The potential biomass, carbon stock and CO2 sequestration of forest litters at Sibolangit nature park

Several factors generated CO2 releasing into the atmosphere in large quantities and persist. The CO2 concentration is continuously increase (exceeding 400 ppm in 2019) leading to more negative impact of global warming and climate change. Biomass is a key parameter in estimating and predicting ecosystem productivity, carbon storage, nutrient sharing, and fuel accumulation in assessing an ecosystem. This study aims to analyze the biomass, carbon stock and carbon sequestration of forest litters at Sibolangit nature park. The research data was recorded at Sibolangit Tourism Park, located in Sibolangit, Deli Serdang, North Sumatera. 0.5 m x 0.5 m plot was placed based on the simple random sampling method to collect the litters. The 5% sampling intensity was applied resulting in total of 30 sampling plots. All litter in the sample plots was collected and weighed to determine the wet weight. 100 grams of sample was then placed in a sample plastic and labelled. The litter biomass was calculated using the formula according to SNI7724-2011. This research calculated the biomass, carbon stock, and carbon sequestration of litter at Sibolangit nature park, i.e., 86.92 ton ha−1, 40.85 ton ha−1, and 149.94 ton ha−1. The results support the role of Sibolangit nature park in climate change mitigation by reduction of carbon emission.


Introduction
Several factors generated CO 2 releasing into the atmosphere in large quantities and persist [1].The CO2 concentration is continuously increase (exceeding 400 ppm in 2019) leading to more negative impact of global warming and climate change [2].A sustainably managed forest is naturally the most effective carbon absorber storing approximately 48% of carbon [3,4].Biomass is the total weight or volume of organisms in a certain area.Biomass is also defined as the total amount of living matter above the surface of a tree and is expressed in tons of dry weight per unit area [5].Biomass is a key parameter in estimating and predicting ecosystem productivity, carbon storage, nutrient sharing, and fuel accumulation in assessing an ecosystem [6.7].Forest absorbs and stores the CO2 in the carbon pools, i.e., all parts of above-ground vegetations, roots, deadwoods, soils, and litters [8,9].
Litter is the top layer of forest soil in the form of plant parts that have died and have not undergone the decomposition process such as fallen leaves, twigs, branches, flowers, fruit, bark, and other parts [10,11].Forest ecosystem, which is the greatest carbon sink on earth, transfers the net primary production to the soil through litter biomass decomposes.Changes in the litter carbon pool, as a result, have significant consequences for global carbon emission reduction targets.According to the Indonesian government regulation No. 28/2011, Nature Park (TWA) is a nature conservation area that utilize mainly to nature tourism and recreation.Sibolangit nature park (TWA Sibolangit) was established in 1980 based on Minister of Agriculture Decree No. 636/Kpts/Um/1980 covering 24.85 Ha of conservation area located at Sibolangit, Deli Serdang, North Sumatera.This study aims to analyze the biomass, carbon stock and carbon sequestration of forest litters at Sibolangit nature park.

Materials and methods
The research data was recorded at Sibolangit Tourism Park, located in Sibolangit, Deli Serdang, North Sumatera.0.5 m x 0.5 m plot was placed based on the simple random sampling method to collect the litters.The 5% sampling intensity was applied resulting in total of 30 sampling plots [12].All litter in the sample plots was collected and weighed to determine the wet weight.Approximately 100 grams of sample was then placed in a sample plastic and labelled.The litter biomass was calculated using the formula according to SNI7724-2011 [13].

