Suria Darma Tarigan

Introduction: Deforestation and fires have caused substantial loss of tropical peat swamp forests (PSF) in Southeast Asia. Substantial efforts have been undertaken to rewet and revegetate peatlands, but these restoration measures can lead to conflicting outcomes. Knowledge is needed on how to combine revegetation and rewetting approaches to effectively restore peatlands. Objectives: Using a large‐scale field manipulation in Sumatra, Indonesia, on a former Acacia plantation on peat, the effects of water table depth (WTD) below the peat surface and shading conditions on planted tree species were tested. Methods: WTD was manipulated through surface treatments by lowering the peat surface to differing depths (0, −0.25, and −0.50 m) and carried out shading manipulation across 72 plots with a complementary natural Acacia tree shading experiment in 12 plots. Individual tree survival and growth of 3124 seedlings from 16 species were monitored from 24 up to 36 months, alongside natural regeneration. Results: Higher water tables with prolonged inundation inhibited seedling growth, survival, and natural regeneration. Full shade treatment with artificial netting increased seedling survival but reduced growth during the first 12 months. Similar effects were observed in the natural Acacia tree shading experiment. There were significant species differences in response to treatments and continuous WTD variation. Conclusions: Our findings showcase that too much rewetting has the potential to negatively influence planted seedling growth and survival and highlight the importance of shading to ensure seedling survival. These insights provide a foundation for defining optimal WTD targets and species selection strategies for PSF restoration.

Soil moisture and the groundwater tables are important for the sustainable management and maintenance of tropical peatland ecosystems. This study examined the long-term impacts of fires and logging on groundwater tables and soil moisture in peatlands used for Acacia plantations. Four land conditions were compared: natural forest (FRS), unharvested Acacia plantations (UHV), post-harvest areas in 2016 (HV), and post-fire areas in 2015 (BAR). Observations were made during the rainy and dry seasons to determine how peat responded to rainfall. The soil conditions observed included groundwater levels measured by the gravimetric method and dipwells, and other soil properties such as bulk density, soil porosity, and water-filled pore space. The results showed that natural forest and unharvested Acacia sites experienced increased soil moisture content during the wet season and a shallower groundwater table than the burned area, which consistently recorded the lowest values. All sites experienced a dramatic decline in both groundwater table and soil moisture during the dry season. This decline was most severe in post-fire peatlands, where the groundwater table fell by more than 80 cm and soil moisture declined from 389% to 230% in some locations. Statistical tests confirmed that both burning and logging had a significant effect on the physical characteristics of peat and groundwater table (? = 0.05). This study shows that, after many years, burned and harvested peatlands continue to experience hydrological degradation and are unable to maintain stable groundwater tables and soil moisture.

Using oil palm empty fruit bunches (EFB) as an organic amendment is a crucial strategy to improve soil quality in oil palm plantations, particularly on nutrient-poor Spodosol soils. This study aimed to evaluate the effects of 2 EFB application methods (incorporation into the soil and surface mulching) on soil organic carbon (SOC), nitrogen content, earthworm populations as soil biological indicators of fertility, and oil palm performance. A 12-month field experiment was conducted with observations every 4 months, using a completely randomized design (CRD) with 3 treatments and 9 replications each (n = 27 experimental units). The treatments included no EFB application (T0), EFB incorporated into the soil (T1), and EFB applied as surface mulch (T2). The results showed that both EFB application methods significantly increased SOC compared to the control, with the highest SOC observed in T2 (2.30±0.34%) after 12 months. Earthworm populations also increased progressively, reaching 19.33 individuals m-2 in T2. Pearson correlation analysis revealed a strong positive relationship between SOC content and earthworm abundance (r = 0.60; p < 0.001). These results confirm that EFB application, especially through surface mulching, is an effective and sustainable approach to enhancing soil quality, biological activity, and ecosystem functioning on Spodosols in oil palm plantations.

