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 16 / 23 habitats, and, if left to regenerate naturally with interventions focused on illegal activities protection, they can progress into more mature forests with high biodiversity [105]. In estate crops where peatland has already been converted to oil palm plantations, the NCS hierarchy to support biodiversity conservation and increase carbon sequestration includes protection and improved management. Since the vegetation complexity of estate crops cannot provide suitable habitats for a wide range of wildlife species, protection from hunting—which still occurs in these areas—is crucial to maintain existing biodiversity. Hunting, especially targeting rare and endangered species, needs to be minimized as much as possible, as some wildlife have large area coverage, which is a consequence of establishing a plantation in a previously forested area [106]. Moreover, according to our results, one factor that supports estate crops as wildlife habitats is the presence of understory vegetation. The plantation management protocols in oil palm plantation, such as undergrowth clearing for fruit harvesting, road development, pest and weed man- agement, or tillage, can potentially eliminate understory coverage, impacting the biodiversity of the estate crop [107–109]. Maintaining understory coverage in estate crops can be considered an improved management practice. The presence of understory plants does not compete with oil palms; instead, it provides multiple benefits, such as reducing CO₂ emis-

sions, increasing carbon stocks, enhancing biodiversity, improving water and soil nutrient balances, and reducing erosion [110,111]. Furthermore, replacing the homogeneous structure with heterogeneity in oil palm plantations can enhance habitat quality to sustain forest-like areas [112]. Oil palm plantations in peatland areas are well-known actors in the cascading effects of habitat quality degradation, one of which is biodiversity loss. In addition, plantations can harbour species, usu- ally common species, which are sometimes considered pests and potentially invasive and in long-term could increase the wild crop-raiding population thus affecting the forest [113]. The estate is also not being used by forest-specific species as habitat, especially those that are peat forest specialists [109]. Adopting the jangka benah strategy—a solution to address unauthorized oil palm plantations in forest areas by implementing oil palm agroforestry—could be a suitable practice for estate crops to diversify vegetation [114]. Rather than expanding land area, intensification within existing areas will likely increase yield and optimize biodiversity conservation [115]. Participation in oil palm certifications (roundtable on sustainable palm oil (RSPO) or Indonesian sustainable palm oil (ISPO) by companies or smallholders is another form of improved management that can help prevent biodiversity loss, with recent reports indicating positive impacts of these certifications on biodiversity [116].

The disturbed wet shrub areas in the Mempawah Landscape, which are dominated by open areas, require more inten- sive recovery actions. For disturbed wet shrublands already used for agriculture, improved management practices need to be applied. An agroforestry system that enriches the land with woody plants offers an alternative for farmers to increase yield potential while contributing to biodiversity conservation and climate change mitigation. In addition to agricultural use, some disturbed wet shrub areas are left open. For these areas, protection should be prioritized, as fire regimes pose one of the greatest threats to dry peatlands, especially since canals have disrupted their hydrological systems [15,117]. In disturbed wet shrub areas that experience recurring fires, the third level of NCS, which is restoration, is the only way to recover the area. Repeated burning proved to prevent regeneration [101]. Studies show that a single forest fire can transform an initially forested area into an open area, but regeneration can occur relatively quickly due to the fire’s facilitation of seed sprouting for some species [99,100]. However, recurring fires can deplete soil nutrients, reduce soil fertility, diminish canopy, and ground cover, eliminate vegetation roots, and ultimately halt the process of plant regrowth and seed sprouting, resetting the succession to level zero [101,118,119] This chain reaction can significantly decrease biodiversity levels and increase the

dominance of specific plants, such as herbaceous ferns, in an area. This condition aligns with the observation results drawn from disturbed wet shrub [120]. With the worsening effects of rising global temperatures and El Niño periods, there is a drive to improve attitudes and strengthen restoration projects like never before [15,121,122]. Repeated fires are one of the factors halting open peatland revegetation. It is crucial to consider this when conducting restoration in vast peat wet shrublands.