Carbon Sequestration in the Trees of Community Forest: A Case Study of Hasantar Community Forest, Kathmandu, Nepal

Carbon sequestration is one of the main ecosystem services in today’s condition. Estimation of above ground tree biomass and carbon stock is important as it gives ecological and economic benefits to the local people. This study was conducted in the Hasantar Community Forest (HCF) of Nagarjun Municipality, Kathmandu. Concentric circular plots of 12.62m radius were established in five different blocks of HCF for the study of tree species. The main objective of this study was to find out the Important Value Index (IVI), Above Ground Tree Biomass (AGTB) and carbon stocks tree species of HCF. This forest comprises the tree species of families like fagacaeae, moraceae, myrtaceae, fabaceae etc in dominant numbers. Schima wallichii was found ecologically most significant tree species as it possess highest IVI value. The carbon stock of this plant was found as 206.865 t/ha which comprises 27 % of total carbon in HCF. The total above ground tree carbon stock of HCF (55.4 ha.) was found 144.795 t/ha.


Introduction
Community forestry is a participatory forest management system in Nepal that was started in the late 1970s. Glimour and Fisher (1991) defined community forestry as the control, protection and management of forest resources by rural communities for whom trees and forests are an integral part of their farming system. According to Forest Act 1993, community forest is a part or parts of National forest area handed over to a user groups for its development, conservation and utilization for collective benefit of the community. It is an institutional innovation of empowering local communities in managing forest resources for their benefit in co-ordination with government. According to the official website of MOFSC/ DoF/ GoN 2018, 18 th February, about 1.45 million households or 35 percent of the population of Nepal is involved in community forestry management program. Hasantar community forest is located in ward no. 7 of Nagarjun municipality, Kathmandu. It was established in 2051 according to the Forest Act 2049. It lies about 3.5 Km north from Kalanki, Kathmandu. It covers 55.4 hectors land area.
Carbon sequestration refers to efforts to capture excess carbon dioxide from the atmosphere, condense it and store it in some benign way (Kirschbaum, 2003). Carbon sequestration is the removal of the CO2 from the atmosphere Case Study R.S. Gautam (2019) Int. J. Appl. Sci. Biotechnol. Vol 7(1): 124-129 This paper can be downloaded online at http://ijasbt.org&http://nepjol.info/index.php/IJASBT by storing it in the biosphere. Carbon is one of the essential elements of life and green plants have unique ability to assimilate it in the form of carbon dioxide as raw material for food preparation (Jain, 1983). Thus forest plays a key role in climate change, both sinks and sources of CO2 (Shrestha et al., 2016a). A forest is natural sinks for CO2 and plays a significant role in sequestrating the atmospheric carbon into biomass and soil. It helps to reduce the concentration of greenhouse gases in atmosphere. The natural sinks of carbon include forest and soil (IPCC, 2000). Compared to other terrestrial ecosystem forests store the most carbon (Pan et al., 2011). The potential for carbon sequestration is quite high for mitigating the effects of global warming. It is known that the amount of carbon in the soils of terrestrial ecosystem is approximately three times that of atmosphere. The amount of carbon is also 700 times more than the estimated annual increase of carbon dioxide in the atmosphere. The terrestrial ecosystem are a huge natural biological scrubber for the CO2 from the various sources. Carbon sequestration in terrestrial ecosystem can occur in living aboveground biomass. For effective carbon sequestration, the increased photosynthetic carbon fixation must occur in long lived pools. Trees take up CO2 during photosynthesis plants can store carbon in above ground and below ground parts for longer period of time. It is estimated that 10 to 15 % of the excess carbon dioxide in the atmosphere can be removed by creating large tree plantation (Singh et al., 2006). There is considerable variation in the above-ground carbon stock and rate of carbon sequestration according to forest types and its geographical location. Forests representing the Terai region of Nepal had high above-ground carbon stock per hectare compared to hilly region. However, carbon sequestration rate of forest types depended on growing nature of the forest stands. Tropical riverine, Pine and Alnus nepalensis forests are important for carbon sequestration in tree biomass in Nepal, as seen from the comparatively higher carbon accumulation rates (Baral et al., 2009).

