Predicting forest fire danger using fuel characteristics in Berbak Sembilang National Park

Analyzing the fuel characteristics of a forest is essential when creating fire danger rating system (FDRS) and understanding how forest fires behave. In this study, the researchers predicted the intensity of forest fires by examining the amount of fuel present Berbak and Sembilang Natinal Park between November 2020 and December 2021. The fuel load measurement was carried out on surface fuel in the burned peatland area by modifying the line-intersect method (triangular plot - Van Wanger 1982) and the method developed during the Kalimantan Forest Climate Project (KFCP). We assessed the possibility of forest fires occurring, based on the fuel conditions. Variations were found in the fuel quantity and composition on the forest’s surface layer across different regions. Consequently, the intensity and type of forest fires changed accordingly. The Berbak Sembilang National Park area proved more intense surface fires. These results underscore the importance of understanding regional fuel characteristics and analyzing the predicted intensity and type of forest fires to take timely preventive measures against early fire occurrences.


Introduction
Forest fires are caused by interaction of fuel, oxygen, and heat, and their shape and intensity depend on weather, topography, and fuel [1].Understanding fuel characteristics in the forests is crucial for modelling fire behavior and managing wildfires [2].Over the years, biomass accumulation in forest increased significantly.This increase in biomass and older trees creates a more vulnerable forest structure with higher fuel continuity, increased fuel loads per hectare, denser understory vegetation, and greater amounts of fallen branches, leaf litter, and decaying wood, making the forests prone to large wildfires.Vegetation-based fuel classification alone cannot fully explain all fire characteristics, as different vegetation types can exhibit similar fire behaviors.Additionally, correlating plant classifications with fuel properties poses challenges.To address these issues, previous research has measured fuel loadings of surface and canopy fuels within forests and classified forest fuels based on the fire characteristics observed with different fuel types.This approach better represents actual fuels in forests and enables the prediction of fire intensity.
To overcome this limitation, this study analyzed fuel loads in Berbak Sembilang National Park, including litter layers, duff layers, fallen branches, understory vegetation, trees, and shrubs, expressed as fuel load per unit area (kg/m2).The study focused on Berbak and Sembilang National Park, which has experienced the most significant fire damage over the past year.The observation locations in this study were chosen within Berbak Sembilang National Park area, passing through 11 buffer villages Air Hitam Laut Village, Parit 10, Air Hitam Laut Parit 7 Village, Sungai Palas Village, Simpang Datuk Village, Sungai Jeruk Village, Sungai Cemara Village, Remau Baku Tuo Village, Sungai Rambut Village, Telago Limo Village, Sungai Benuh Village, and Labuan Pering Village.Berbak Sembilang National Park is situated in the wetland region spanning the provinces of Jambi and South Sumatra on the eastern part of Sumatra Island.The park's geological formation primarily consists of alluvial deposits, encompassing fine materials such as clay and sand.The area exhibits three predominant physiographic types: alluvial plains, peat swamps, and tidal areas.These areas are characterized by regular flooding, low-lying landscapes, and extensive peat swamp regions.The park is intersected by important rivers, particularly the Eastern River originating from the Bukit Barisan Mountains, which form expansive river estuaries with mudflats, eventually flowing into the Malacca Strait and the South China Sea.The eastern part of the park, situated in low-lying terrain, has continuously experienced sediment influx from the rivers throughout the Holocene period.The alluvial plains in this area are still expanding steadily towards the east, with an estimated annual land accretion rate of 20 meters.However, it is important to note that Jambi lacks available data due to the dynamic nature of its coastal areas, where some regions may undergo erosion instead of land addition.In certain areas, erosion rates can reach up to 20 meters per year.So, the fuel characteristics and environmental factors within these areas were analyzed to evaluate fire occurrence and fire risk based on fire intensity.Forest fire prediction and spread systems consider meteorological, fuel, and topographical factors, with forest fuel playing a crucial role in triggering large-scale wildfires.Understanding the characteristics of forest fuel is essential for predicting and managing wildfires.Therefore, this study aimed to analyze the characteristics of forest fuel in Berbak Sembilang National Park to gain insights into fire behavior and provide fundamental data for the development of prediction and spread systems.

