Cypress can tolerate having their roots submerged all year but they grow 10 times as fast when their roots are only damp year around. I know this because ARMF & FEI planted many hundreds of ~ 1 foot tall cypress in 2003 in an area with a 12 month hydro-period and one with a 0 month hydro-period. Those in the 12 month hydro-period marsh are now 3 – 5 feet tall and those in the 0 month hydro-period adjacent to the marsh are now 30- 50 feet tall!
Last summer we visited areas along the Gulf Coast where the USACE has kept the marsh from having a seasonal cycle of very wet to almost dry and the cypress are dying. cheers, Dr. Tom