The effects of flooding on the swamp forest in Lake Ocklawaha, Florida

A 26-km stretch of the Oklawaha River in north-central Florida was impounded in 1968, forming a 5265-ha reservoir and flooding 1620 ha of mixed deciduous hardwood swamp to depths up to 3 m. Carolina ash (Fraxinus caroliniana Mill.), baldcypress (Taxodium distichum [L.] Rich.), red maple (Acer rubrum [L.],) and swamp tupelo (Nyssa silvatica var. biflora [Walt.] Sarg.) were the important tree species, with smaller amounts of cabbage palm (Sabal palmetto [Walt.] Lodd), button bush (Cephalanthus occidentalis L.) and several species of oak and elm. Tree mortality 3 yr after flooding was closely related to water depth, but it alow varied with species and diameter. All trees of all species had died in those parts of the reservoir flooded in excess of 1.3 m. Mortality decreased progressively as prevailing water depth decreased below 1 m. At 0.8 m mortality averaged 41%, 0.7 m it averaged 17%, and at 0.2 m it averaged 2%, about the same as natural mortality in unflooded areas of the swamp. Baldycypress, swamp tupelo, and cabbage palm were the most flood tolerant. The oaks were least tolerant. Measurements at the end of the fourth, sixth, and seventh growing seasons showed that the rate of mortality had dropped to low but still above-natural levels. Under all flooding depths mortality was least in the larger trees, those >38 cm in diameter. Trees