At the time that our forefathers came to the Land, [any tree that] they found planted [was] exempt. One that they planted, even though they had not yet conquered, is liable.  One who plants for the public, [it is] liable. R' Yehudah exempts.  One who plants in the public domain, or a non-Jew who planted, or a thief who planted, or one who plants in a boat, or [a tree] that grows on its own —- is liable to orlah.