Rapid land use and land cover (LULC) changes in densely populated watersheds pose serious challenges to the sustainability of ecosystem services (ES), yet their spatially explicit economic consequences remain insufficiently understood. This study analyzes the spatio-temporal dynamics of LULC and ecosystem service values (ESVs) in the Citarum Watershed, Indonesia, one of the country’s most critical and intensively transformed watersheds. Multi-temporal Landsat imagery from 2003, 2013, and 2023 was classified using a Random Forest algorithm, while future LULC conditions for 2043 were projected using a Multi-layer Perceptron–Markov Chain (MLP–MC) model under three scenarios: Business-as-Usual (BAU), Protecting Paddy Field (PPF), and Protecting Forest Area (PFA). ESVs were quantified at multiple spatial scales (county, 250 m grids, and 100 m grids) using both the Traditional Benefit Transfer (TBT) method and a Spatial Benefit Transfer (SBT) approach that integrates biophysical indicators with socio-economic variables. The contribution of LULC transitions to ESV dynamics was further assessed using the Ecosystem Service Change Intensity (ESCI) index. The results reveal substantial historical forest and shrubland losses, alongside rapid expansion of settlements and dryland agriculture, indicating intensifying anthropogenic pressure on watershed functions. Scenario analysis shows continued degradation under BAU, limited mitigation under PPF, and improved forest retention under PFA; although settlement expansion persists across all scenarios. Total ESV declined from USD 2641.33 million in 2003 to USD 1585.01 million in 2023, representing a cumulative loss of 46.13%. Projections indicate severe ESV losses under BAU and PPF by 2043, while PFA substantially reduces, but does not eliminate economic degradation. ESCI results identify forest and shrubland conversion to settlements and dryland agriculture as the dominant drivers of ESV decline. These findings demonstrate that integrating multi-scenario LULC modeling with spatially explicit ESV assessment provides a more robust basis for ecosystem-based spatial planning and supports sustainable watershed management under increasing development pressure.

Bulukumba Regency, located along the Walanae Fault and within a seismic gap zone, indicates the potential for future earthquake recurrence. However, the regional and community capacity to address earthquake hazards remains weak, as evidenced by the lack of regulations accommodating earthquake studies in Bulukumba. This study aimed to design an earthquake mitigation model based on a stakeholder approach in Bulukumba Regency. The methodology employed MACTOR (Matrix of Alternatives for Choice and Trade-Offs), utilizing survey and questionnaire data. The output is a framework for policymakers in earthquake mitigation activities. The results suggested two effective alternative models: (i) a stakeholder formulation model based on role capacity and (ii) a time segmentation model for stakeholder involvement in earthquake mitigation. Based on these two models, it is essential to establish strong coordination and collaboration among these actors in order to minimize the impact of disasters on both the community and the environment.

One significant approach to restore the ecosystem function of degraded peatlands is natural restoration. This study evaluated the effect of short-term natural restoration on groundwater table in several peatland conditions in the Acacia plantation retired since 2016. Four types of land: burned land, Acacia post-harvest land, retired Acacia plantation forest, and the natural forest were considered as our study area. This study analyzed soil properties and remote sensing using the NDVI index to evaluate vegetation density in 2016, 2019, and 2022. This study found that natural restoration in the period of 2016-2022 increased vegetation density, almost similar to natural forest vegetation. Both soil properties and groundwater table on Acacia plantation forest and natural forest were not significantly different. High saturated hydraulic conductivity and low bulk density on both areas supported the stability of peat hydrology. In addition, variations in rainfall affected the pattern of changes in groundwater table, with a decrease during the dry season and an increase during the rainy season. The findings of this study confirm that short-term natural restoration can restore hydrological and vegetation functions in degraded peatlands, especially in Acacia plantation areas. These findings can be scientific recommendations for sustainable peatland management.

