The shining summer ages, dwindles, dies;
The heat turns to the cold.
The former azure hue of yonder skies
Is hardly to behold:
...
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You could replace 'bleak boughs' with a straightforward 'branches'? Cheers.
In manuscript the second line of the third stanza reads 'As leaves from bare boughs fall: ' I changed 'bare' to 'bleak', however, for reasons of logic; viz. that the boughs are not bare until the leaves have fallen from them. The same could perhaps be argued for the word 'bleak' but I cannot think of another monosyllable beginning with B that would work.
I could, and that did cross my mind, but I will leave it as it is now. A shade of meaning is lost otherwise. Thank you for the comment though.