Complex sentence: Rawhide is also used to cover saddle trees, which make up the form or foundation of a western saddle, while wet: it strengthens the wooden tree by drawing up very tight as it dries.
Split into simpler sentences: Rawhide is also used to cover saddle trees, which make up the form or foundation of a western saddle. The wet rawhide is used to strengthen the wooden tree by drawing up very tight as it dries.