In the opening of Gerald Manley Hopkins' poem Spring and Fall, Margaret is grieving the changing of the seasons. More directly, she is grieving the fact that the leaves are falling at Goldengrove.
It is suggested that she is too young to understand what is happening to the leaves upon the trees. The "death" of the leaves tugs at her heart; all she really understands is that the trees are dying.
Hopkins suggests that as she grows older, she will be able to understand why the seasons change and will come to understand that rebirth is inevitable. Once this happens, she will no longer grieve the changing of the seasons--she will learn to grieve the thigns which are not "renewable" --like the life of a human.