TREE SPECIES-RICHNESS AND TOPOGRAPHIC COMPLEXITY ALONG THE RIPARIAN EDGE OF THE POTOMAC RIVER
Loading...
Links to Files
Permanent Link
Author/Creator
Author/Creator ORCID
Date
1996-10
Type of Work
Department
Hood College Biology
Program
Biomedical and Environmental Science
Citation of Original Publication
Rights
Subjects
Abstract
I studied the riparian forest edge of a central portion of the Potomac River in order to test
whether there is a relationship between small-scale topographic complexity of the
riverbank profile and tree species-richness. A total of 153 transects and 2568 trees were
measured along 60 miles of the Maryland side of the Potomac River corridor between
Harpers Ferry, West Virginia, and Hancock, Maryland. Five-meter-wide strip quadrats
(transects) perpendicular to the river were established systematically at 1/3-mile intervals.
Three tree species, silver maple (Acer saccharinum), boxelder (Acer negundo), and
sycamore (Platanus occidentalis), dominated the species composition of the riparian
edge. Silver maple dominated in terms of overall basal area with over 43 percent, while
boxelder dominated in terms of individuals, with over 38 percent of the stems.
Standardization of species-richness for differing sample sizes was accomplished utilizing
the rarefaction technique, which standardizes on the number of individuals rather than on
unit area. Small-scale topographic complexity was measured by calculating the standard
deviation of 2.5m slope measurements taken along the length of each transect. A
significant positive relationship was observed between tree species-richness and
topographic complexity. However, the low r2 value suggested that change in topography
at a small scale explained only a small part of the variation in species-richness. An
analysis of covariance using adjacent land use designations and underlying geology as
categorical variables, with the standard-deviation-of-slopes as the covariate, indicated that
adjacent land use and bedrock geology had no statistically significant impact on species-richness,
and that the simple linear regression model was adequate to estimate the effect
of topographic complexity on species-richness. Observations made during field work, as
well as a one-way analysis of variance between the different land use/geology groups,
and a rarefaction species-richness analysis of pooled transect data in the Conococheague
Limestone indicated that there were greater concentrations of tree species near cliffs. A
negative relationship was observed between tree species-richness and the width of the
riparian zone, and this relationship was consistent across geology. Tree species
summaries and the location of narrow riparian edges on the outside of meander bends,
suggest that this is an edge effect, due to a greater number of tree species able to take
advantage of an increased light gradient and the presence of a stable, well-drained
substrate not subjected to repeated additions of sediment.