After Halloween, Americans look forward to the Thanksgiving holiday. Pumpkins and corn are often used as decorations during this time.

I wonder if "Pumpkins and corn often serve as decorations during this time" sounds as good as the underlined part.
Sounds okay to me. I wouldn't necessarily choose serve here, as it has so many links with presenting food for consumption, and you're making the point that these food items are not going to be eaten.
Thanks, Rose.