Materials and Method
This Hasantar Community Forest (HCF) is divided into five blocks for the easy management and protection of forest. According to Hasantar Community Forest User Group (HCFUG), this forest is in pole stage where maximum plants have diameter 10cm to 29.9 cm. It is north-west facing natural forest where Katush, Gurans, Chilaune, Utish, Pinus, Setikath, Kafal etc are dominant tree species. The primary data was collected from field visit and forest survey. Diameter at breast height (DBH), height of the tree, number of tree species, and number of sapling were recorded in the field. For the measurement of the height of tree Clinometer was used. Longitude and latitude, altitude, slope of the land were also recorded by using GPS, Altimeter and Compass during the field visit. The forest is subtropical type. The dominant tree species are Schima wallichiana, Alnus nepalensis, Pyrus pashia, Prunus cerasoides, Myrica esculantum, Alnus nepalensis, Rhododendron arboreum etc. The five number of concentric circular sample plots of size 500m 2 and radius 12.62 m were established for the estimation of carbon stock. The primary data collected in the field was used in the calculation of the various vegetation parameters viz. relative density, relative frequency and relative basal area by using the formulas. The ecological value of a tree species of the community forest was calculated by adding Relative Frequency, Relative Density and Relative Basal Area.
Above ground tree biomass (AGTB) of the forest was calculated by the allometric equation developed by Chave et al. (2005) (m) The AGTB of all trees of the sample plot was summed up and it was divided by the area of sample plots (500m 2 ) which determined biomass stock density in Kg/m 2 . This value of biomass stock density converted to t/ha by multiplying it by 10. The biomass stock of a sampling plot was converted to carbon stock after multiplication with the default value of carbon fraction 0.47 suggested by Ban Carbon Mapan Margadarsan, 2071 BS.

Forest Characters
Hasantar Community Forest consists of total thirty one types of tree species of nineteen different families. Fagaceae and Moraceae have maximum number of species i.e four species in each. Families like Meliaceae, Pinaceae, Juglandaceae etc have one species in this forest. Family Fagaceae and Moraceae covers about 25.8% of trees species in the forest. (Fig.1  According to this study, the forest of HCF was found Schima-Rhododendron type of subtropical forest. (Fig; 2).

DBH Class of the Trees
The largest number of tree species in HCF was found in 21-30 cm DBH class. 31% of total trees were found in the DBH class 21-30 cm and only 1% of the trees were in DBH class <61 cm. (Fig. 3)

Biomass Stock Density
Biomass represents the potential amount of carbon that could be added to the atmosphere as carbondioxide when the forest is cleared and burned. Biomass stock density estimation provides the means for calculating the amount of carbondioxide that could be removed from the atmosphere by vegetation. In HCF biomass stock density of Schima wallichii is found highest i.e. 81.722 t/ha. Biomass stock density of five dominant species of HCF is 187.811 t/ha. (Fig. 4)

Carbon Content in Different Tree Species
Carbon content in different species of trees was found different since their frequency, density, DBH (diameter at breast height) and height were different. Schima wallichii has highest carbon stock value and Gaultheria fragrantissima has lowest carbon stock value. (Fig. 5).

Discussion
Altogether thirty-one tree species of nineteen families and twenty-five genuses have been identified in HCF.  (Jati, 2012). Similarly, Shrestha et al. (2016b) have been found that Schima wallichii of subtropical forest has highest carbon sequestrating rate than other trees. This study also found that Schima walichii has highest carbon sequestrating rate in HCF. The carbon stock value of trees in HCF is found lesser than the Alnus nepalensis forest where carbon stock was found 186.05 t/ha (Ranabhat et al, 2008).

Conclusion
This study provides current estimation of forest tree above ground biomass and carbon stock in the Hasantar Community Forest at Nagarjun Municipality Kathmandu. The common tree species of HCF are found as Schima wallichii, Rhododendron arboreum, Myrica esculenta etc. According to the vegetation parameters Schima wallichii was most dominant and ecologically significant tree species. The forest is found in pole stage according to their DBH value. The average above ground biomass of five dominant species is 187.811 t/ha and the average above ground carbon stock is found 144.795 t/ha.

Acknowledgement
The author express special thanks to the office of Dean, Institute of Science and Technology Tribhuvan University for providing funding for this research and the author is also grateful to Patan Multiple Campus, botany department for providing all the necessary equipment for this research.