Tropical Peat Forest Research Articles

SPATIAL VARIABILITY OF METHANE EMISSIONS FROM SOILS OF WET FORESTS: A BRIEF REVIEW

SPATIAL VARIABILITY OF METHANE EMISSIONS FROM SOILS OF WET FORESTS: A BRIEF REVIEW

Assessment of variability of peat physicochemical properties, subsidence and their interactions within Selangor forests

AbstractTropical peat swamp forests are carbon‐rich ecosystems both above‐ and belowground, which play a major role in the climate balance of the earth. The majority of the world's tropical peat forest cover is located in Southeast Asia and is increasingly threatened by anthropogenic disturbances. Despite their importance for biodiversity conservation and climatic balance of the earth, pristine peatlands are almost extinct in many parts of Southeast Asia. Peninsular Malaysia is one such region, where there are no undisturbed peatlands left in the west coast. We studied the largest peat forest area in the west coast of Malaysia, located in the state of Selangor. We evaluated variability of peat subsidence (for 1 year), peat physicochemical properties and macronutrient contents between forest regions and between different depths (not for subsidence) covering the top 50 cm, and the complex interactions between them. We found that there was significant peat subsidence in all the studied regions, however, there was no significant difference in subsidence between different forest regions. Physicochemical properties such as peat moisture, pH and carbon (C) content and all macronutrient contents except phosphorus (P), either varied between regions, or showed significant interactions between region and depth in Selangor peat forests. All the measured peat physicochemical properties varied with depth. Among macronutrients, only nitrogen (N), P and calcium (Ca) showed significant change with depth, while there were no changes with depth for sulphur (S), potassium (K) and magnesium (Mg) contents. These changes in each peat physicochemical property and macronutrient contents correlated with changes in other peat physicochemical properties and nutrient contents; however, there is a need for controlled experiments to further understand these significant interactions. The findings show continued carbon loss in secondary peat swamp forests through subsidence, indicating the long‐term impact of selective logging and associated historical drainage. The significant variability of peat physicochemical properties and macronutrient contents with region and depth, also show the need for intensive sampling to characterise large secondary peat swamp forests.

Agroforestry as Rehabilitation Strategy System in Orang Kayo Hitam Peat Swamp Park Forest, Jambi - Indonesia

Tropical peat forest ecosystems are unique and have multiple social, economic, and ecological benefits. Factors such as excessive drainage and frequent fires cause peatland degradation. Rehabilitation of deforested and drained tropical peat swamp forests is globally relevant in the context of deforestation and forest degradation. One management system that can be implemented in these conditions combines crops and forest plants (agroforestry). The challenges of the agroforestry application strategy in forest parks are the status of the land, which is a conservation area, and the characteristics of the surrounding community and field conditions. Based on these conditions, it is necessary to conduct this research to support the Orang Kayo Hitam (OKH) forest park development strategy appropriately. The research was conducted in May – June 2021 and used Force Field Analysis based on the opinions of 231 respondents. Based on the research results, it is known that respondents stated that the highest internal driving force is motivation to improve family’s economic from agroforestry products (score 52) and the external one is availability of endemic plants (score 45). The respondent’s opinion about the highest internal inhibiting factor is related to public knowledge of benefits from endemic plant species (score 39), while for external is related to market networks for Non Timber Forest Products (NTFP) market (score 43).

Carbon loss from a deforested and drained tropical peatland over four years as assessed from peat stratigraphy

