Lecture 10 FORE 3218 Forest Mensuration II Lectures 10 Site Productivity Avery and Burkhart, Chapter 15

Lecture 10 FORE 3218 Definition of Site Quality  Site --The area in which a tree or a stand grows  Site Quality -- Sum of all environmental factors affecting the biotic community of an ecosystem Soil nutrients, moisture, and aeration Temperature regimes Available light Ambient CO 2 concentration Climate and Soil

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 is –Sensitive to site quality –Little affected by stand density and composition –Strongly correlated to volume  Tree height in relation to tree age has been found the most practical, consistent, and useful indicator  Site 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 core  At least 3 site trees are measured, the number depends on ???

Lecture 10 FORE 3218 Chen et al For. Ecol. Manage. 102: Trembling aspen site index curves Site Index Estimation from Total Height and Breast-Height Age

Lecture 10 FORE 3218 Construction of Site-Index Curves  Early site-index curves were constructed by graphical techniques and anamorphic  Anamorphic curves can be constructed by regression techniques

Lecture 10 FORE 3218 Construction of Site-Index Curves  An equation for site index can be constructed Let H=S i.e.,Substitute b 0 into original equation () Rearrange

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 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 qualityGrowth-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 OMNR NEST WP03:

Lecture 10 FORE 3218 Interspecies Site-Index Relationships  Relationships to environmental factors, ecosystem classification, indicators Chen et al Can. J. For. Res. 28:

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 estimate  Concept of site index is not suitable for uneven-aged stands  Site index alone may not provide a valid estimate of the growing capacity for a particular site  Site index may change due to environmental and climatic variations or management activities  Site index for one species can not be translated into a usable index for a difference species on the same site