Effect of canal blocking on biodiversity of degraded peatlands: Insight from West Kalimantan

PLOS One | https://doi.org/10.1371/journal.pone.0334014 October 8, 2025 14 / 23 Passive acoustic monitoring led to detection of finer scale differences in disturbed wet shrub when compared to results from the point-count and line transect surveys. Acoustics indices (particularly ADI, AEI, and BI) differentiated disturbed wet shrub and forested areas, and similarity with estate crop. Since frequency range used to calculate acoustics indices can also detect insect vocalization, it is possible that more insect species were detected, thus increasing the diversity [81–83]. Passive acoustic monitoring resulted in the same environmental and habitat features as explanatory variables, that more likely to directly affect taxa detection rather than to the actual number of acoustic indices [84]. The differing methodologies employed in our study complement each other, providing a comprehensive understanding of the habitats under investigation. Direct sighting of wildlife provides a baseline to conduct macro taxa detection during acoustic analysis. In addition, the continuous audio recording allows us to capture any species present which we did not encounter in person due to limitations in conducting continuous human observation. The calculation of acoustic indices also granted a direct approach to acoustic diversity as complementary approach to assessing to biological diversity, although interpretation requires careful considerations. We did not use camera traps in this survey due to security con-

cerns, the lower probability of immediate results within our study timeframe, and the shorter detection range. If possible, the further study can apply camera trap to complete human observation and acoustic monitoring because it is useful in capturing non-vocal animal, particularly mammals [85]. During our surveys, the only restoration effort observed for degraded peatlands was canal blocking. This involved constructing dams to retain water and reduce rapid drainage during the dry season, ultimately aiming to raise the water table and restore the hydrological function of the peatland after extensive canal construction had drained it [86]. However, a study on peat rewetting in a boreal landscape reported that while improvements in water storage and runoff dynamics were observed, full hydrological recovery was not evident within the first three years [87]. Canal blocking has also been successful in preventing fire and haze in several locations [88,89], but our sites have yet to experience the benefit. This was highlighted by a fire that occurred at our sites and their surroundings on August 23, 2024, when this study was con- ducted, posing a threat to biodiversity. Furthermore, when considering the direct impact of canal blocking on biodiversity in our sites, there is insufficient evidence to suggest its effect on wildlife diversity in all habitats. The higher wildlife diver- sity observed in forested areas appears to be influenced by their complex vegetation structure, which creates an ideal

microclimate and resource availability for the wildlife. In contrast, non-forested habitats have lower wildlife diversity due to their open conditions and limited vegetation structure, which do not provide a suitable environment for a diverse range of species. Nevertheless, the fact that vegetation, regardless of its woody trait, can still be found in estate crop sites and disturbed wet shrub underscores the indication that they might still be suitable habitats, given improved management for wildlife. Non-forested areas still provide ground cover and canopy shades for inhabiting wildlife species, thus, may likely to contribute to biodiversity in degraded peatlands of West Kalimantan, although may not as significantly as forested habi- tats. Similar results have also been reported, indicating that canal blocking contributes to habitat improvement. After 7.5 years of monitoring, a constructed dam in a peat swamp forest canal resulted in halved rates of peat surface subsidence and the spontaneous regrowth of 57 native tree species [90]. These findings suggest the importance of long-term obser- vation to fully understand the mechanisms by which canal blocking influences wildlife dynamics. It is also essential to statistically account for other interconnected factors, such as anthropogenic and climatic variables, as these are linked to wildlife community, species distribution and habitat use [91–93]. To enhance wildlife diversity in our study site, canal blocking alone is insufficient for rehabilitating degraded peatlands.

It represents just the initial step in an overall strategy aimed at reducing fire risk and supporting revegetation efforts [94,95]. We propose aligning biodiversity conservation efforts at the site with the natural climate solutions (NCS) hierarchy, which is part of nature-based solutions (NbS) and aims to reduce GHG emissions or enhance carbon sequestration while protecting biodiversity and human well-being [96]. NCS hierarchy begins with land protection and progresses to improve management and restoration [97]. In the NCS hierarchy, protection is the priority action, offering a large area of mitigation in a short time and being highly cost-effective with numerous co-benefits. The second action in the hierarchy is improved