Cutting down even just four trees in a forest can cause extinction –study

Each tree in a forest matters—so much so that the loss of even just a handful could wipe out entire species of flora and fauna forever.

 

New research encompassing some 50 studies worldwide shows that cutting down even just three to four trees per hectare of primary forest already results in species loss, changing ecosystem services (i.e. nutrient cycling), biological resources (i.e. potential sources of medicine), and social benefits (i.e. recreation through birdwatching and hiking) provided by forests. This finding challenges the current management scheme for logging concessions, which only takes into account the sustainability of the timber harvest.

 

Researchers from ETH Zurich, University of Utah, Kuzey Doga Dernegi, Princeton University, and University of Adelaide consolidated data from 48 studies from three continental areas that compared the species richness, or the number of species in an area, of logged areas versus control areas.

 

Logging impact on species richness

 

They showed that the effect of logging on species richness depends mainly on the size of the logged area and what animals are being considered.  

 

Of the four groups studied—mammals, amphibians, birds, and invertebrates—mammals are the most affected by logging, with species richness decreasing once the logged area reaches 10 square meters per hectare of forest. 

 

When the logged area is expanded to 38 square meters per hectare (roughly about three to four trees per hectare) mammal species richness is halved compared to unlogged sites. 

 

Half the amphibian species are lost when logging reaches 68 square meters per hectare, or about six to seven trees per hectare. Invertebrate species richness starts decreasing when 41 square meters per hectare of forest is logged. In contrast to the other animal groups, the species richness of birds showed a net increase after logging. 

 

The researchers suggest that logging affects mammals indirectly through increased hunting and poaching, as logging roads mean easier access into the forest. The removal of canopy-forming trees also makes for hotter and drier microclimates in the understorey, which amphibians don't like. Amphibians are less able to move away from habitats that suddenly become unsuitable. The increase of bird species due to logging was because the forest specialist species were replaced by habitat generalist species.

 

Sustainable timber vs. biodiversity maintenance

 

"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."

 

On which continent the forest is found also affects the rate of species loss due to logging. Forests in the Neotropics (South America) appeared to be more sensitive to logging compared to forests in the Afrotropics (Africa) and Indomalaya (Philippines, Borneo). However, the researchers also noted the lack of studies on the loss of mammal and amphibian species richness in the Indomalayan area.

 

"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." — TJD, GMA News
 

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Macy Añonuevo earned her MS Marine Science degree from the University of the Philippines. She is a published science and travel writer and was a finalist in the 2013 World Responsible Tourism Awards under the Best Photography for Responsible Tourism category. Her writings and photographs may be found at www.theislandergirl.com.