Poetry of the neck

What is the image of dead trees depicted in couplets and necklaces in poetry? Please summarize and briefly analyze it.

The poet described a withered and useless dead tree. Rotten trunk can pass people, bark is peeling off, and ants are chasing it, so it is "destroyed".

The branches don't even want to throw yellow birds. Only fungi can support it, which shows that it is "useless".