Albert Barnes Commentary Psalms 104:16

"The trees of Jehovah are filled [with moisture], The cedars of Lebanon, which he hath planted;" — Psalms 104:16 (ASV)

The trees of the Lord - From the grass, the herb, the vine, and from bread, all adapted to sustain living beings on the earth, the psalmist transitions to the more lofty and grand productions of the vegetable world. These are the plants that more manifestly display the power of God and furnish shelter and retreats for the various orders of living beings.

The phrase “the trees of the Lord” means great and magnificent trees—just as the expression “mountains of God” means great and lofty mountains—as if they seemed to “approach” God, or as if no name would describe their nature so well as that which was derived from the Infinite One. (See Psalms 36:6, note; Psalms 65:9, note; Psalms 80:10, note).

Are full of sap - The word rendered this way means simply to be full, to be saturated—the words “of sap” being supplied by the translators. The idea is that, as lofty as they are, they are abundantly supplied with what is necessary for their growth. There is no want—no lack—of what is needed to supply them. They flourish, sustained abundantly by what is derived from the earth and the waters.

The cedars of Lebanon - As among the loftiest and most magnificent productions of the earth. (See Psalms 29:5, note; Psalms 92:12, note; Isaiah 2:13, note).

Which he has planted - So lofty and large that it would seem as if only the Almighty could plant them.