How does Keats portray nature in 'Autumn'?

From the title we know that nature is going to play a dominant role in Keats' poem Autumn - not only is it the title but Autumn itself becomes a female character when Keats' personifies and apostrophises the season. Keats writes about the beauty of the season and details the beauty of the changing season with rich abundance at almost every turn. The poem later turns melancholic as the season draws to a close and winter approaches. It seems evident that Keats is talking about more than just the season and we see the parallels between the nature of the world and human nature. Perhaps the winter of life and inevitable death has come at the end of the poem and it is this understanding that mars the end of the poem.
//The poem seems simple enough: set in three even stanzas of eleven lines the speaker deals with three distinctly beautiful and autumnal scenes. The form of the poem follows nature's pattern, with each stanza moving the season on . Stanza one describes the beginning of Autumn and by the third stanza we are heralding the end of the season and the coming winter. Perhaps this accounts for the changing tone in the poem and the seeming change of the speaker's feelings towards autumn. Similarly, the rhyme scheme seems simplistic and conventional but on closer inspection we see that it is actual complex and grapples with the speaker's changing and conflicting feelings about the season. The a,b,a,b rhyme scheme does not last long and we are quickly dealing with a scattered but consistent rhyme scheme (a,b,a,b,c,d,e,d,c,c,e) with a half rhyme of the penultimate line of the first stanza adding to the sense of an ending we hear in the word 'cease'. The extra pause given to this word is a clue, even this early in the poem that the season will come to an end shortly and the inevitable winter will return. The lack of enjambement at the end of each stanza reiterates this sense of ending and we are aware the beauty of Autumn, both the season and poem, is finite.
//At the start there is a sense of bounty in the sensual descriptions Keats offers: everything is ' 'fill all [..] with ripeness' and the imagery is of 'sweet' 'plump' and 'budding...flowers'. Clearly autumn's sounds and smells are beautiful and enticing. The reader can be left in no doubt that the speaker has a love and appreciation for the season. The contrast with the last stanza could not be more pronounced. The imagery at the end is much darker and we are left to 'mourn' the passing season which the small robin signifies. It is also notable that all the imagery in the first stanzas are made by nature but that to 'mourn' is a human trait - it is no longer nature alone that Keats is contemplating but also human life. The rhyme scheme changes for the first time in this stanza changing the usual d,c,c,e finishing rhyme for c,d,d,e and this change reiterates the poet's confusion and upset at the end of autumn. All hope is not lost that the end of this poem however, as Keats uses a commn poetic trope to remind us that the seasons will turn again after winter and his question of 'Where are the songs of Spring" will be answered. The 'rosy hue' Keats describes recalls Homer's 'rosy fingered dawn' in the Odyssey and we understand the Keats has paced himself in poetic convention which tells us the days will continue to dawn anew, just as his seasons will.