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Logged but not out: Altered landscapes important for conservation

  • A study conducted by scientists from Malaysia and England looked at biodiversity in untouched and human-altered habitats on the island of Borneo.
  • When the researchers looked at large areas, the biodiversity of big mammals in logged forests closely matched what they found in old-growth rainforest.
  • They concluded that logged forests have substantial value in supporting biodiversity, and these areas should figure into conservation plans.

Ecologists have struggled to peg a value to logged forests for the plants and animals that call them home. They know, for example, that these altered landscapes don’t offer the rich habitats that old-growth forests do, but just how drastically and to what degree has remained a mystery.

Now, a study of mammal biodiversity in Malaysian rainforests published July in the journal Ecological Applications has added to our understanding of what’s happening when we thin a forest. And the conclusions reveal that we might not be giving these areas the credit they deserve.

“We still have a poor idea about the actual mechanisms of biodiversity change in logged forest,” said Oliver Wearn, an ecologist at Imperial College London and the Zoological Society of London and the lead author of the paper. “Is it due to changes in habitat, in resources, or something else?”

An oil palm plantation abuts rainforest in Malaysia. Photo by Rhett A. Butler

To learn more about how forest life responds to logging, Wearn and a team of scientists from England and Malaysia set off into the virgin rainforests, logged forests and oil palm plantations of Malaysian Borneo to see how many mammal species they could find in each of the three habitats. They installed camera traps to count the larger mammals and set live traps to get an idea of what small mammals were living in the different areas.

It’s a fairly common approach to studying human influences on biodiversity, but they also took their work a step further.

“Typically just the number of species is studied, which misses half the story,” Wearn said in an email to Mongabay.

To uncover the other half, Wearn’s team also compared the variety in the species they found at the different locations – that is, how the breakdown of different mammal species changed from one place to another. Ecologists call this type of measurement “beta-diversity.”

“Beta-diversity is really important because it can tell us something about the fundamental processes which generate biodiversity, and if they’re changing due to disturbance” to the forest habitat, Wearn explained. “It’s also really important to think about when we’re designing wildlife reserves.”

Loggers in Sabah State, Malaysia, use heavy machinery to clear forest. Photo by Rhett A. Butler

In the small, localized areas that had been logged, they found fewer big mammals than they did in old-growth rainforest. They anticipated this difference, as presumably the pared-down habitat is not as rich, as they did the drop-off they witnessed on oil palm plantations.

What was interesting is that they found a wider variety when they compared the communities of mammals found at different points in these logged areas than they did in old-growth forests. In other words, the beta-diversity of the logged forest was higher, at least when viewed at this smaller scale.

Wearn attributes this variability in logged forest to the hodge-podge of habitats that selective logging can create. That variation led to more eclectic groupings of mammals species.

“We don’t yet know what effects this might have in the long term, but it may mean we need to think carefully about how we manage these areas,” he said. “We also need to account for this when we’re thinking about how to arrange wildlife reserves.”

Then, when the team zoomed out and looked at these patchwork areas of habitat on a broader scale, the biodiversity variability values from the logged began to coincide with those from old-growth forests, each having around the same numbers of large mammal species.

All of Malaysian Borneo – and the entire island, in fact – is considered a biodiversity hotspot. At the same time, many of Borneo’s rainforests have been logged. A new study highlights the importance of these ‘degraded’ forests for biodiversity conservation.
Sources: Conservation International. “Biodiversity hotspots.” Accessed through Global Forest Watch on 26 October 2016.
Hansen/UMD/Google/USGS/NASA, accessed through Global Forest Watch on 26 October 2016.

That discovery led Wearn and his colleagues to postulate that, to protect the diversity of large animals, the specific location that’s protected in some way – whether through a formal protected area or through a mechanism like a high-conservation-value set-aside that’s part of an agricultural plantation – is less important than just having an area large enough to capture the diversity present in all of these smaller mammal communities. He said he hopes that future research will investigate this question in depth.

It also changes the way we should view logged forest, Wearn said.

“So-called ‘degraded’ forest is actually really valuable for biodiversity conservation,” he said, though he added that we don’t need to create more degraded forest.

“This doesn’t mean we are advocating new logging,” Wearn said. A lot of forested land globally has been touched by logging, and few places is that truer than the island of Borneo. A 2013 study figured that 80 percent had been logged in some way by 2009.

But that doesn’t mean they’re worthless, Wearn cautioned.

“If they’re properly managed – using sustainable logging techniques and by strictly controlling hunting – then these areas could continue to safeguard biodiversity and generate revenue from timber for years to come,” he said.

“If [forests are] converted to oil palm plantations, then these benefits are permanently lost.”