'If thou hadst thy will what wouldst thou reserve?' said Manwë. 'Of all thy realm what dost thou hold dearest?'
'All have their worth,' said Yavanna, 'and each contributes to the worth of the others. But the kelvar can flee or defend themselves, whereas the olvar that grow cannot. And among these I hold trees dear. Long in the growing, swift shall they be in the felling, and unless they pay toll with fruit upon bough little mourned in their passing. So I see in my thought. Would that the trees might speak on behalf of all things that have roots, and punish those that wrong them!'
'This is a strange thought,' said Manwë.
'Yet it was in the Song,' said Yavanna. 'For while thou wert in the heavens and with Ulmo built the clouds and poured out the rains, I lifted up the branches of great trees to receive them, and some sang to Ilúvatar amid the wind and the rain.'
Then Manwë awoke, and he went down to Yavanna upon Ezellohar, and he sat beside her beneath the Two Trees. And Manwë said: 'O Kementári, Eru hath spoken, saying: "Do then any of the Valar suppose that I did not hear all the Song, even the least sound of the least voice? Behold! When the Children awake, then the thought of Yavanna will awake also, and it will summon spirits from afar, and they will go among the kelvar and the olvar, and some will dwell therein, and be held in reverence, and their just anger shall be feared. For a time: while the Firstborn are in their power, and while the Secondborn are young."
Then Manwë and Yavanna parted for that time, and Yavanna returned to Aulë; and he was in his smithy, pouring molten metal into a mould. 'Eru is bountiful,' she said. 'Now let thy children beware! For there shall walk a power in the forests whose wrath they will arouse at their peril.'
'Nonetheless they will have need of wood,' said Aulë, and he went on with his smith-work.
Just realized, this may be where Bombadil comes from, too.