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Forest Mensuration II

Forest Mensuration II. Lectures 10 Site Productivity Avery and Burkhart, Chapter 15. Climate and Soil. 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.

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Forest Mensuration II

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  1. Forest Mensuration II Lectures 10 Site Productivity Avery and Burkhart, Chapter 15

  2. Climate and Soil 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 CO2 concentration

  3. 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

  4. 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

  5. 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

  6. 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 ???

  7. Trembling aspen site index curves Chen et al. 1998. For. Ecol. Manage. 102:157-165 Site Index Estimation from Total Height and Breast-Height Age 25 20 15 10 5

  8. Construction of Site-Index Curves • Early site-index curves were constructed by graphical techniques and anamorphic • Anamorphic curves can be constructed by regression techniques

  9. Let H=S i.e., Substitute b0into original equation ( ) Rearrange Construction of Site-Index Curves • An equation for site index can be constructed

  10. 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

  11. 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

  12. 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

  13. Interspecies Site-Index Relationships • Interspecies site index relationship Carmean. 2000. OMNR NEST WP03: 21-39.

  14. Interspecies Site-Index Relationships • Relationships to environmental factors, ecosystem classification, indicators Chen et al. 1998. Can. J. For. Res. 28:1743-1755

  15. 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

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