Deforested, drained, and converted tropical peat forest is common in Southeast Asia, and these areas have become a major source of carbon (C) emissions. In this study, measurements of peat properties, i.e., peat thickness, organic matter (OM), bulk density (BD), total organic C (TOC), and total nitrogen (TN), were taken four years apart (2012–2016) at 24 sites in a previously deforested and drained tropical peat in West Kalimantan, Indonesia. We calculated that the average peat subsides at a rate of 3.8 ± 1.2 cm yr−1. The estimated net change in C stock ranged from −8 to −41 Mg C ha−1 yr−1, with an average of −31 Mg C ha−1 yr−1. C loss varied by peat depth and land use. C loss was four times faster on shallow peat (50–100 cm) than deep (>300 cm) peat sites. Fallow sites (bush fern and secondary forest) subsided and lost C faster than oil palm plantations, likely due to land-clearing fires. Percent C and C/N ratio declined significantly in the upper 150 cm of peat, especially in the fallow sites, indicating oxidation within the peat profile. No change occurred in bulk density, showing little effect of compaction, though the density profile migrated downward with subsidence. The current peat topography, modeled from satellite LiDAR data, reflects past peat-loss patterns and confirms the coring results. C loss in this region continues at a high rate since its original deforestation in the early 1970s. This study concludes that C loss due to anthropogenic disturbances on tropical peat is larger than the 2013 Tier 1-IPCC CO2 emission factor for Acacia and oil palms on drained tropical peats, which are 20 and 11 Mg CO2-eq ha−1 yr−1, respectively.

The Use of Subsidence to Estimate Carbon Loss from Deforested and Drained Tropical Peatlands in Indonesia

Drainage is a major means of the conversion of tropical peat forests into agriculture. Accordingly, drained peat becomes a large source of carbon. However, the amount of carbon (C) loss from drained peats is not simply measured. The current C loss estimate is usually based on a single proxy of the groundwater table, spatially and temporarily dynamic. The relation between groundwater table and C emission is commonly not linear because of the complex natures of heterotrophic carbon emission. Peatland drainage or lowering groundwater table provides plenty of oxygen into the upper layer of peat above the water table, where microbial activity becomes active. Consequently, lowering the water table escalates subsidence that causes physical changes of organic matter (OM) and carbon emission due to microbial oxidation. This paper reviews peat bulk density (BD), total organic carbon (TOC) content, and subsidence rate of tropical peat forest and drained peat. Data of BD, TOC, and subsidence were derived from published and unpublished sources. We found that BD is generally higher in the top surface layer in drained peat than in the undrained peat. TOC values in both drained and undrained are lower in the top and higher in the bottom layer. To estimate carbon emission from the top layer (0–50 cm) in drained peats, we use BD value 0.12 to 0.15 g cm−3, TOC value of 50%, and a 60% conservatively oxidative correction factor. The average peat subsidence is 3.9 cm yr−1. The range of subsidence rate per year is between 2 and 6 cm, which results in estimated emission between 30 and 90 t CO2e ha−1 yr−1. This estimate is comparable to those of other studies and Tier 1 emission factor of the 2013 IPCC GHG Inventory on Wetlands. We argue that subsidence is a practical approach to estimate carbon emission from drained tropical peat is more applicable than the use of groundwater table.

Carbon balance of tropical peat forests at different fire history and implications for carbon emissions.

Accurate assessment of tropical peat forest carbon stocks and impact of fires on carbon pools is required to determine the magnitude of emissions to the atmosphere and to support emissions reduction policies. We assessed total aboveground carbon (AGC) in biomass pools including trees, shrubs, deadwood, litter and char, and peat carbon to develop empirical estimates of peat swamp forest carbon stocks in response to fire and disturbance. In contrast to the common assumption that peat fires combust all AGC, we observed that about half of undisturbed forest AGC, equivalent to about 70Mg C ha-1, remains after one or two recent fires - mainly in dead trees, woody debris and pyrogenic carbon. Both recently burnt and repeatedly burnt peat forests store similar amounts of carbon in the top 10cm of peat when compared with undisturbed forests (70Mg C ha-1), mainly due to increased peat bulk density after fires that compensates for their lower peat C%. The proportion of fuel mass consumed in fire, or combustion factor (CF), is required to make accurate estimates of peat fire emissions for both AGC and peat carbon. This study estimated a CF for AGC (CFAGC) of 0.56, comparable to the default value of the Intergovernmental Panel on Climate Change (IPCC). This study estimated a varying CF for peat (CFPEAT) that ranged from 0.4 to 0.68 as depth of burn increased. This revised CFPEAT is one third to one half of the IPCC default value of 1.0. The current assumption of complete combustion of peat (CF=1.0) is widely acknowledged in the literature as oversimplification and is not supported by our field observations or data. This study provides novel empirical data to improve estimates of peat forests carbon stocks and emissions from tropical peat fires.

