I read the story in an anthology kind of magazine. I can't remember the name. I read the story between 1982 and 1987, I guess. What I do remember was the fact that the tree was vulnerable in the early years. He witnessed a lot of his peers perish, due to animals browsing them excessively. Or floods, fires. He was burned himself too, but not destroyed. When he matured enough, his bulk was sufficient to keep him alive.
And I believe that he had a few tricks up his stem which our earthly trees are not capable off. He had a kind of telepathic link with the animals and other trees around him. As he grew older this power extended until it spanned his total planet. By the way, by then he was one of the few of his race, still alive. If I remember correctly, when the tree was young, he was mobile and ran around the country. When he matured he chose a nice place to take root and saw ages come and go. All the while his intelligence grew.