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PA SFI Treatment Unit Sustainability Assessment Form (TUSAF)

A sustainable timber harvest ensures the forest will continue to provide its varied and diverse benefits for years to come. So how do you know if your harvesting decisions will result in a sustainable outcome?

In 1995, researchers at Penn State University conducted a study called the Timber Harvest Assessment Project (THAP - see Additional Resources below). They set out to answer three questions; 1) Is harvesting adversely affecting timber sustainability in Pennsylvania? 2) If so, to what extent? 3) What are the causes?

The study examined 97 recently completed harvests across Pennsylvania and evaluated 38 different variables on each site. The study found that almost half of the harvests resulted in unsustainable outcomes based on criteria relating to residual trees (e.g., poor quality, small diameter, species composition shifts, etc.) and regeneration (e.g., inadequate seedling stocking, shifts to undesirable species, competing vegetation, deer impacts, etc.).

Following the study, Penn State University and the US Forest Service developed the Treatment Unit Sustainability Assessment Form (TUSAF) and corresponding TUSAF Sustainability Assessment Key as a way for loggers, landowners, and foresters to assess whether a planned or completed timber harvest will yield a sustainable outcome. Recognizing the potential of this tool for improving timber harvesting outcomes across the state, the Pennsylvania SFI Implementation Committee helped to develop TUSAF into a course that continues to be delivered through our Professional Timber Harvester Training Program today - Sustainable Timber Harvesting.

Research results showed that the answers to a few basic questions about any timber harvesting practice and its context give a great deal of information about its contribution to sustaining Penn's Woods. TUSAF therefore interprets forest data collected using a simple sampling protocol prior to a planned timber harvest to answer seven fundamental questions:

  1. Is the harvest a thinning or regeneration cut?
  2. What will happen to the average stand diameter?
  3. What will happen to species composition?
  4. What will happen to residual tree quality?
  5. What is the condition of the existing advance regeneration?
  6. What is the role of interfering plants (competition)?
  7. What is the impact of white-tailed deer?

The first four questions relate to the residual stand (i.e., the overstory; what you leave) and the last three relate to the regeneration (i.e., the understory; what you establish).

Based on your answers to the seven questions, the TUSAF Assessment Key provides guidance for attaining a sustainable outcome. The Key essentially uses a simplified inventory of assets and liabilities to understand timber harvesting sustainability. When the inventory shows assets outweigh liabilities, the Key finds that the planned harvest is likely to result in a sustainable outcome. When the liabilities outweigh the assets, the Key finds that the operation has problems that are likely to result in an unsustainable outcome. In these cases, the recommendation is to delay the harvest until you resolve the issues. In some cases, the Key will indicate that the results are uncertain and you should seek additional assistance.


Click on the images above to download the Treatment Unit Sustainability Assessment Form (TUSAF) (left) and TUSAF Sustainability Assessment Key (right)

Click on the image above to download the US Forest Service TUSAF course summary publication

Even when you think your harvest will be sustainable, you ought to take the time to assess it. TUSAF provides a quick and easy way to answer questions directly related to timber sustainability. It is a clean and simple tool to help guide your actions and bring about sustainable harvesting outcomes.

Details for understanding how TUSAF works can be found under the Additional Resources listed below.

Additional Resources:

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