The desolate scenery and the lack of vegetation and trees are a scene of decline.

This sentence comes from Song Yu's Nine Arguments. Song Yu, a student of Qu Yuan, wrote many poems. The ancients had a tradition of mourning for autumn, mostly from this sentence.

(Supplementary)

I think this is not an allusion, but the poet's experience of autumn, which has been praised by everyone for thousands of years. Song Yu also has an article "Phoenix House", which I think is also very good. As a reference, if possible, look at the Selected Works compiled by Xiao Tong of the Southern Dynasties.