Lecture 10

FORE 3218

Forest Mensuration II

Lectures 10

Site Productivity

Avery and Burkhart,

Chapter 15

Lecture 10

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Lecture 10

FORE 3218

Definition of Site Quality

Site --The area in which a tree or a stand growsSite Quality -- Sum of all environmental factors affecting the biotic community of an ecosystem

Soil nutrients, moisture, and aeration

Temperature regimes

Available light

Ambient CO2 concentration

Lecture 10

FORE 3218

Measurement of Site Quality for Wood-Producing Purpose

Direct measure -historical records of yield Historical data do not exist for most sites, and The actual yield can be affected by genetic composition, stand density, competition, and pests.The most common indirect method involves measurement of tree heights

Lecture 10

FORE 3218

Tree Height as a Measure of Site Quality

Tree height isSensitive to site qualityLittle affected by stand density and compositionStrongly correlated to volumeTree height in relation to tree age has been found the most practical, consistent, and useful indicatorSite index the measure of site quality The average total height of dominant and co-dominant trees in well-stocked, even-aged stands at a specific index age, such as 25, 50, or 100 years

Lecture 10

FORE 3218

Methods of Measuring Site Index

When the subject tree species is present

Application of site index curves

Growth intercept

When the subject tree species is not present

Interspecies site index relationships

Environmental factors, ecosystem classification, indicators

Lecture 10

FORE 3218

Field Measurement of Site Index

Select site trees

which are dominant or co-dominant, even-aged, showing no evidence of crown damage, disease, sweep, crook, forking, or prolonged suppression

Measure total height with a hypsometer and breast-height age by extracting an increment coreAt least 3 site trees are measured, the number depends on ???

Lecture 10

FORE 3218

Site Index Estimation from Total Height and Breast-Height Age

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Lecture 10

FORE 3218

Construction of Site-Index Curves

Early site-index curves were constructed by graphical techniques and anamorphicAnamorphic curves can be constructed by regression techniques

Lecture 10

FORE 3218

Construction of Site-Index Curves

An equation for site index can be constructed

Lecture 10

FORE 3218

Potential Problems with Anamorphic Curves

Anamorphic curves constructed using paired temporary height vs. age data can be biased because in many timber types young stands are associated with generally better sites

Why?

Anamorphic curves assume that a common shape for all site classes.

For many species, height growth exhibits pronounced sigmoid shapes on higher-quality sites, and flatter shape on lower-quality sites

Lecture 10

FORE 3218

Polymorphic Curves

Polymorphic: family of site index curves display differing shapes for different site-index classes

Additional Reading:

Chen, H.Y.H., and K. Klinka. 2000. Height growth models for high-elevation subalpine fir, Engelmann spruce, and lodgepole pine in interior British Columbia. Western Journal of Applied Forestry 15(2): 62-69

Lecture 10

FORE 3218

Periodic Height Growth

Growth-Intercept Method The use of height growth for some relative short period during the life of the stand to assess site quality

Applications in intensively managed stands

Lecture 10

FORE 3218

Interspecies Site-Index Relationships

Interspecies site index relationship

Carmean. 2000. OMNR NEST WP03: 21-39.

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Site index of white birch (m)

Site index of trembling aspen (m)

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DBHNumber of treesNumber of trees

Lecture 10

FORE 3218

Interspecies Site-Index Relationships

Relationships to environmental factors, ecosystem classification, indicators

Chen et al. 1998. Can. J. For. Res. 28:1743-1755

Lecture 10

FORE 3218

Limitations Using Site Index to Determine Site Quality

Exact stand age is often difficult to determine in field situations, and small errors can cause large changes in the site index estimateConcept of site index is not suitable for uneven-aged standsSite index alone may not provide a valid estimate of the growing capacity for a particular siteSite index may change due to environmental and climatic variations or management activitiesSite index for one species can not be translated into a usable index for a difference species on the same site

Lecture 10

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Lecture 10

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Age at breast-height (years)

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Soil nutrient regime

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