Patterns of succession in forested depressional wetlands in north Florida, USA

Abstract

Swamps dominated by the conifer Taxodium distichumvar. nutans (pondcypress) are believed to develop into swamps dominated by a variety of hardwood trees (primarily bays), where organic matter accumulates and fires do not occur. To determine the validity of this long-accepted pattern of succession, relationships among basin characteristics, tree composition, hydrology, soils, and logging history were ex- amined in nine pondcypress swamps and nine bay swamps in north central Florida. Basin depth was defined as the total of maximum standing water and organic matter depth. Shallow basins ( , 65 cm) contained pondcypress-pine (Pinus elliottii) communities; prolonged drought and fire may control the importance of pondcypress within these basins. Medium basins (65-150 cm) ranged in tree species composition from pure pondcypress communities to pondcypress-swamp tupelo (Nyssa sylvatica var. biflora ) communities to bay- cypress communities as organic matter depth increased and standing water depth decreased. Bay-cypress communities that had deeper organic matter than medium-basin pondcypress swamps also had low densities of large pondcypress trees and contained no pondcypress regeneration. Logging in medium-depth basins increased incidence of swamp tupelo and loblolly bay in pondcypress and bay swamps. Deep basins ( .150cm) were dominated by bay communities that did not contain pondcypress. Abundant advance regen- eration of loblolly bay (Gordonia lasianthus) suggests that this species eventually dominates undisturbed bay communities. Total basal area in pondcypress swamps was directly related to organic matter depth (r 2 5 0.53, p 5 0.016, n 5 9), suggesting that growth rate may also be related to this gradient. Productivity of pondcypress may be greatest in medium-basin pondcypress swamps, where deep organic matter leads to faster growth and deep standing water precludes the invasion of hardwoods. Pondcypress does not occur in deep basins. Basin geomorphology appears to play an important role in determining successional seres involving pondcypress and bay trees.