In general, trees represent the deepest and most significant intellectual concepts: the ones that come to us most directly from the Lord. This varies depending on us and our states: the people of the Most Ancient Church, who were in a state of loving the Lord, understood truth automatically and internally through what the Writings call "perception"; people in lower states (including most of us) have to work a little harder to learn it from the Word and by willing to follow the Lord. In other parts of the Bible, especially in the prophets and New Testament parables, the meaning of "tree" is broader, meaning not just a person's intellectual concepts but the whole person.

'Trees,' as in Joel 1:10-12, signify knowledges.

122. Internal Meaning of Lamentations, Chapter 4

1-3 Holy truths and goods turned into falsities, (3, 4)

4 so that there is a lack of all of them. (3)

5-8 Their spiritual things have become infernal. (3)

9-10 Affections of truth have become cupidities of falsity. (3)

11 They were against the Lord. (3, 4)

12-14 They falsified the truths of the Word. (3)

15 It was impure. (3)

16-17 The Word was rejected owing to their own intelligence. (3, 11)

18-19 Nothing of the church was left, and therefore came their destruction. (3)

20 The Lord was rejected. (9)

21-22 The external of the church was also vastated. (3)