If you change the primary use of an item
If you buy an item exempt to use in a logging activity, it becomes taxable if you stop using it in a logging activity. You must then pay tax on the fair market value of the item.
Example
You buy a chain saw that you’ll use strictly to cut trees that’ll be sold for lumber. The chain saw qualifies for the exemption because it’s used directly and primarily in a necessary activity. After one year, you replace the chain saw with a new model, and use the old chain saw to cut trees for firewood for your own use. Cutting trees for firewood for your own use isn’t an exempt activity, so the chain saw is now taxable on its fair market value. You must determine the fair market value of the chain saw, and pay use tax on that amount. All parts and supplies to repair and maintain the chain saw from that point on are also taxable.
Note: The opposite isn’t true. If you pay tax on an item because you use it in a non-logging activity, you can’t claim a tax credit if you begin to use it in a logging activity.