Identifying and addressing knowledge gaps for improving greenhouse gas emissions estimates from tropical peat forest fires

Tropical peatlands are areas of high carbon density that are important in biosphere-atmosphere interactions. Drainage and burning of tropical peatlands releases about 5% of global greenhouse gas (GHG) emissions, yet there is great uncertainty in these estimates. Our comprehensive literature review of parameters required to calculate GHG emissions from burnt peat forests, following the international guidelines, revealed many gaps in knowledge of carbon pools and few recent supporting studies. To improve future estimates of the total ecosystem carbon balance and peatfire emissions this study aimed to account for all carbon pools: aboveground, deadwood, pyrogenic carbon (PyC) and peat of single and repeatedly burnt peat forests. A further aim was to identify the minimum sampling intensity required to detect with 80% power significant differences in these carbon pools among long unburnt, recently burnt and repeatedly burnt peat swamp forests.About 90 Mg C ha−1 remains aboveground as deadwood after a single fire and half of this remains after a second fire. One fire produces 4.5 ± 0.6 Mg C ha−1 of PyC, with a second fire increasing this to 7.1 ± 0.8 Mg C ha−1. For peat swamp forests these aboveground carbon pools are rarely accounted in estimates of emissions following multiple fires, while PyC has not been included in the total peat carbon mass balance. Peat bulk density and peat carbon content change with fire frequency, yet these parameters often remain constant in the published emission estimates following a single and multiple fires. Our power analysis indicated that as few as 12 plots are required to detect meaningful differences between fire treatments for the major carbon pools. Further field studies directed at improving the parameters for calculating carbon balance of disturbed peat forest ecosystems are required to better constrain peatfire GHG emission estimates.

Impact of Land-Use Change on Soil Carbon Dynamics in Tropical Peatland, West Kalimantan- Indonesia

The conversion of tropical peat forest to other land uses can reduce organic carbon (C) and stable C isotope (δ13C) of peat soil. This research aimed at analyzing the soil organic-C and δ13C of peatland with respect to maturity (fibric, hemic and sapric) in five types of peatland use, which included primary peat forest, secondary peat forest, shrubs, oil palm plantations, and cornfield in West Kalimantan. Analysis of peat soil samples includes organic C with Loss in ignition method and δ13C using an isotope ratio mass spectrometry(IRMS) method. Organic-C at fibric was higher than hemic and sapric, respectively (57.2%, 57.0%, 56.4%), meanwhile, organic-C was the highest on primary peat forest, followed by on secondary peat forest, oil palm plantation, cornfield, and shrubs, respectively 57.1%, 57.0%, 56.4%, 56.0%. The cause of increasing and decreasing organic C and δ13C due to land-use change due to changes in vegetation, burning during tillage, and age of organic matter of peat soil. This condition causes the opening of natural peat ecosystems and changes in anaerobic to aerobic conditions.

The exchange of water and energy between a tropical peat forest and the atmosphere: Seasonal trends and comparison against other tropical rainforests

