In the poem or story, the tree is subjected to various forms of harm, but what ultimately kills the tree is not a single event, but a series of actions. The tree is first subjected to a "simple jab of the knife," a small wound that, on its own, would not be fatal. However, the real cause of its death is the repeated and sustained damage it faces.
The tree suffers from being continually cut and mutilated. As it is chipped away at by the constant cutting, the tree loses its strength, and its ability to heal diminishes. The deep wounds left by the cutting, combined with the ongoing damage, weaken the tree's natural defense mechanisms, making it more vulnerable to other threats.
The final blow that kills the tree is the complete cutting down of the tree. This final act removes the tree’s ability to survive, as it is deprived of its life-sustaining roots, trunk, and branches. The cutting represents the ultimate destruction of the tree, taking away everything that is essential for its life.
In conclusion, the tree is finally killed by a combination of continuous harm, weakening its defenses and ability to heal. The ultimate cause of its death is the complete and irreversible cutting down, which leaves the tree unable to survive any longer.