I believe this story may be “The Harmoniser” by <PERSON>. This concerns a (somewhat) sentient tree - the ibis tree - that a powerful alien civilisation had bred to end conflicts.
I read the story in an anthology kind of magazine.
It was first published in Astounding in 1944, but was later anthologised in “Away and Beyond” and “Transfinite: The Essential A.E. van Vogt”.
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.
When the tree detected negative emotions it would produce pheromones that would pacify the aggressor. A ship carrying the tree crashed on the Earth 80 million years ago, and some of the specimens survived (although the aliens tried to destroy as many as possible before they crashed, knowing that the trees could greatly harm the development of the planet). As the ibis tree flourished in its new surroundings, a tyranosaurus fought a brontosaurus nearby:
The initial reactions had begun almost at the moment the dinosaur arrived in the vicinity. Every sensitive colloid of the tree caught the blasts of palpable lusts radiated by the killer… their effect on the delicately balanced films’ of the ibis’ membranes was to set off a feverish manufacture of acids. The ibis tree and its companions exuded a fragrance in the form of billions on billions of tiny dust motes. Some of these motes drifted down to the dinosaur, and were gulped down into its lungs from where, in due course, they were absorbed into its bloodstream.
The effect was that carnivorous dinosaurs stopped killing, and died from starvation. Without population checks the herbivores increased in numbers, and in turn ran out of food and starved. 322
This was the Cretaceous mass extinction.
By the way, by then he was one of the few of his race, still alive.
83 of the trees survived the crash.
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.
The tree was caught in an earthquake and buried:
A continent was rift and torn. The gap was almost a thousand miles long, and in such places as much as twenty-five miles deep. It cut the edge of the island, and plummeted the ibis tree into an abyss three miles deep. Water raged into the hole, and dirt came roaring down in almost liquid torrents. Shocked and buried, the ibis tree succumbed to its new environment. It sank rapidly to the state of a root struggling to remain alive against a hostile force.
Earth was visited by the aliens soon after to dispose of the trees, as their presence would effect the natural evolution of the planet. Because that ibis tree had been buried so deep though, they did not find it. Eventually, many millions of years later, it managed to grow again, in a garden of a soldier and his family. It witnessed the soldier’s angry response to the bomb damage of his house
and less than an hour later began to give off a beautiful perfume.
Soon after, World War III ended. 978