Peat Physical and Hydraulic Properties Due to Peatland Fires

Fires on tropical peatlands in Indonesia are unexpected events that happened sporadically, especially during dry seasons. It is not easy to judge why a fire presents in a certain spot, and how it spreads. There are indications, and originally, a fire is ignited intentionally to clear bushes and wood remnants on the land surface for land clearing. Its most negative impacts are on human health due to dispersing smokes locally, and occasionally, reached neighboring countries. It is not unusual, the fire spread beyond the initial spot, and burned a vast area of commercial plantations, and protected forests in the vicinity. Fires caused significant economic losses. This investigation aimed at making clearer how peat properties changed before and sometime after the fires burned the areas. We observed how fires in peatlands occurred, and to what extent the physical properties of peats altered due to fires. Observations were carried out in 4 locations within Riau province, South Sumatra province, and South Kalimantan province that have vast areas of peatlands in the country, and peatland fires there are more frequent. The observations focused on peatland morphological appearances, and physical properties of non-burned and after fires in protected forests, plantations, and smallholder lands. The physical and hydraulic properties that were analyzed, among others, are bulk density, particle density, porosity, available water capacity, and water permeability. Positive changes were experienced successively by the air-entry head (21.3%) followed by permeability (19.6%), particle density (15.9%), bulk density (10.7%), available water (7.4%), fast-drain pore (3.9%) and n-parameter (0.1%). While, negative changes were experienced successively by slow-drain pore (-72.2%), residual water content (-22.5%), porosity (-7.3%), saturated water content (-6.3%) and m-parameter (-2.6%). The increase of air-entry head and the available water indicated more capable of retaining more water. Meanwhile, the increase of permeability and fast pore drain mean the burnt peats would be easier to drain under the same suction gradient. However, based on the F-test with a probability value of 5%, those all changes were not so significant or considerably small compared to the associated critical values.