Abstract.-Burning of the forest floor alters the structural
components that constitute the organic substrate. Many small animal
species inhabit this layer, which typically consists of leaf litter from
surrounding trees. The availability of a species' preferred
substrate can be a factor in the rate of recolonization following a
fire. Using pair-wise choice trials within a controlled environment,
preference of substrate typically available after a burn by Scincella
lateralis was determined. These skinks primarily select hardwood leaf
litter and secondarily choose pine needle litter and pine bark slough.
Bare ground was usually avoided. These findings indicate that S.
lateralis may not be able to completely recolonize a site until after
the first seasonal leaf fall following a fire.
The effects of fire on populations of various reptiles have been
well documented (Wilgers & Home 2006; Brown 2001; Granberry et al.
1994). Braithewaite (1987) found that varied fire regimes affect lizard
populations differently, depending on such factors as fire intensity,
duration, and seasonality. Kahn (1960) determined that the presence of
unaltered refuge sites can buffer the effects of fire on certain lizard
populations. For many temperate leaf-litter dwelling species, fire
leaves behind limited and sparse refuge (Watson 2004). The present study
determines the selectivity of the ground skink, Scincella lateralis, to
four substrate components that are available at varying degrees after a
fire in a mixed hardwood/pine forest. Scincella lateralis makes a sound
experimental subject due to the species' abundance, small size, and
limited vagility. This animal is found in temperate wooded areas where
there is sufficient water, cover, and food (Brooks 1967). However, the
leaf-litter layer within the forest, or at forest's edge, is
considered typical habitat for this species (Fitch & von Achen
The ground skink depends on leaf litter and other structural
organic components of the forest floor for refuge (Brooks 1967). The
complete destruction of decaying leaf material may dramatically affect
recovery of this species within burned sites. Conversely, if the ground
skink will utilize pine needle litter or pine bark slough, both of which
are relatively abundant following a fire, it may be able to persist and
recolonize burned sites more rapidly. This experiment aims to determine
the selection of individual ground skinks to four prominent substrate
types found after a burn in a mixed hardwood/pine forest ecosystem in
METHODS & MATERIALS
Six experimental chambers were used, each measuring 32 cm by 77 cm
at the base, providing 2464 [cm.sup.2] of area. This area was uniformly
covered by approximately 3 cm of sifted topsoil. Individual chambers
contained two of the four treatments for habitat preference, each making
up half of the surface area. Substrate treatments, with the exception of
bare ground, were loosely arranged aggregates of the treatment substrate
approximately 5 cm thick. These six chambers cover all of the possible
comparisons for these treatments. The four treatments are as follows:
Hardwood leaf litter.-Whole broad leaves, predominantly from
Quercus sp. This substrate type is generally destroyed in a burn and
will not be present until the following fall. The leaves that make up
this layer are broad and can serve as cover for S. lateralis.
Pine leaf litter.-Needles from Pinus taeda. This substrate type
will be present shortly after a burn and will continue to accumulate
throughout the year. This is due to the fact that the needles of pine
trees are persistent, and their leaf fall is not seasonnaly limited
(Vines 1990). The needles that make up this layer are thin and can only
serve as refuge in aggregate.
Pine slough.-Thin pieces of scorched pine bark that accumulate at
the base of the tree in the months following a burn. The bark pieces
that make up this layer structurally resemble hardwood leaves, providing
broad areas of cover and structure. However, these units are more dense
than comparably sized leaves.
Bare ground.-No large organic substrate present. This represents
the majority of a site's substrate immediately following a burn.
A total of 10 animals of unknown sex (five adults, snout-to-vent
length of 42-51mm; five juveniles, snout-to-vent length of 29-34mm) were
obtained from natural populations in Smith and Dallas counties, Texas.
The organic substrates were collected from sites within Tyler State Park
and heated to temperatures in excess of 65[degrees]C. The elevated
temperatures ensured the elimination of prey items from the material.
