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.

402. Verse 13. And the stars of heaven fell unto the earth. That this signifies that the knowledges of good and truth have perished, is plain from the signification of stars, as denoting the knowledges of good and truth (concerning which see above, n. 72); and from the signification of falling unto the earth, as denoting to perish; for when the stars fall to the earth, they perish. The same is signified by, the stars shall fall from heaven, in Matthew 24:29 and in Mark 13:25. Any one may see that by the stars are not meant stars, for these cannot fall from heaven, as they are fixed or stand in their place; neither could they fall to the earth, because they are larger than the earth; therefore such things as pertain to the light of heaven, and give light, which are the knowledges of good and truth, are signified by them. Stars appear also in the angelic heaven, but they are appearances from the knowledges of good and truth, therefore they appear around those who are in those knowledges, especially when they turn them over in the mind, and are in the desire of knowing them.