Peatland fires are a significant environmental issue, impacting local ecosystems and contributing to global climate change. This study evaluates the Peat Fire Vulnerability Index (PFVI) for sapric and hemic maturity levels under oil palm plantations in Pangkalan Pisang Village, Riau Province. Data on groundwater level, soil moisture, rainfall, and maximum temperature were collected from December 2021 to December 2022. The PFVI, modified from the Keetch-Byram Drought Index (KBDI), was calculated and correlated with these variables. The groundwater level varied from 3 cm to 76 cm below the surface, with an average of 36.23 cm. In sapric blocks, 29% of the groundwater level was less than 40 cm, while 73% were deeper. In hemic blocks, 44% were less than 40 cm, and 56% were deeper. Soil moisture in the top 10 cm layer fluctuated between 32% and 55% (v/v) Results showed significant negative correlations between PFVI and groundwater levels (r = -0.173 to -0.889) and soil moisture (r = -0.835 to -0.808), indicating that lower groundwater levels and soil moisture increase fire risk. High PFVI values in July corresponded with the lowest rainfall (59 mm) and groundwater levels below 40 cm. The study highlights the importance of monitoring hydrometeorological conditions and soil properties to effectively predict and mitigate peatland fires. Our findings are crucial for developing strategies to manage peatland sustainability and reduce fire hazards, especially in tropical regions with prevalent oil palm cultivation.

Peatlands are crucial yet vulnerable carbon stores. Here, we investigated carbon biogeochemical processes in tropical peatlands converted to plantations. We measured carbon dioxide (CO ₂ ) and methane (CH ₄ ) concentrations, stable isotope ratios and radiocarbon content in an experimental Acacia crassicarpa plantation in Sumatra, Indonesia. We found exceptionally high levels of dissolved organic carbon (DOC), CO ₂ , and CH ₄ in porewater and drainage networks, indicating that Acacia plantations are carbon hotspots due to their high productivity and exposed carbon‐dense substrates. Stable isotope models revealed that while CO ₂ and CH ₄ are produced belowground, CH ₄ contribution was lower than in natural undrained peatlands. Radiocarbon analysis suggested that remobilized carbon contributed to the carbon pool, with a median age of ∼470 years before present. These findings constrain the links between land‐use, water table levels, and carbon dynamics, with implications for carbon management in plantation peatlands.

Palm oil is being criticized as an unsustainable product by the EU due to its association with deforestation and high carbon emissions. However, the producers in Indonesia do not acknowledge the criticisms. Therefore, this study aimed to compare the carbon footprint of a representative EU-produced vegetable oil, rapeseed oil, with Indonesian palm oil. The analysis is divided into two stages, namely (a) land use conversion (LUC) as well as (b) plantation and oil processing. LUC entailed the conversion of native vegetation, such as forest areas and grassland, to vegetable oil crops. The carbon opportunity cost was used to account for the LUC contribution to the carbon footprint. For plantation and oil processing stages, the LCA SIMAPRO was adopted. The results showed that when vegetable oil replaced high-carbon-storage vegetation such as forests, the LUC carbon footprint of rapeseed oil and palm oil production were 2.09 and 1.49 t CO₂eq t⁻¹ oil, respectively. Replacing low-carbon-storage vegetation, namely shrub/grassland, led to 0.05 and −0.43 t CO₂eq t⁻¹ of repressed and palm oils, respectively. Based on the LCA SIMAPRO, the carbon footprints of plantation and oil processing stages were 1.05 and 0.88 t CO₂eq t⁻¹ oil for rapeseed and palm oils, respectively. The cultivation of oil palm in peatland generated a higher total carbon footprint (i.e., combined LUC and plantation and oil processing stages) than rapeseed oil (13.8 to 3.14 t CO₂eq t⁻¹ oil). However, in non-peatland areas, the total carbon footprint of palm oil was lower than rapeseed oil (2.37 to 3.14 t CO₂eq t⁻¹ oil) when replacing tropical forest and temperate forest vegetation, respectively. The total footprint was 1.2 to 0.45 t CO₂eq t⁻¹ oil when both replaced shrub/grassland. The higher productivity of oil palm and lower fertilizer requirement contributed primarily to the lower carbon footprint in non-peatland areas.