What are "Atzei Hashem"?
Rashi: They are [the trees] in Gan Eden.
Radak #1: The Semichus to "Hashem" shows that they are the tall trees. Verses often put matters next to Kel to show that they are great and awesome, e.g. "k'Harerei Kel" (36:7), "Shalheves Kah" (Shir ha'Shirim 8:6), "Ir Gedolah lEi'lokim" (Yonah 3:3).
Radak #2: The Semichus to "Hashem" shows that they sprout and grow without man's involvement. After mentioning Esavim and trees that grow with man's work, it mentions these, which grow via Hashem's will alone.
What satiates "Atzei Hashem"?
Radak: It is the rain mentioned above - "Mashkeh Harim me'Aliyosav" (verse 13).
Why does it say "Arzei Levanon Asher Nata"?
Radak: It mentions cedars, for they are the tallest forest tree. "Asher Nata" teaches that man does not plant them, like he plants fruit trees for his needs. Rather, Hashem put nature in the land to produce them for the needs of the creations. Hashem waters them from Aliyosav, and they are satiated; man need not water them. There are also forest trees that the land produces without man's work, such as apples and oak.
