In Ezekiel 26:11, this signifies the love of learning or intellectual things. (Arcana Coelestia 3727)

In Revelation 6:2, this signifies the love of understanding the Word. (Apocalypse Revealed 298)

In Zechariah 12:4, this signifies that the intellectual should be filled with falsities. (Arcana Coelestia 2383[2])

In general, 'a horse' signifies knowledge or understanding of the Word. In an opposite sense it signifies the understanding of the Word falsified by reasonings, and likewise destroyed from self-derived intelligence. 'A dead horse' signifies no understanding of truth from the Word.

Plants in general stand for facts and ideas, so it makes sense that a forest in the Bible represents a collection or system of external, factual, ideas. This can be a collection on its own, or it can be the collected external knowledge of a church. It can also represent the level of a person's mind where he or she deals with such systems of ideas.

(Odkazy: Arcana Coelestia 9011 [1,3-7], 9642 [3,23]; The Apocalypse Explained 650 [26,49])