If this was not part of a timber farm, then enter it as an Investment.
If you received money from the sale of timber, you'll probably get a Form 1099-S. Some people will get a 1099-MISC, which is (technically) the wrong reporting form per the IRS.
Regardless of which form you received, timber income is reported in the investment section. Follow these instructions. Don't enter the sale in the 1099-S or 1099-MISC section or you'll go down the wrong path.
On the Choose the type of investment you sold screen, you'll want to select Everything else, located at the bottom of the screen. For your cost basis, most people will enter a 0, but you could enter what you originally paid for the seedlings or saplings.
Tip: TurboTax doesn't support IRS Form T (Timber), but the good news is that you probably don't need this form. According to the IRS, it's only needed "...when a sale or deemed sale under sections 631(a), 631(b), or other exchange has occurred during the tax year." See the IRS instructions for Form T.
