FrogLog 103 PDF here - Amphibian Specialist Group

Differences in the Effects of Selective Logging on
Amphibian Assemblages in Three West African
Forest Types
By Caleb Ofori-Boateng, William Oduro, Annika Hillers, Ken Norris, Samuel K. Oppong, Gilbert B. Adum & Mark-Oliver Rödel
Making generalizations about the impact of commercial
selective logging on biodiversity has so far remained
elusive. This is so because species responses to logging
depend on a number of factors, many of which have not been studied
in detail. These factors may include the natural forest conditions
(forest types) under which logging impacts are investigated
but this has been poorly studied.
In a large scale replicate study conducted in south-western Ghana
we aimed at clarifying the relationship between logging and forest
types on leaf litter frogs. We contrast three distinct and naturally
occurring forest types, including wet evergreen, moist evergreen
and semi-deciduous forests. Selectively logged sites were compared
with primary forest sites for each forest type.
Our results revealed a relationship between logging and diversity
in forest types. In the moist evergreen forest, richness and diversity
were higher in selectively logged areas compared with primary forest
sites (due to the influx of invasive non-forest species). In the wet
evergreen forest, richness was higher in logged forest than primary
forest, while diversity measures were not different between logged
and primary forest sites. In the semi-deciduous forest type, a negative
relationship between logging and frog richness and diversity
was observed. Here, logged habitats were characterized by a loss of
forest specialists and low richness and diversity compared to primary
semi-deciduous sites. The timing of logging activity does not
seem to be a factor, since these semi-deciduous sites were logged
just one year before the moist evergreen sites with comparable intensity
to all the other forest types investigated.
We argue that microclimatic differences between logged and primary
habitats may be responsible for generating the different
patterns of diversity observed. Logging in tropical ecosystem typically
involves a significant opening of the forest canopy (1). This
can increase the temperature and reduce humidity on the forest
floor (2). The semi-deciduous forest sites experiences low rainfall
and protracted dry seasons that can significantly increase dryness
of understory leaf litter in logged sites and thus result in unsuitable
conditions for many small leaf litter frogs. Previous studies
suggested that such alteration of the microclimate of the forest
floor can pose physiological constraints on some frog species and
decrease the number of true forest species in altered habitats (3).
In our study, we observed only a single forest specialist species
(Ptychadena aff. aequiplicata) persisting in logged habitats of this
forest type. This frog is among the larger species (3.5 – 6.5 cm)
and hence presumably more tolerant to lower humidity than the
small forest specialists within the genus Phrynobatrachus (usually
around 2 cm body lengths).
Our results highlight the need to contrast the impacts of logging
across different forest types. This can help clarify the relationships
between logging and diversity in forest types and improve our understanding
of logging effects on tropical biodiversity. For future
comparisons of the impact of logging on species to be effective,
research must endeavour to include details of forest type, rainfall
patterns, logging intensities, and rotation cycles.
References
1. A. D. Johns, Biotropica 20, 31 (1988).
2. S. M. Jackson, T. S. Fredericksen, J. R. Malcolm,For. Ecol. Manage. 166, 271
(2002).
3. R. Ernst, M. O. Rödel, Ecology 86, 3111 (2005).
More details
C. Ofori-Boateng, Biotropica, 10.1111/j.1744-7429.2012.00887.x. (2012).
36 | FrogLog 20 (4) | Issue number 103 (July 2012)