The 1858 Wright edition replaced the plural forests with the singular forest, but this change was not transmitted into the 1874 RLDS edition (which sometimes follows readings unique to the 1858 Wright edition).
Elsewhere the Book of Mormon text prefers the singular forest when it occurs with beasts or animals:
The Book of Mormon text consistently uses the singular forest when the accompanying preposition is of (“the beasts of the forest” or “animals of the forest”), although it should be pointed out that the two passages in 3 Nephi 20–21 follow (with some variation) the language of Micah 5:8 from the King James Bible, which has the singular forest.
But when the preposition is in, the earliest textual sources can read with either the singular forest (in Enos 1:3) or the plural forests (in 1 Nephi 18:25). Of course, in 1 Nephi 18:25 the beasts would have been found in many different forests, while in Enos 1:3 we can assume that on this occasion Enos was hunting in one particular forest, thus the singular. In any event, when the preposition is in, the context largely determines whether we have forest or forests. (See the discussion for Enos 1:3.)
Summary: Maintain the plural forests in 1 Nephi 18:25 (“beasts in the forests of every kind”); only the 1858 Wright edition has the singular forest.