Introduction
Bolivia contains extensive tracts of tropical dry and moist forests that are currently
being subjected to a variety of anthropogenic perturbations, the most important of
which are probably selection logging and wildfire (Fredericksen et al. 2000).
In addition to other impacts, these disturbances may have important effects on
the diversity, composition, and abundance of wildlife (Frumhoff 1995; Johns
1997).
Logging and wildfire occur at various intensities, but both cause tree mortality
resulting in the loss of canopy cover. Canopy opening causes increases in light availability
and temperature within the forest understory and an increase in dead and
downed material on the forest floor, all of which result in modifications of wildlife
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habitat from that existing prior to disturbance (Johns 1997). When logging and wildfire
co-occur within forest stands, extensive canopy opening can result, relegating
areas with closed canopy to fragments within a more open forest matrix (Holdsworth
and Uhl 1997).
Results from research on the impacts of logging and wildfire on wildlife are
accumulating rapidly (see reviews by Whelan 1995; Johns 1997), but the majority
of studies focus on birds and large mammals (Fimbel et al. 2000). Much less
is known about the responses of small mammals, reptiles, amphibians, and invertebrates
to these disturbances. Several studies have shown that small mammal
populations increase in logging gaps, perhaps making use of tangled vegetation for
predator avoidance (Rood and Test 1968; Emmons 1982; Schupp 1988). However,
in a Bolivian dry forest, Fredericksen et al. (1999) found no differences in small
mammal populations among logging gaps and undisturbed areas regardless of gap
size.
Compared to small mammals, even less is known about logging impacts on herpetofauna
and invertebrate populations. Large heliothermic lizards use logging gaps for
basking areas because of their higher insolation (Vitt et al. 1988). Other forest floor
reptiles and amphibians may require higher humidity and more shade than occurs in
logging gaps and other areas without forest canopy cover (Fredericksen et al. 1999).
In trying to explain their observation of more birds in gaps, Schemske and Brokaw
(1981) suggest that the dense vegetation in gaps should attract a rich arthropod fauna,
which would provide a more abundant food source for small mammals and reptiles
and amphibians. However, terrestrial invertebrate abundance was higher in undisturbed
forest than in logging gaps in a Bolivian dry forest, although the responses of
individual taxa varied (Fredericksen et al. 1999).
Because logging and wildfire are pervasive and often linked disturbances in
Bolivia and because they can substantially alter wildlife habitat, it is important to
understand the responses of wildlife to these disturbances. Apparently, little research
has been conducted on these disturbance agents, especially within humid tropical
forests. Although natural fires occur infrequently in humid tropical forests (Sanford
et al. 1985), the impacts on flora and fauna may be greater when fires do occur
compared to drier forests because the vegetation is not as adapted to fire (Uhl and
Kauffman 1990; Mostacedo et al. 1999).
We hypothesized that terrestrial wildlife use disturbed (gaps created by burning
and subsequent logging) and undisturbed areas (forest patches that have not been
altered by logging or burning) with differing frequencies and this use will likely
vary according to habitat preferences of individual species or guilds. We tested this
hypothesis by sampling the small mammal, herpetofauna, and forest floor invertebrate
communities in areas disturbed by wildfire and selection logging and comparing
them to wildlife in adjacent patches of undisturbed forest in a humid tropical
forest in Bolivia. We also examined the effect of seasonal variation (late rainy season,
dry season, and early rainy season) on wildlife use of disturbed and undis29
turbed areas to determine if any interaction exists between disturbance type and
season.