Result and discussion
The results showed that the higher litter biomass was found at plot 1, 9 and 2 with the value of 10.84 ton ha -1 , 7.93 ton ha -1 , and 5.90 ton ha -1 , respectively (Figure 2).The litter was generated from vegetation composing the area.Swietenia mahagoni, Lansium domesticum, and Pinus merkusii were the dominant species at these three plots.S. mahagoni was identified with 40 cm DBH and 3.9 m height, L. domesticum was 94 cm DBH and 4.9 m height, whereas P. merkusii was 67 cm DBH and 3.9 m height.P. merkusii was the dominant tree species at Sibolangit Nature Park (2 nd highest IVI) [14].This species also dominated Salib Kasih forest area with the seed available throughout the year indicating great adaptation and regeneration ability [15].Pinus spp. was one of the major tree species in Japan's forest that sinks carbon in the range of 0.67-62.5 ton ha -1 [16].The total litter biomass at the research site was 86.92 ton ha -1 .The value was higher than litter biomass at two undisturbed forest sites of southeast Bartin province [17].
The amount of biomass potential is influenced by the ability of plants to absorb carbon from the atmosphere through the process of photosynthesis.Carbon is stored in the tree stem, roots, above ground (litter) and in the soil (humus) [18].It is well-known that forest litter plays the important role in the forest ecosystem.It serves as a primary supply of organic matter, protects the soil from the extreme climate fluctuation, and prevents the soil erosion [19].The litter carbon biomass content in each plot varies depending on its constituent components, such as rotted wood, leaves and twigs.Physical and chemical factors are also influence the amount of carbon litter biomass in the certain ecosystem.The litter carbon stock and sequestration at research site was varied ranging from 0.66 ton ha -1 to 10.84 ton ha -1 (Figure 3).Similar to the litter biomass, the highest carbon stock and sequestration was recorded at plot 1, i.e., 5.09 ton ha -1 and 18.69 ton ha -1 , respectively.In addition, the other plots with higher value were plot 9 and 2, with the carbon stock of 3.73 ton ha -1 and 2.77 ton ha -1 , and the carbon sequestration of 13.68 ton ha -1 and 10.17 ton ha -1 .
The amount of carbon stored is closely related to the biomass.The ability of a vegetation to store biomass describes the condition of carbon stores in a forest area.Carbon is a fraction of CO2 absorbed by forest vegetation through the process of photosynthesis which is then stored into biomass.The total of carbon storage is directly proportional to the biomass [20].Previous research found that the carbon stock was mostly recorded to be in the forest litter and soil, which was 59% [21].The litters at Sibolangit nature park stored approximately 40.85 ton ha -1 carbon with the sequestration of 149.94 ton ha -1 .It was higher than the carbon stock in litters of Bangladesh's Tankawati natural hill forest (4.21 ton ha -1 ) [21], Ethiopia's Tara Gedam forest (0.90 ton ha -1 ) [22] and conterminous United States (CONUS)'s forest land (10.45 ton ha -1 ) [23].Carbon sequestration is the process when CO2 from the atmosphere or other emission sources is stored in the oceans, terrestrial environments (vegetation, soil, sediments), and in rock formations.Forest biomass is very relevant to the issue of climate change that plays an important role in biogeochemical cycles, especially in the carbon cycle.Of the total forest carbon, around 50% is stored in forest vegetation.As a consequence, forest destruction, fires, and logging will increase the carbon emission to the atmosphere [24].
Several efforts to increase the carbon sequestration are: enhancing the natural growth of forest biomass, supplying more wood reserves by planting more trees, and reforesting the abandoned land with fast growing tree species [8].The results support the role of Sibolangit nature park in climate change mitigation by reduction of carbon emission (Figure 4).The term of mitigation refers to efforts addressing the main drivers of climate change, i.e., by reducing greenhouse gas pollution [25].Sustainable management need to be applied at Sibolangit nature park to preserve the forest and its role as the carbon pool.

Conclusions
This research calculated the biomass, carbon stock, and carbon sequestration of forest litter at Sibolangit nature park, i.e., 86.92 ton ha -1 , 40.85 ton ha -1 and 149.94 ton ha -1 .

Figure 1 .
Figure 1.Map of research location and sampling points.

Figure 2 .
Figure 2. Litter biomass distribution and dominant vegetation at research plots.

Figure 3 .
Figure 3. Distribution of forest litter carbon stock and CO2 sequestration at research plots.