I should say that, in addition to my tree-love (it was originally called The Tree), it arose from my own pre-occupation with the Lord of the Rings, the knowledge that it would be finished in great detail or not at all, and the fear (near certainty) that it would be 'not at all'. The war had arisen to darken all horizons. But no such analyses are a complete explanation even of a short story...
Galadriel his sister went not with him to Nargothrond, for in Doriath dwelt Celeborn, kinsman of Thingol, and there was great love between them. Therefore she remained in the Hidden Kingdom, and abode with Melian, and of her learned great lore and wisdom concerning Middle-earth.
I sit beside the fire and think of all that i have seen of meadow flowers and butterflies in summers that have been of yellow leaves and gossamer in autumns that there were with morning mist and silver sun and wind upon my hair. I sit beside the fire and think of how the world will be when winter comes without a spring that I shall ever see. For still there are so many things that I have never seen in every wood in every spring there is a different green. I sit beside the fire and think of people long ago and people that will see a world that i shall never know. But all the while I sit and think of times there were before I listen for returning feet and voices at the door.
If thou hadst thy will what wouldst thou reserve? said Manwe. 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 their 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!
He loved mountains, or he had loved the thought of them marching on the edge of stories brought from far away; but now he was borne down by the insupportable weight of Middle-earth. He longed to shut out the immensity in a quiet room by a fire.