I'm into foraging, and foraging questions don't go with cooking advice, so I was wondering how I can preserve staghorn sumac for winter.
If you are talking just about the red seed clusters, then I've found the best way to preserve them is to dehydrate them. I have spread whole clusters in a single layer on cookie sheets and put them in the oven at its lowest setting with good effect. You'll have to leave them in there for a long time. I had mine in there overnight and they still needed more time. I've since switched to a dehydrator which seems safer to me for some reason. The moving air also helps to speed up the dehydration process. Once dry I crumble the "berries" off into containers and then store those in the freezer. They keep for years like that. I suppose you could also vacuum seal them once they are dry, too.
Pro-tip: Try to harvest the clusters while there is still plenty of the white "icing" on the clusters. It tends to appear in late August depending on location, species, and exposure. This is the where most of the tart flavor (Sumac Lemonade) resides, and it is easily washed off in rain.