JWM: Borneo turtles do well when logging is done right

Sustainable logging may help boost a vulnerable freshwater turtle’s occupancy in parts of Malaysian Borneo.

“Despite the negative association with logging with the flat-shelled turtles, they seem to be doing quite well,” said Nick Tan, who recently received his PhD from the Leibniz Institute for the Analysis of Biodiversity Change at the Museum Koenig in Bonn, Germany.

The Deramakot Forest Reserve sits in the northeastern part of Malaysian Borneo. Foresters had heavily logged the area in the past, but in the 1980s, they used a more sustainable method called reduced impact logging. This method is stricter about harvest rates and pays attention to other factors, like the direction a tree will fall. It also requires reduced roads and trails to logging areas and a 30-meter buffer around waterways.

Past studies have shown how this logging practice improved habitat for mammals in Borneo, but researchers hadn’t yet looked at its effect on reptiles there.

Tan’s colleague Sami Asad with the Tomorrow University of Applied Science in Germany had collected field data on reptiles from March to July in 2019. He and an assistant walked transects along eight waterways in Deramakot, recording turtle sightings. Some areas they surveyed had been logged a year prior, while others hadn’t been disturbed for 20 years.

The team collected the most data on two species—the Malayan flat-shelled turtle (Notochelys platynota), considered vulnerable by the International Union for Conservation of Nature, and the Malayan soft-shelled turtle (Dogania subplana), which is more common.

Sustainable logging and freshwater turtles

In a study published recently in The Journal of Wildlife Management, Tan and his colleagues analyzed the data Asad collected to see how sustainable logging was affecting these species. The researchers hoped these findings could help them make further recommendations aimed at decreasing the ecological impacts of the practice.

The team ran occupancy models based on the field sightings of these nocturnal reptiles and took into account factors like the lunar phase, rainfall data taken from nearby weather stations, distance to nearby logging roads, forest canopy height and river size.

The results surprised the researchers—flat-shelled turtles were seen more in Deramakot than the usually more common soft-shelled species. The average occupancy for flat-shelled turtles was 80% compared to 50% for Malayan soft-shelled turtles.

Tan said that the fact that both species have occupancy rates higher than 50% is a good sign for the sustainability of this logging practice.

The analysis also revealed the importance of rainfall for flat-shelled turtle detection. They didn’t appear as much when it was raining—possibly as they lay eggs on sandy banks in drier periods.

The vulnerable species was also found more in larger rivers and in areas that were more than 1,000 meters from a logging road. The logging roads might be affecting the water quality, Tan said, by adding sediment to the rivers—Malayan flat-shelled turtles prefer clearer water.

Fewer Malayan soft-shelled turtles

The data wasn’t as robust for Malayan soft-shelled turtles in this area since the researchers didn’t see as many. But the research revealed a weak trend suggesting that the reptiles seem to appear most about a decade after an area has been sustainably logged. They aren’t found as much during the first 10 years, then they seem to appear a lot more in the 11^th year. After that, the occurrence seems to drop again. Tan cautioned that this data wasn’t as reliable as the trends they found for flat-shelled turtles.

It also isn’t clear why this might be the case and why the researchers found flat-shelled turtles more than soft-shelled turtles. But Tan said that soft-shelled turtles tend to be more tolerant of humans and development—they are often found in urban areas or university campuses, for example.

Neither the lunar phase nor the canopy height seemed to show any trend on turtle occurrence for either species.

Tan said the take-home message from the research is that both species tend to respond well to sustainable logging practices. The data on vulnerable flat-shelled turtles shows how important it is to keep logging roads away from waterways—these should be carefully managed to reduce the impact.

It’s also important to check the weather before conducting surveys, he said. Their data revealed that rainy weather will likely result in fewer sightings.

In the future, he added that it would be good to compare turtle occupancy in these sustainably logged areas with forests that had been more heavily logged.

This article features research that was published in a TWS peer-reviewed journal. Individual online access to all TWS journal articles is a benefit of membership. Join TWS now to read the latest in wildlife research.