In "A White Heron," the great pine tree is described in Part II.  The narrator says, "the stately head of this old pine towered above [the other trees] and made a landmark for sea and shore miles and miles away."  It is a bit of a mystery as to how the tree survived when all its mates had been felled long ago, but we can begin to understand that this tree is important because it is personified.  Further, the narrator says that it

seemed to lengthen itself out as [Sylvy] went up, and to reach farther and farther upward.  It [...] must truly have been amazed that morning through all its ponderous frame as it felt this determined spark of human spirit creeping and climbing from higher branch to branch.

Thus, the tree is given the human qualities of being able to reach and stretch as well as to feel amazement at the tiny girl climbing so bravely and so high.  By describing it has having survived, alone, for so long in addition to ascribing a consciousness to the tree, it seems to become an important symbol of all nature, nature that is quickly being encroached upon by "civilization."  Just as the hunter is coming to shoot the bird that he loves, loggers have cut down almost all the gorgeous pines.  The value of the tree is emphasized further in its comparison to a ladder reaching up, up, almost to the sky itself."  Little by little, the city is taking over the country, industry is eating up natural resources, and this one great pine serves as a symbol of the innocence and beauty of nature, a nature that is being lost.