Because wetlands, and the cypress domes that exist in them, help control floods, purify our water and provide habitat and breeding grounds for fish, birds 
(the cypress; domes; ) (wetlands, and the cypress domes; exist; L:in them) (wetlands, and the cypress domes that exist in them; help; control floods)
the cypress wetlands, and the cypress domes wetlands, and the cypress domes that exist in them
domes exist help
L:in them
control floods