Field site description
We conducted our study on four tracts of land within a 16
km2 area of Orleans Parish, southeastern Louisiana,
which we refer to as: “Site B”, “Site H”, “Site M,” and “Site F”
(Fig. 2).
Site B encompasses a 118 ha stretch of second-growth bottomland hardwood
and degraded forest within the Bayou Sauvage National Wildlife Refuge.
This narrow strip of hardwood forest is situated on a natural levee,
causing an elevation gradient from -52 cm to 111 cm as one moves from
the marsh to the forest (Wall and Darwin 1999). It is bordered by a
four-lane highway to the south, a two-lane highway to the east, marsh
and open water to the north, and a gravel road paralleling a large bayou
to the west. The central and northeastern portion of the site is
populated by Chinese Tallow (Triadica sebifera) , Live Oak
(Quercus virginiana) , Bald Cypress (Taxodium distichum ),
and a variety of other wetland tree species. Only a few areas in the
central part of the study site have an abundance of coarse woody debris.
Much of this debris consists of deadfall from Live Oak and Bald Cypress
trees that died following Hurricane Katrina in 2005 (Howard 2012). The
vegetation in the southwestern portion of Site B mostly consists of
emergent vegetation, such as Chinese Tallow, Elderberry (Sambucus
nigra) , and Giant Reed (Arundo donax) . Saw Palmetto
(Serenoa ripens ), a few Live Oak, and Common Hackberry
(Celtis occidentalis ) are also present. The central and
northeastern portions are dominated by Possumhaw holly (Ilex
decidua ), especially at lower elevations, with patches of live oak at
higher elevations.
Site F is located on the east side of the canal bordering Site B. It is
privately-owned land dominated by weeds and vines, such as Blackberry
(Rubus sp. ) and Common Cinquefoil (Potentilla simplex ).
The invasive Chinese Tallow is also present. There are a few scattered
Live Oak, Bald Cypress, and Water Oak (Quercus nigra ) present,
but most of the habitat at this site would best be described as an open
canopy, unmaintained field. At the time of our study, most of the land
was not being maintained, allowing emergent vegetation to become the
bulk of the plant biomass. This site is bordered by a four-lane highway
to the south, a gravel road and a bayou to the east, a small canal to
the west, and a major interstate to the north.
Site H is a privately-owned, 46 ha tract of land located approximately
2.5 km from Site B. Small transects of the property are managed for
hunting activities and New Orleans electric power infrastructure, but
most of the area is unmaintained forest. The forested area is dominated
by Chinese Tallow and is mostly a closed canopy habitat with large
amounts of deadfall. The site is bordered by a levee system to the
south, urban development to the east, a canal and gravel road to the
west, a larger canal to the northeast, and a gravel road and large body
of shallow water to the northwest. Because it is located far from the
natural levee built by the abandoned Mississippi River distributary, it
is an area of low elevation that is sometimes inundated with water
during times of high precipitation or when the water table is higher
than normal.
Site M is an 82 ha tract of privately-owned land located approximately 3
km from Site B. Only a small portion of the northwestern area of this
site is maintained. It has a few grass trails approximately 5 m in width
that are cut with a bush hog pulled by a large tractor biweekly. The
northern and northwestern boundaries are delineated by a canal
approximately 50 m wide and a moderately-used four-lane road. The
northeastern side of the property abruptly turns into a large, grass
field used for cement and rock storage, and further northeast is a large
canal and major interstate. The southern and southeastern areas are
contiguously forested, with the dominant vegetation consisting of
Chinese Tallow, Holly, and Carolina Ash (Fraxinus caroliniana ).
All the forested areas have an abundance of coarse woody debris,
consisting of fallen trees and branches. This site has the highest
elevation and best-drained soils.