This was verified by observation of subsamples of this substrate under a
stereomicroscope. No live invertebrates were noted.
Trials were performed under fluorescent lighting at 27[degrees]C.
Individuals were each transferred to the center of the chamber, with a
treatment to either side of six experimental chambers. The animal was
then allowed a 10-min period of acclimation to the chamber. After this
period, the investigator approached the chamber and marked which
substrate type that the animal was in at time of initial detection. The
skink typically was visible when the chamber was approached, and
immediately retreated to cover. Each trial was repeated 20 times for
Data were analyzed as recommended by Cherry (1998). Confidence
intervals were determined for the mean number of times that a specimen
was observed in each substrate, given equal opportunity to choose
between substrates. There were no significant differences noted between
age groups for any of the treatments. Therefore, the values of both age
classes were combined into one sample to increase power. Significance
was determined between substrates if no values were shared within the
constructed 95% confidence intervals (Figure 1).
RESULTS & DISCUSSION
Bare ground exhibited the lowest mean frequency ([bar.x] = 1.0, 95%
CI: [0.3, 1.7]), and a significant preference was exhibited for hardwood
leaf litter over all three other treatments ([bar.x] = 47.6 95% CI :
[43.2, 52.0]). Pine slough ([bar.x] = 34.3, 95% CI : [30.6, 38.0]) and
pine needle litter ([bar.x] = 37.5, 95% CI : [33.8, 41.2]) exhibited
overlap of the constructed confidence intervals, thereby exhibiting no
significant selection between these treatments.
The top layer of substrate on the forest floor is typically
comprised of dead and decaying organic material. Fire dramatically
alters the makeup of this substrate layer, thereby altering the primary
habitat of S. lateralis. Watson (2004) found, from data gathered in
Smith County, Texas, that the presence of structural organic material is
reduced by over 75% following a fire. Preference for those substrates
that are most decimated by fire may prove to be a limiting factor in
recolonization by this species.
The preference of hardwood leaf litter for cover is consistent with
literature regarding other skink species (Fitch 1954). However, the
three other substrates are the most commonly available in the period
immediately following a burn and preceding the annual leaf fall (Watson
2004). Potential costs to this animal as related to these substrates may
be a factor into substrate selection. The probability of detection of
the ground skink by avian predators is increased in the absence of
refugia (Smith 1997). Pine needle litter does not provide effective
cover unless it is present in aggregate and the density of the pine
slough may not allow for free movement of the lizard when it is arranged
in a compact manner at the base of a tree. Further reasons for the
substrate preferences may be dependant on the availability of prey.
There is little doubt that the acquisition of prey and the ability to
hide from predators play heavily in microhabitat selection.
The preferred microhabitat type for the ground skink is that which
is in shortest supply following a fire. Other factors, such as prey
availability and proximity to undisturbed habitat, may also affect the
recovery of this species following a fire. Invertebrate communities,
which constitute the prey of S. lateralis, are often initially
eradicated with the burning of leaf litter, further tying the recovery
of this species to the return of the leaf litter layer and associated
fauna (Abbot et al. 2002; Bird 1997). Therefore, ground skinks may not
be able to recolonize an area completely until hardwood leaf litter is
present in pre-bum amounts, which may take over three years (Watson
2004). Furthermore, the community structure of the leaf litter layer may
not reach the pre-burn state for many years afterwards, potentially
limiting the full recovery of S. lateralis populations. The recovery of
this species following a burn is nevertheless basically tied to
substrate availability and its timeline for recovery may be delayed for
months following the event, beginning with the first leaf fall and the
associated accumulation of hardwood leaf litter.
I would like to thank Daniel Formanowicz and Laura Gough for their
input and encouragement over the duration of this project as well as
Jessie Meik, Brian Fontenot, and Rebbekah Watson for their
pre-submission editorial expertise.
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Charles M. Watson
Department of Biology, The University of Texas at Arlington
Arlington, Texas 76019
CMW at: email@example.com