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This is a tree downed by logging in Madagascar. Photo credit:
Zuzana Burivalova
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The
selective logging of trees in otherwise intact tropical forests can take a
serious toll on the number of animal species living there. Mammals and
amphibians are particularly sensitive to the effects of high-intensity logging,
according to researchers in the Cell Press journal Current Biology on
July 31 who conducted a meta-analysis of almost 50 previously published studies
from around the world.
"Selective
logging in the tropics is not a new phenomenon, and it will continue to be a
common use of the forest," says Zuzana Burivalova of ETH Zurich,
Switzerland. "We hope that this study will help make selective logging
more biodiversity friendly in the future."
Individually,
those previously published studies had presented an inconclusive and sometimes
conflicting picture of the consequences of the selective removal of trees from
tropical forests, the researchers say. By combining those studies, they hoped
that some overarching patterns would emerge, and indeed they did.
The
new findings indicate that the number of mammal species drops in half at a
logging intensity of about three or
four trees per hectare of forest. Amphibian diversity is halved at a logging
intensity of about six to seven trees per hectare, the
researchers found. (A hectare is a standard unit of land measurement equal to
10,000 square meters, approximately the size of two American football fields.)
Based
on invertebrate surveys, primarily representing butterflies, dung beetles, and
ants, Burivalova and her colleagues found further diversity losses with
logging. Surprisingly, they found that the number of bird species can actually
increase in selectively logged areas, likely because birds lost as a result of
the disturbance are replaced by other, more generalist species.
Burivalova
calls on logging companies to respect logging intensity thresholds that take
biodiversity into account. She and her colleagues say that even forests that
are currently under sustainable management may be logged at intensities that
are far too high for amphibian or mammalian diversity.
"The
current logging quotas are designed predominantly to manage the forest for
sustainable timber production such that a forest will eventually regenerate its
timber stock," Burivalova says. "They are typically not managed for
maintaining faunal biodiversity. This is partly because until now it was not
clear at what point exactly diversity in logged forests starts
decreasing."
She
suggests that consumers can help by paying greater attention to the sources of
the wood in furniture, musical instruments, and other products they buy,
although she notes that this information is often difficult to come by.
Citation
Zuzana Burivalova, Çağan Hakkı
Şekercioğlu, Lian Pin Koh. Thresholds of Logging Intensity to
Maintain Tropical Forest Biodiversity. Current Biology, 2014;
DOI: 10.1016/j.cub.2014.06.065