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Ernst, K.A., and J.R. Brooks. 2003. Prolonged flooding decreased stem density, tree size and shifted composition towards clonal species in a central Florida hardwood swamp. For. Ecol. & Mgmt. 173:261-279. WED-01-101
Human modifications of the landscape often cause changes in regional
surface and subsurface water flow that in turn can result in
alterations in the natural cycle of flooding and drawdown in wetland
ecosystems. In the present study, excessive flooding resulting from
altered land-use activities increased mortality in wetland tree
communities. We investigated tree decline status, tree size, species
composition, and capacity for clonal propagation along an
elevation/hydrologic gradient to understand community structure and
composition dynamics resulting from excessive flooding.
Prior to disturbance, the density of small stems (2cm
≤ DBH < 10 cm) doubled with a
decrease of <1 m elevation along the transect while density of other
tree sizes (DBH ≥10cm) 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.
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, trees greater than 10 cm DBH were generally more
sensitive to flooding than smaller 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 near permanently flooded
conditions. The mechanism of clonal propagation for surviving severe
flooding events may be important for wetland forest communities
throughout the southeastern US.