A timber yield tax is hereby imposed on every timber owner who harvests his timber or causes it to be harvested on or after April 1, 1977, and on every timber owner of felled or downed timber who acquires title to such felled or downed timber in this state from an exempt person or agency described in Section 38104 on or after that date, and on every person who, without authorization, intentionally or unintentionally harvests or causes to be harvested timber owned by another, at the rate of 6 percent of the total immediate harvest value of that timber or at such other rate as may be fixed pursuant to Chapter 3 (commencing with Section 38202) of this part. The immediate harvest value shall be determined as of the scaling date.