Tropical rainforests control the exchange of water and energy between the land surface and the atmosphere near the equator and thus play an important role in the global climate system. Measurements of latent (LE) and sensible heat exchange (H) have not been synthesized across global tropical rainforests to date, which can help place observations from individual tropical forests in a global context. We measured LE and H for four years in a tropical peat forest ecosystem in Sarawak, Malaysian Borneo using eddy covariance, and hypothesize that the study ecosystem will exhibit less seasonal variability in turbulent fluxes than other tropical ecosystems as soil water is not expected to be limiting in a tropical forested wetland. LE and H show little variability across seasons in the study ecosystem, with LE values on the order of 11 MJ m−2 day and H on the order of 3 MJ m−2 day−1. Annual evapotranspiration (ET) did not differ among years and averaged 1579 ± 47 mm year−1. LE exceeded characteristic values from other tropical rainforest ecosystems in the FLUXNET2015 database with the exception of GF-Guy near coastal French Guyana, which averaged 8–11 MJ m−2 day−1. The Bowen ratio (Bo) in tropical rainforests in the FLUXNET2015 database either exhibited little seasonal trend, one seasonal peak, or two peaks. Volumetric water content (VWC) and VPD explained a trivial amount of the variability of LE and Bo in some of the tropical rainforests including the study ecosystem, but were strong controls in others, suggesting differences in stomatal regulation and/or the partitioning between evaporation and transpiration. Results demonstrate important differences in the seasonal patterns in water and energy exchange across different tropical rainforest ecosystems that need to be understood to quantify how ongoing changes in tropical rainforest extent will impact the global climate system.

Eddy Covariance Measurements of Methane Flux at a Tropical Peat Forest in Sarawak, Malaysian Borneo

AbstractTropical biogenic sources are a likely cause of the recent increase in global atmospheric methane concentration. To improve our understanding of tropical methane sources, we used the eddy covariance technique to measure CH4 flux (FCH4) between a tropical peat forest ecosystem and the atmosphere in Malaysian Borneo over a 2‐month period during the wet season. Mean daily FCH4 during the measurement period, on the order of 0.024 g C‐CH4·m−2·day−1, was similar to eddy covariance FCH4 measurements from tropical rice agroecosystems and boreal fen ecosystems. A linear modeling analysis demonstrated that air temperature (Tair) was critical for modeling FCH4 before the water table breached the surface and that water table alone explained some 20% of observed FCH4 variability once standing water emerged. Future research should measure FCH4 on an annual basis from multiple tropical ecosystems to better constrain tropical biogenic methane sources.

Tropical Peat Swamp Management Options: A Case Study Using System Dynamic in Southern Aceh

Tropical peat forest ecosystems have multiple benefits as regulating hydrological system, carbon storage, timber and non-timber products, and protecting the biodiversity. Lack of understanding of these functions, short-term economic benefits is more preferable despite reducing its ecological benefits. This study proposed a system dynamics model of tropical peat forest ecosystem in determining its optimum management for extractive utilizations (timber and non-timber forest products), environmental services, and biodiversity. A dynamics model was used to describe changes in peatland and forest cover, biomass accumulation and carbon storage, and total economic value of tropical peat forest ecosystem in Trumon and Singkil, Southern Aceh. The projection showed that peat forest ecosystem benefits would decline in the long term if degradations continue at the same rate over last decade. Efforts to change the primary peat forest to plantation would reduce the total economic value of ecosystem and biodiversity values at level -19.63% and -26.28% from current conditions. Carbon emissions were increased at 117.32 tons CO2 eq ha-1 year-1, higher than average of carbon losses from peatland oxidation. Preserving 50% of forest vegetation on moderate depth and protection very deep peatlands would reduce emission -6.96% to -35.06% and increase forest carbon storage at significant rate +15.06% to +63.32%, respectively. These mitigation schemes would improve the biodiversity and hydrological function. Forest rehabilitation with agroforestry practices will enhance carbon uptake, especially on degraded lands.