Research Metodology
The survey was conducted from 2019 to 2020.As shown in Fig. 2, 10 m × 10 m quadrats were installed within the survey area.Within each quadrat, the locations of all woody plants and their diameter at breast height (cm), height (m), underground height (m), were recorded.Additionally, within the 10 m × 10 m quadrats, three 1 m × 1 m quadrats were installed in the bottom left, center, and top right corners.Samples of woody debris and litter, smaller than 6 cm in diameter, were collected from these quadrats and measured for dry weight (kg) before and after drying.Three 10 cm × 10 cm quadrats were placed within each 1 m × 1 m quadrat in the bottom left, center, and top right corners to measure the depth (cm) and dry weight (kg) of the litter layer and humus layer.This survey methodology aligns with the commonly used approach for assessing fuel characteristics within forests in the United States [3].

Analysis of Forest Fuel Characteristics 2.3.1. Fuel load.
The fuel load measurement was carried out on surface fuel in the burned peatland area by modifying the line-intersect method (triangular plot -Van Wanger 1982) and the method developed during the Kalimantan Forest Climate Project (KFCP) [4] using the quadratic method or rectangular plot to sample large fuels (> 7.5 cm).The diameter of each fuel type (dead or dry branches, roots, twigs, etc.) intersecting the rectangular plot was measured.Medium-sized fuels (2.5-7.5 cm) were measured using the same method, while small fuels were measured using 1 m × 1 m plots on the peat surface.All small fuels were cut and stored in large plastic bags to be weighed and dried in an oven until they reached a constant weight.2.3.2.Heavy Fuel Load.Heavy fuel refers to woody fuel with a diameter greater than 7.5 cm located above the ground surface.The field method used to determine the quality and quantity of large fuel involves preparing a thin rope with a minimum length of 120 m, a GPS device, and measuring tape.A rectangular plot is then established, and measurements are taken for all materials within and adjacent to the plot.The diameter of the materials is measured using a measuring tape.In addition to recording the diameter of the materials within the plot, it is important to note whether the material is a tree trunk, tree branch, stump, or root, and whether the material emerges from within the peat or is simply lying on top of it.2.3.3.Medium Fuel Load.Medium fuel load refers to wood materials with diameters between 2.5 cm and 7.5 cm that emerge from within the peat or lie on the peat surface.The field method employed to determine the quantity and quality of medium-sized fuel involves using a line-intersect plot, which is based on the rectangular plot used for assessing large fuel.The process begins with placing the plot positions, using a different colored rope, and then extending a thin rope for a distance of 10 meters along the intersection between Point 1 and Point 2. The materials within this segment are examined and measured using a measuring tape.The quantity and quality of fine fuel, on the other hand, refer to vegetation materials with diameters < 2.5 cm.These are measured within small squares connected to the triangular intersection plot (Figure 2), which is constructed to estimate the amount of heavy (large) fuel load.2.3.4.Fine Fuel Load.A small plot measuring 1 m x 1 m is used to estimate the fine fuel load in units of tons per hectare.The procedure involves preparing a PVC pipe with a diameter of 2 cm and cutting it into segments of 4 m x 1 m.These segments are then connected to form a square using PVC angle joints or "knees."The angled joint sections are not glued to allow for easy disassembly and relocation to the next location.On each side of the rectangular plot between Point 1 and Point 2, with a distance of 30 m (Figure 2), at a point 15 m from Point 1, a 1 m segment is measured at a 90-degree angle.g in tons per hectare.The collected samples in bags are placed on a tarp and evenly mixed.Then, the samples are weighed to obtain the net weight by calibrating the scale until it reaches a constant weight.The samples are then placed back into bags to obtain the oven-dry weight and recorded.Oven dry the samples at 85 °C for 24 hours.Afterward, individually remove each sample, reweigh until a constant weight is achieved.

