Trees around Confucius' tomb

Do you know why there are many trees not of the local varieties around Confucius' tomb even up to today?

In March 479 BC, Confucius fell gravely ill. When Zi Gong came to see him, Confucius was at the gate taking a walk using a stick. Confucious sighed, “The right path under Heaven has been lost for a long time. Nobody wants to adopt my proposals!” Seven days later, Confucius died. The date was March 9, 479 BC.

Confucius' only son Kong Li had already died before him. His grandson Zi Si was still young, so his disciples arranged the funeral. During the mourning period, around their teacher's grave the disciples planted different species of trees fetched from each one's own hometown; hence, the great variety of trees in the woods of Confucius.