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PROLONGED FLOODING DECREASED STEM DENSITY, TREE SIZE AND SHIFTED COMPOSITION TOWARDS CLONAL SPECIES IN A CENTRAL FLORIDA HARDWOOD SWAMP
Citation:
Ernst, K. A. AND J R. Brooks. PROLONGED FLOODING DECREASED STEM DENSITY, TREE SIZE AND SHIFTED COMPOSITION TOWARDS CLONAL SPECIES IN A CENTRAL FLORIDA HARDWOOD SWAMP. FOREST ECOLOGY AND MANAGEMENT. Elsevier Science BV, Amsterdam, Netherlands, 173:261-179, (2003).
Description:
Human modifications of the landscape often cause changes in regional hydrology that, in turn, can result in the alteration of wetland hydrology. Altering hydrology can lead to hydroperiods that have prolonged or insufficient hydration, which can often cause changes in plant community structure, composition, and function. In 1996, a large hardwood swamp in Central Florida was noted to have suffered widespread tree-mortality presumably from prolonged flooding. In the present study, wetland tree communities were characterized along an elevation/hydrologic gradient to understand what community structure and composition may have been prior to excessive flooding and how they have changed as a result of increased flooding. Tree size, species, and capacity for clonal reproduction were investigated for effects on survival under varied levels of flood disturbance.
Prior to disturbance, the density of small stems (2 ( DBH < 10 cm) doubled with a decrease of < 1 m elevation along the transect while density of other tree sizes (DBH ( 10 cm) remained relatively constant at all elevations. This increase in small stems corresponded with an increase in the number of individuals growing clonally. Tree communities at the highest elevations were dominated by less flood-tolerant species, such as Quercus laurifolia and Liquidambar styraciflua, whereas tree communities at lower elevations were dominated by highly flood-tolerant species such as Nyssa sylvatica var. biflora and Fraxinus caroliniana.
Changes in community structure and composition as a result of the increased flooding regime were dependent on an interaction between relative elevation and sensitivity to flooding. Prolonged flooding was causing tree communities at low elevations to shift towards a more shrubby structure and composition dominated by more flood-tolerant species that could regenerate clonally. Among most species, larger diameter trees (DBH ( 10 cm) generally were more sensitive to flooding than small trees at high levels of flood disturbance and the ability to reproduce clonally was found to be an important mechanism allowing species such as F. caroliniana and Acer rubrum to persist under nearly permanently flooded conditions.