Lecture 10FORE 3218

Forest Mensuration IIForest Mensuration II

Lectures 10Lectures 10

Site ProductivitySite Productivity

Avery and Burkhart,Avery and Burkhart,

Chapter 15Chapter 15

Lecture 10FORE 3218

Definition of Site Quality Definition of Site Quality

Site Site --The area in which a tree --The area in which a tree or a stand growsor a stand grows

Site QualitySite Quality -- Sum of all -- Sum of all environmental factors affecting environmental factors affecting the biotic community of an the biotic community of an ecosystemecosystem

Soil nutrients, moisture, and aerationTemperature regimesAvailable lightAmbient CO2 concentration

Climate and Soil

Lecture 10FORE 3218

Measurement of Site Quality for Wood-Measurement of Site Quality for Wood-Producing PurposeProducing Purpose

Direct measureDirect measure -historical records of yield -historical records of yield – Historical data do not exist for most sites, and Historical data do not exist for most sites, and – The actual yield can be affected by genetic The actual yield can be affected by genetic

composition, stand density, competition, and pests.composition, stand density, competition, and pests.

The most common indirect methodThe most common indirect method involves involves measurement of tree heightsmeasurement of tree heights

Lecture 10FORE 3218

Tree Height as a Measure of Site QualityTree Height as a Measure of Site Quality

Tree heightTree height is is– Sensitive to site qualitySensitive to site quality– Little affected by stand density and compositionLittle affected by stand density and composition– Strongly correlated to volumeStrongly correlated to volume

Tree height in relation to tree age has been found Tree height in relation to tree age has been found the most practical, consistent, and useful indicatorthe most practical, consistent, and useful indicator

Site index –the measure of site quality Site index –the measure of site quality – The average total height of dominant and co-dominant The average total height of dominant and co-dominant

trees in well-stocked, even-aged stands at a specific trees in well-stocked, even-aged stands at a specific index age, such as 25, 50, or 100 yearsindex age, such as 25, 50, or 100 years

Lecture 10FORE 3218

Methods of Measuring Site IndexMethods of Measuring Site Index

When the subject tree species is presentWhen the subject tree species is present– Application of site index curvesApplication of site index curves– Growth interceptGrowth intercept

When the subject tree species is not presentWhen the subject tree species is not present– Interspecies site index relationshipsInterspecies site index relationships– Environmental factors, ecosystem classification, Environmental factors, ecosystem classification,

indicatorsindicators

Lecture 10FORE 3218

Field Measurement of Site IndexField Measurement of Site Index

Select site treesSelect site trees– which are dominant or co-dominant, even-aged, which are dominant or co-dominant, even-aged,

showing no evidence of crown damage, disease, showing no evidence of crown damage, disease, sweep, crook, forking, or prolonged suppressionsweep, crook, forking, or prolonged suppression

Measure total height with a hypsometer and Measure total height with a hypsometer and breast-height age by extracting an increment breast-height age by extracting an increment corecore

At least 3 site trees are measured, the At least 3 site trees are measured, the number depends on ???number depends on ???

Lecture 10FORE 3218

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0 20 40 60 80 100

Age at breast-height (years)

To

tal h

eig

ht

(m)

Chen et al. 1998. For. Ecol. Manage. 102:157-165

Trembling aspen site index curves

Site Index Estimation Site Index Estimation from Total Height and from Total Height and Breast-Height AgeBreast-Height Age

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25

Lecture 10FORE 3218

Construction of Site-Index CurvesConstruction of Site-Index Curves

Early site-index curves Early site-index curves were constructed by were constructed by graphical techniques and graphical techniques and anamorphicanamorphic

Anamorphic curves can be Anamorphic curves can be constructed by regression constructed by regression techniquestechniques

110ln AbbH d

XbbY 10

Lecture 10FORE 3218

Construction of Site-Index CurvesConstruction of Site-Index Curves

An equation for site index can be constructedAn equation for site index can be constructed

110ln iAbbSLet H=S

110 ln iAbSbi.e.,

)(ln

ln11

1

11

11

i

i

AAbS

AbAbS

Substitute b0 into original equation ( )110ln AbbH d

Rearrange )(lnln 111

id AAbHS

Lecture 10FORE 3218

Potential Problems with Anamorphic CurvesPotential Problems with Anamorphic Curves

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

Anamorphic curves assume that a common Anamorphic curves assume that a common shape for all site classes. shape for all site classes. – For many species, height growth exhibits pronounced For many species, height growth exhibits pronounced

sigmoid shapes on higher-quality sites, and “flatter” sigmoid shapes on higher-quality sites, and “flatter” shape on lower-quality sitesshape on lower-quality sites

Lecture 10FORE 3218

Polymorphic CurvesPolymorphic Curves

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

Additional Reading: Additional Reading: – Chen, H.Y.H., and K. Klinka. 2000. Height growth Chen, H.Y.H., and K. Klinka. 2000. Height growth

models for high-elevation subalpine fir, Engelmann models for high-elevation subalpine fir, Engelmann spruce, and lodgepole pine in interior British spruce, and lodgepole pine in interior British Columbia. Columbia. Western Journal of Applied ForestryWestern Journal of Applied Forestry 15(2): 15(2): 62-69 62-69

Lecture 10FORE 3218

Periodic Height GrowthPeriodic Height Growth

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

Applications in intensively Applications in intensively managed standsmanaged stands

Lecture 10FORE 3218

Interspecies Site-Index RelationshipsInterspecies Site-Index Relationships

Interspecies site Interspecies site index relationshipindex relationship

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

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Site index of white birch (m)

Sit

e in

dex

of

trem

blin

g a

spen

(m

)

Lecture 10FORE 3218

Interspecies Site-Index RelationshipsInterspecies Site-Index Relationships

Relationships to Relationships to environmental environmental factors, ecosystem factors, ecosystem classification, classification, indicatorsindicators

Soil nutrient regime

VP P M R

Site

ind

ex

(m)

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Moderately drySlightly dryFresh and moist

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

Lecture 10FORE 3218

Limitations Using Site Index to Determine Limitations Using Site Index to Determine Site QualitySite Quality

Exact stand age is often difficult to determine in field Exact stand age is often difficult to determine in field situations, and small errors can cause large situations, and small errors can cause large changes in the site index estimatechanges in the site index estimate

Concept of site index is not suitable for uneven-aged Concept of site index is not suitable for uneven-aged standsstands

Site index alone may not provide a valid estimate of Site index alone may not provide a valid estimate of the growing capacity for a particular sitethe growing capacity for a particular site

Site index may change due to environmental and Site index may change due to environmental and climatic variations or management activitiesclimatic variations or management activities

Site index for one species can not be translated into Site index for one species can not be translated into a usable index for a difference species on the same a usable index for a difference species on the same site site