Fire is another important element in the maintenance of the Everglades. The majority are caused by lightning strikes from thunderstorms during the wet season. Their effects are largely superficial, and serve to foster further plant growth: sawgrass will burn above water, but the roots are preserved. Fire in the sawgrass marshes serves to keep out larger bushes and trees, and releases nutrients from decaying plant matter more efficiently than decomposition.[20] Large burned areas also affect waterflow, since wind and water are undeterred by the eradicated sawgrass; water may flow two to three times faster in recently burned areas.[21] During the wet season only dead plant matter and the tips of plants are burned; however, the effects of fire are much more significant in the dry season, as fire may be fed by organic peat and burn deeply, destroying root systems. The only impediment to the spread of fire in the Everglades is the presence of water. It takes around 225 years for one foot (0.3 m) of peat to develop, but the peat is not as dense as it should be for the 5,000 years of the Everglades' existence. Scientists point to fire as the reason.[3]