Riverine swamps, like those lining the Pearl River between Louisiana and Mississippi, are the most productive, because the constant flow of water carries fresh nutrients through the system. There is relatively little oxygen in the soil and adjacent leaf litter, and cypress needles, like the needles of other gymnosperms, decompose very slowly. Decomposition is further slowed by the overall reducing chemistry of the swamp floor. This dark color reduces the intensity of sunlight available for photosynthesis, and so reduces primary productivity in stagnant swamps. The gradual accumulation of partially decomposed leaf litter builds up into a thick layer of organic peat.
Peat fires burn slowly, and can smolder on for several weeks.
Fires are rare in the drier swamps, contrary to what you might think. Periodic floods in drier swamps wash away the leaf litter, and prevents the accumulation of a thick blanket of fuel. In the long run, fire helps maintain the cypress swamps, by preventing secondary succession towards a moist hardwood forest. Wind is another important force of disturbance in the swamp. Hurricanes and wind storms can cause a great deal of damage.