Site Index

Site Index is a indirect measure of Forest productivity. In site index we use the height of a tree at a specified base age. Carmean et al. 1989 compiled collection of Eastern United States Site Index curves for 110 species. This function takes parameters for these site index equations and produces a tree specifi site index estimate.

In imperial units:

$$SI = BH + c_1 H^{c_2} \left( 1 - e^{c_3A} \right)^{c_4 H^{c_5}}$$

where: $SI$ is the Site Index in feet, $BH$ is the Breast Height value, $H$ is the total tree height in feet, and $A$ is total tree age in years.

Example

Imperial units
age = 45 yr
height = 70 ft
species = "QUAL"
Answer = 76.10251 ft

Code

Visual Basic

 
Function siteidx(spp As String, age As Single, height As Single) As Double
' Function to calulate the site index estimated from a single tree
' given species using USDA codes, age in years, and height in feet
'
' As presented in "Site index curves for forest tree species in
' the eastern United States" by W. Carmean, J. t. Hahn and R. D. Jacobs
' NCFES General Technical Report NC-128
'
' by David Larsen, Copyright July 21, 2000
' Creative Commons http://creativecommons.org/licenses/by-nc/4.0/us/

If (spp = "QUAL") Then
    ' Carmean, 1972
    bht = 0#
    c1 = 0.3387
    c2 = 1.0135
    c3 = -0.0076
    c4 = -0.9644
    c5 = -0.0176
ElseIf (spp = "QUVE") Then
     ' Carmean, 1972
    bht = 0#
    c1 = 0.2598
    c2 = 1.1721
    c3 = -0.0107
    c4 = -2.3272
    c5 = -0.2825
ElseIf (spp = "QUCO2") Then
     ' Carmean, 1972
    bht = 0#
    c1 = 0.7423
    c2 = 0.9677
    c3 = -0.0223
    c4 = -1.026
    c5 = -0.0137
ElseIf (spp = "mcquilkin") Then
     ' McQuilkin, 1978
    bht = 0#
    c1 = 0.0064
    c2 = 1.6595
    c3 = -0.0003
    c4 = -1.866
    c5 = -0.2916
ElseIf (spp = "upland") Then
     ' Schnur, 1937
    bht = 0#
    c1 = 0.189
    c2 = 1.2031
    c3 = -0.0081
    c4 = -2.1975
    c5 = -0.2582
Else
    si = 0#
    MsgBox ("Unknown species ")
End If

siteidx = bht + (c1 * (height ^ c2)) * (1 - Exp(c3 * age)) ^ (c4 * (height ^ c5))

End Function
Excel® Visual Basic Code

Note the go file has a extra "txt" at the end to allow the files to be viewed in a web browser.


Creative Commons License
Natural Resources Biometrics by David R. Larsen is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

Author: Dr. David R. Larsen, Copyright 2014
Created: August 18, 2014
Last Updated: June 23, 2015