Why are the young trees described as “sprinting”?

The poem has to be perceived through certain mental images which talk about the poet’s psyche. The image of the young trees “sprinting” depict a sense of a fast-moving time. The young trees represent a fresh, rejuvenated childhood spilling into the energetic adulthood. Thus, the “sprinting” young trees suggest passing away of time and entering into the morose and gloomy old age. The “sprinting” of young trees is contrasted against the image of her “dozing” old mother which brings out the paleness and dreariness of death. Thus, the image of the young trees “sprinting” further accentuates the upcoming death.