Several good poems about autumn are Robert Frost's "October," Carl Sandburg's "Autumn Movement" and "September Midnight" by Sara Teasdale. Each one celebrates the beauty of fall while acknowledging the sense of loss it creates.
In "October," Frost describes the fleeting nature of autumn's beauty in the first lines of the poem, "O hushed October morning mild,/ Thy leaves have ripened to the fall;/ Tomorrow's wind, if it be wild,/ Should waste them all." Later, he acknowledges the inevitable progression of time with the lines, "Release one leaf at break of day;/ At noon release another leaf; / One from our trees, one far away./ Retard the sun with gentle mist; / Enchant the land with amethyst./ Slow, slow!"
Sandburg echoes Frost's sentiments in "Autumn Movement" with the plaintive words, "I cried over beautiful things knowing no beautiful thing lasts." At the end of the poem he also pays tribute to the coming winter and acknowledges the inevitability of change with the words, "new beautiful things come in the first spit of snow on the northwest wind/ and the old things go, not one lasts."
In "September Midnight," Teasdale celebrates fall in a different but equally compelling way, describing the incessant chirping of insects on the recently harvested fields. Her words, "Let me remember you, voices of little insects,/ Weeds in the moonlight, fields that are tangled with asters,/ Let me remember, soon will the winter be on us, /Snow-hushed and heavy," also remind the reader that the beauty of fall is short-lived.