Selective logging has big, lasting impact on fish

Selective logging has long been considered the lesser evil compared to clear-cutting when it comes to habitat preservation. But a new study adds to a growing chorus of concern that the practice may, in many ways, be just as harmful as outright deforestation. It finds fish communities in forests that were being selectively logged were as harmfully affected as those in clear-cut areas.

For their study, researchers at institutions in the UK and Singapore sampled 23 streams in Malaysian Borneo in forest areas ranging from intact to completely deforested and converted for plantation agriculture. Their results were published last week in Biological Conservation.

The researchers expected to find that fish diversity would scale with the level of land conversion. In other words, they thought streams in protected intact forests would have the most fish species and those in plantations would have the least, with streams in selectively logged forests being somewhere in between.

But that’s not what their findings revealed. Instead, they found nearly as few fish species in selectively logged forests as they did in forests clear-cut for plantations. Meanwhile, protected forests harbored a median number of fish species that was at least twice as high as any kind of logged area.

To fish, it appears, logging is harmful regardless of type.

“That such a small change can impact fish biodiversity is shocking and worrying,” said Clare Wilkinson, a researcher at Imperial College London and lead author of the study. “We expected to see a gradient from least affected in the selectively logged areas, to heavily impacted for the streams in oil palm plantations. Instead, we saw almost the same level of fish biodiversity loss in all altered environments.”

Selective logging operations do not log all trees in a given tract, instead leaving some to stand. The research team chose two kinds of selectively logged areas – those that were logged twice – once in the 1970s and again in the 1990s-2000s – and another that was logged a third time between 2013 and 2015.

They found little difference in the median fish diversity between these two types of logging, despite the twice-logged area remaining unlogged for about two decades. The researchers say this may be due to the fact that fish prefer spawning in shaded areas of streams and that the big, tall trees that provide the most shade are often the ones targeted during selective logging.

For their plantation areas, the team chose oil palm cropland both with and without tracts of forest along streams. Called “riparian buffers” or “riparian reserves” these remnant tracts have been heralded as a way to safeguard at least some portion of native biodiversity in areas deforested for agriculture. In places like Malaysia and Indonesia, which produce most of the world’s palm oil, riparian buffers 15-30 meters in width are required for oil palm operations to obtain sustainability certification.

Previous studies found that riparian buffers may be helpful in maintaining biodiversity – including fish. However, Wilkinson and her team did not find much of a difference between the number of species in oil palm plantation streams with these buffers and those without. The authors say this may be due to differences in the types of habitat they were sampling.

In plantations both with and without riparian buffers, the fish diversity was significantly lower than the researchers were expecting.

The researchers say their results underline the importance of protecting remaining primary forest, and that doing so may not only help safeguard wildlife biodiversity but human communities, as well.

“The freshwater fish in these streams are a food source for local people, so maintaining biodiversity is important. Our study suggests that current protections are not good enough in that they do not prioritise conserving intact forest, and are not sufficient to protect fish in more altered environments.”

 

Citation:

Wilkinson, C. L., Yeo, D. C., Tan, H. H., Fikri, A. H., & Ewers, R. M. (2018). Land-use change is associated with a significant loss of freshwater fish species and functional richness in Sabah, Malaysia. Biological Conservation, 222, 164-171.

Banner image: A researcher samples fish species of the Brantian River in Sabah, Malaysian Borneo. Photo by Clare Wilkinson.

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