Result and Discussions Table 1 Total Biomass of 11 Study Sites
Table 1 summarizes the characteristics of each study site.Among the study sites, Parit 10 had the highest density of surface fuels (408.86 ton/ha) and Pematang Raman had the lowest (280.76 ton/ha).According to [5] when the surface fuel moisture content is higher than the threshold for crown fire initiation, rapid spread of the fire can lead to the occurrence of passive crown fires.Allowing for the change in weather factors within the study area, if the spread rate of the fire increases rapidly, crown fires are likely to develop.In this study, observations were made regarding the characteristics of surface fuel load, which includes the proportion of dead and live fuels, the proportion of leaves and branches, and the moisture content of the fuel.The study locations were within the TNBS (Taman Nasional Bukit Sumatera) area, which encompassed 11 surrounding villages, including Air Hitam Laut Parit 10 Village, Air Hitam Laut Parit 7 Village, Sungai Palas Village, Simpang Datuk Village, Sungai Jeruk Village, Sungai Cemara Village, Remau Baku Tuo Village, Sungai Rambut Village, Telago Limo Village, Sungai Benuh Village, and Labuan Pering Village.The effect of fuel moisture on fire behavior is to slow down the rate of combustion or fuel consumption.The presence of larger fuel loads serves as an indicator of previous fire occurrences [6].The composition of large fuel loads consists of cellulose (41-53%), hemicellulose (15-25%), and lignin (16-33%), which results in higher severity levels compared to moderate fuel loads dominated by cellulose and hemicellulose with a smaller lignin component.Therefore, as wood decays, the relative proportion of lignin in the remaining biomass may increase by up to 65% [7].Fuels with high chemical compound and volatile compound content possess high energy content, making them more prone to easy combustion.The large fuel load primarily consists of large dead trees and fallen debris from the fire event in 2015.
Fuel moisture content, which refers to the mass of water present within the fuel, is crucial in determining the combustibility of a fuel.Fuel moisture content is widely used in fire hazard assessments and predictive systems.The cellular structure of plants contains empty spaces that hold water, which plays a role in photosynthesis and cellular metabolism.Water also provides structural support for living plants.The cellular structure is preserved in leaf litter and branches, which make up the dead and decaying fuel.This results in dead fuel having pores that allow for water absorption, similar to the process of diffusion, which governs adsorption and desorption.Weather factors also greatly influence the amount of water contained in the fuel, such as temperature, humidity, and rainfall.Under constant temperature and relative humidity, dead fuel particles eventually reach equilibrium moisture content (EMC), which is a function of the immediate environmental conditions surrounding the fuel particles.The time required for fuel particles, especially wood stems, to reach equilibrium with their surroundings increases with increasing diameter.2 also shows that fine fuel load in had a higher surface fuel intensity.This can be attributed to the greater spread rate of the fire.According to research, even with a higher fuel load, if the spread rate is slow, the fire intensity remains low.Fine fuels can quickly respond to changes in moisture and relative temperature.Fuels of this size often become the primary carriers of forest fires following changes in weather variables.Relative humidity is also crucial in determining fuel moisture content as it determines the moisture gradient between the air and fuel particles.With increasing air temperature, both live and dead fuel moisture content will decrease.Plants have their own mechanisms for regulating water supply from the soil and air and releasing water into the atmosphere.Many of these mechanisms are specifically designed to conserve water.Climate conditions, particularly humidity and relative temperature, have influenced the level of water requirements for plants.The average availability of heavy fuel was 725.63 tons/ha at each fuel sampling location.Field observations show that the majority of large fuels in TNBS consist of fallen wood stems resulting from previous fires.Previous fires in TNBS have caused changes in land cover.Partial canopy opening in TNBS reduces the area's capacity and the underlying peat deposits to maintain moisture.Climate change at the micro and regional levels, including decreased relative humidity, increased temperature, and wind speed [8;9;10], coupled with human disturbances such as illegal logging in TNBS, can make tropical forest fuels more susceptible to ignition.Changes occurring in TNBS have made the available fuels more vulnerable to fire, and at the same time, weather conditions and other disturbances can modify fire behavior, resulting in higher availability of fuels and higher fire severity levels [11].

No
There is a reciprocal relationship between disturbances to the TNBS area and the availability of fuel and forest fires.The disturbances occurring in the area are believed to have a connection that contributes to climate change in the wet tropics.The frequency and intensity of drought are the most significant climate changes associated with fuel availability.Climate change consists of the effects of increased greenhouse gas emissions, aerosol loading, and land cover changes in drought-prone regions [11].

Conclusion
The fuel characteristics of forest fuels were measured to analyze the intensity and form of wildfires and assess regional wildfire risk.From 2019 to December 2021, the forest fuels in 11 locations in Berbak Sembilang National Park.The measured fuel characteristics included tree spacing, tree diameter at breast height, underground biomass, tree height, tree species, leaf litter and duff thickness and weight, and fallen branches.Wildfire intensity increases with higher fuel accumulation in the forest, highlighting the importance of managing forest fuel loads in regulating wildfire risk.Although higher forest fuel accumulation generally leads to higher wildfire intensity.Berbak Sembilang National Park area proved more intense surface fires.These results underscore the importance of understanding regional fuel characteristics and analyzing the predicted intensity and type of forest fires to take timely preventive measures against early fire occurrences.

Figure 1 .
Figure 1.The location of study

Figure 2 .
Figure 2. Forest Fuel Acquisition scheme.Point 1 is used to collect heavy fuel.Point 2 is used to collect small fuel.

Figure 3 .
Figure 3. Fuel Structure on site

Table 2
The Amount of Fuel Load in Each Study Site Table