How to Calculate Sustainable Yield

Sustainable yield is a term applied across a variety of industries, but particularly in forestry and logging. In its simplest form, sustainable yield tells you how much timber can be harvested from a forest while maintaining the overall capacity of the ecosystem. Sustainable yield also takes into account that the harvesting of timber, or whatever product you're extracting, is done regularly and consistently over a given period of time. However, it is important to consider that once a tree is logged, part of the ecosystem has been damaged--energy, shelter and shade are gone and will not be replaced immediately in the same location.

Things You'll Need

• Computer with Excel
• Forest management and data collecting instruments

Instructions

1. Research information on the existing forest ecosystem. Look for information like the net productive area of mature and over-mature forest, the standing net volume of grade D+ sawlog for the mature and over-mature forest, the net productive area of regrowth forest, age of the regrowth section of forest, and the mean annual increment of regrowth.

2. Calculate the long-term productivity potential of the forest. Do this by multiplying the net productive area of both the mature and over-mature types of forest by the mean annual increment of regrowth for the specified plot of land under consideration for management.

3. Maximize the long-term potential for forest productivity by establishing a balanced age class distribution of each section of land under management. This is only available if there is one main species in the section of forest to be managed through sustainable yield. You must use a much more complex method of calculation for forest sections with a wide variety of tree species, since each species has its own growth characteristics and niches. And there will be an uneven distribution of age classes if the area has been use in the past for logging or if it has experienced major fires.

4. Determine the level of harvest that can be sustained to provide a non-declining supply of D+ sawlog. This means the rate of logging should be constant over a period of time, usually one year. This should also account for how long the existing regrowth forests will take to reach the minimum harvest age. The rate of harvest should allow loggers to cut the over-mature forest sections first, moving on to the younger forest sections last so that there will no interruption in logging activity. This is advisable not only for the environment to begin recovering but also so that the logging industry can employ its workers consistently.

5. Schedule the harvesting of forest sections and trees. Whenever possible, sections of forest should be cut when they have reached the nominal rotation age rather than the minimum harvest age. If the minimum harvest age is logged, that may affect the overall capacity of the ecosystem to produce long-term recovery.

6. Recheck the sustainable yield on a regular basis. Environments and ecosystems often change without our being aware of the changes. Unknown and unforeseen circumstances could affect the ability of the forest to renew itself. Re-estimate sustainable yield regularly to make sure the forest is in fact regenerating at the expected rates.

Tips & Warnings

• Methods used to calculate sustainable yield change over time according to management strategies. Further research can reveal the usability of newer or older models for calculating sustainable yield in a specific forest environment.

• More advanced methods of estimating sustainable yield will also take into account the accessibility of the forest sections to be logged, requirements for recreation use, water production, and conservation.

References

• Review of Sustainable Yield Rates
• Maintenance of productive capacity of forest ecosystems
• Determination of Sustainable Yield

Resources

• Designation of Sustainable Yield Units
• Estimation of Maximum Sustainable Yield
• Simple Methods for Calculating Minimum Diameter and Sustainable Yield