Origin, composition, and transformation of dissolved organic matter in tropical peatlands

Solid and dissolved organic matter (DOM) compositions were investigated in a pristine and a deforested tropical peat forest in Brunei Darussalam. A combination of elemental (%C, %N, C/N), isotopic (δ15N, δ13C, Δ14C), molecular (lignin phenol biomarkers) and optical (Specific UV Absorbance at 280nm (SUVA280), fluorescence index (FI)) analyses were performed to characterize DOM in porewater and river water. The DOM composition was compared to vegetation and peat to assess DOM origin and transformations in the ecosystem. Significant relationships were observed between optical properties (SUVA280, FI) and bulk (Δ14C) and molecular (ratio of cinnamyl to vanillyl phenols, C/V) composition of DOM.The radiocarbon content of DOM shows that it is modern at both sites for both surface and deep (to 4.5m) samples (Δ14C=74.58±8.53‰ at the pristine site and Δ14C=87.84±4.5‰ at the deforested site for the first 2 meters), indicating transport of young DOM to deeper layers. Stable carbon-13 content of vegetation, peat and DOM showed only slight fractionation and ranged from −32.2‰ to −28.3‰. Nitrogen showed a greater shift between ecosystem pools. Nitrogen-15 content was higher in the solid peat (δ15N=−0.92±0.49‰ in the pristine site, δ15N=−1.22±1.37‰ in the deforested site) than in DOM (δ15N=−4.2±2.5‰ in the pristine site, δ15N=−4.1±2.3‰ in the deforested site). This difference in δ15N is significantly correlated with the C/N values of peat and DOM and attributable to higher microbial degradation in the peat compared to DOM. Porewater DOM contains less lignin (λ8=1.10±0.27mg100mgdw−1 in the pristine site and λ8=1.38±0.46mg100mgdw−1 in the deforested site) than does the solid peat (λ8=5.66±2.14mg100mgdw−1 in the pristine site and λ8=10.29±4.69mg100mgdw−1 in the deforested site). All indicators of lignin degradation (P/(V+S), 3,5Bd/V, (Ad/Al)V, (Ad/Al)S) are significantly higher in DOM than in the solid peat. This shows that lignin can be processed rapidly in the porewater of upper layers of tropical peatlands.Logging activity affected the composition of organic matter at the deforested site. Higher lignin content (λ8) was observed in the solid peat, and the composition of DOM differed greatly in the deforested site: Δ14C, FI, 3,5Bd/V, (Ad/Al)V are significantly different from the pristine site. Thus it appears that the composition of DOM is more sensitive than the solid phase to the effects of land use change on organic matter dynamic in tropical peatlands.

Estimation of Total Carbon Stocks in Soil and Vegetation of Tropical Peat Forest in Indonesia

The study was conducted in the forest concession area of PT. Diamond Raya Timber, Riau Province, Indonesia. Measurement and calculation carbon stocks in soil and vegetation of tropical peat forest should be done accurately to anticipate carbon trading. The objective of the study is to estimate carbon stocks in soil and vegetation in 4 forest conditions. The study found that biomass and carbon stocks in the soil was 8 times higher than in the vegetation in primary forest condition, and 10 times in logged over forest and secondary forest condition. Carbon stocks in vegetation and soil were 189.45 ton C ha -1 and 1537.37 ton C ha -1 in primary forest, 161.76 ton C ha -1 , and 1713.77 ton C ha -1 in logged over area, 139.05 ton C ha -1 and 1486.39 ton C ha -1 in secondary forest, and 43.09 ton C ha -1 and 1205.59 ton C ha -1 in degraded forest. Allocation of carbon stocks in the standing trees in primary forest, logged over area, secondary forest, and degraded forest were 70, 60, 62, and 7% respectively.

Impact of peat-fire disturbance to forest structure in tropical peat forest in Central Kalimantan, Indonesia

Impact of peat-fire disturbance to forest structure in tropical peat forest in Central Kalimantan, Indonesia

Growth-Promoting Properties of Bacteria Isolated from Rhizosphere and Rhizoplane of Dipterocarp Plants on Acidic Lowland Tropical Peat Forest in Central Kalimantan, Indonesia

Growth-Promoting Properties of Bacteria Isolated from Rhizosphere and Rhizoplane of Dipterocarp Plants on Acidic Lowland Tropical Peat Forest in Central Kalimantan, Indonesia