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 15 / 23 management, which provides a lower-cost mitigation potential than restoration and requires minimal or no changes in land use. Restoration is third in the hierarchy because it is less cost-effective and requires land-use changes. Restoration NCS aim to rehabilitate or reestablish forest, wetland, and grassland ecosystems in areas where these habitats once naturally existed. This strategy is necessary for areas experiencing severe loss and degradation. Although the NCS hierarchy out- lines a defined order, in practice, protection, improved management, and restoration can work together to achieve optimal results. Understanding the characteristics and needs of each habitat is crucial for choosing the appropriate NCS hierarchy strategy. The NCS hierarchy outlines a defined order, in practice, protection, improved management, and restoration can work together to achieve optimal results. Understanding the characteristics and needs of each habitat is crucial for choos- ing the appropriate NCS hierarchy strategy. Our survey in the less disturbed peat forest within the Kubu Raya Landscape indicates that the forest has not yet reached climax in its ecological development and is still in the process of succession, dominated by trees with diam- eters of up to 20 meters. The peat forest that is still regenerating had canopy heights of 12–18 m while the canopy of mature forest can reach up to more than 45 m [98]. Since the less disturbed peat forest in the Kubu Raya Landscape

has the potential to regenerate naturally, the primary management priority is to protect the area from further distur- bance. This practice has indeed been applied in the area for approximately 10 years. In the past, the forest was a target for illegal logging, but after the area was designated as protected forest by the Permata Village Government, people rarely visited, and extractive activities fully ceased. The protection regulations have helped the forest recover from past disturbances and offer an ideal habitat for wildlife. The condition of the less disturbed peat forests in Kubu Raya, which have been locally protected for the past 10 years, demonstrates that if protection is applied by halting illegal logging, the forests can grow, support higher plant diversity, and serve as habitats for endangered plant spe- cies. [99]. The disturbed peat forest in the Mempawah Landscape exhibits a similar stage of ecological succession to the less disturbed forest in Kubu Raya, as both are still undergoing natural succession. However, ongoing disturbances con- tinue to impact the forest in the Mempawah area. The most recorded undergrowth vegetation we found in disturbed peat forests of Mempawah is alike to that found colonized disturbed wet shrubs and estate crops. These species are typical pioneer, wind-dispersed fern species [100]. These are not usually found in mature peat forest but become abun- dant after disturbances such as land clearing and burning [100,101]. However, the presence of other abundant under-

story species (herb and woody lianas), trees, and canals only at the edge of the forest, suggests that disturbances have occurred some time ago and there have been no recent massive disturbances in disturbed peat forests [102]. These indications were confirmed during conversations with local people during our surveys. They stated that the forest is now under the management of the local forestry agency, with the primary concerns being forest fires, illegal wildlife hunting, and selective logging of certain tree species that have reached a certain age (usually the sapling stage) or a diameter of less than 10 cm. During our surveys, we neither observed nor heard of any actions regarding the replanting of vegetation due to legal restrictions imposed on disturbed forest areas, suggesting that any vegetation growth occurs naturally. Protection is the NCS strategies also needed by the disturbed peat forest, as these forests have the potential to regen- erate naturally and only require support to boost recovery. Research has shown that a peat forest in Central Kalimantan that experienced a single burning event in 1997 demonstrated similar Shannon diversity and plant species counts to unburned forests after 13 years [99]. Similarly, research from Central Kalimantan also demonstrates that peat forests sub- jected to selective logging in the past have a strong natural regeneration potential, shown by their high resemblance to rel- atively undisturbed forests in terms of tree density, species richness, and a similar understory vegetation community [103].

Additionally, if illegal hunting is curtailed, the forest could benefit from the presence of mammals and birds, which would serve as seed dispersers and pollinators to aid in the regeneration process [104]. Despite instances of illegal activity such as burn-clearing, logging, and hunting, disturbed peat forests in Mempawah Landscape still hold promise as potential