site Index Calculator estimates the productive potential of a forest site by projecting the height of dominant trees to a standard reference age. Site Index is the single most important indicator of site quality in forestry: it reflects the combined influence of soil, climate, and topography on tree growth. Higher Site Index means the site supports faster height growth and greater timber productivity.
Enter the current dominant height, tree age, the base age for your region (commonly 50 or 25 years), and the species growth coefficient. The calculator projects height to the base age using a simplified power-function model.
The calculator uses a simplified site index model based on height-age relationships:
Site Index = Height x (Base Age / Age)b
Where b is a species-specific growth coefficient (typically 0.3-0.8) that describes the shape of the height-age curve. When the tree is younger than the base age, the ratio is greater than 1 and the height is projected upward. When the tree is older, the ratio is less than 1 and the effective height at the base age is estimated as lower than the current height.
This is a simplified guide curve model. More precise site index estimation uses species-specific polymorphic equations that account for differing growth patterns across site qualities.
Inputs
Results
Pines at 18 m height at age 30 project to a Site Index of 23.2 m at base age 50, indicating a productive site.
Inputs
Results
Hardwoods at 28 m at age 60 project back to 25.6 m at age 50, a high-quality site.
Base age varies by region and species. In North America, 50 years is standard for most timber species, while 25 years is used for fast-growing plantation species. In tropical forestry, 20 or 25 years is common. European forestry sometimes uses 100 years for slow-growing species. Use the base age that matches the site index curves published for your species and region.
Dominant height (the average height of the tallest trees in a stand) is used because it is relatively insensitive to stand density and thinning history. Average height can be reduced by overstocking or increased by heavy thinning. Dominant height growth is primarily controlled by site quality, making it a more reliable indicator of inherent site productivity than average height.
The growth coefficient b determines how height scales with age. A value of 0.5 means height grows roughly proportional to the square root of age. Species with rapid early growth and early height plateau have lower b values, while those with sustained height growth have higher values. Use species-specific b values from published growth models for your region, or consult a forest mensuration textbook.
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The Roboculator Team explains calculations, planning tools, and practical formulas in clear language for real-life situations.
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