We learn in Leviticus 19:23, 24 that the fruit of a new tree is forbidden (orlah) for benefit for its first three years, but all of the fruit from the fourth year is sanctified (revai) and [when the Temple existed] would be brought to the Temple for the Kohanim. Since during shmitah or yovel, the fruit tree owner must declare the fruit that grows on his tree to be hefker (abandoned) and permit the citizens to take fruit to the extent of their personal needs. Accordingly, whould a tree be exempt from the mitzvah of revai if its fourth year fell on a shmitah or yovel year?
Also, since we do not have the Temple anymore, but we still observe shmitah and yovel (well at least some farmers do), what is the practice for dealing with the fruit of a four-year-old tree in a normal year? Is it considered hefker?