Anju Subedi1, Dipika Badal1, Ram Asheshwar Mandal2* and Bijay Kumar Yadab3
Received: August 28, 2020; Published: September 09, 2020
Corresponding author: Ram Asheshwar Mandal, School of Environmental Science and Management (SchEMS), Kathmandu, Nepal
Carbon stock and biodiversity have an intricate relationship. Despite the important relationship between these components the studies related to it are very limited. Thus, this research was objectively conducted to estimate species wise carbon stock, soil organic carbon and biodiversity. Three community forests namely Sungure, Goraksha and Baghkhor of Dang district were selected for the study. Total 45 nested sample plots having 12.61m, 5.64m, 2.82m and 1.87m radius for tree, pole, sapling and seedling respectively were established to collect the data. Additionally, 45 soil samples were collected from 0-10, 10-20 and 20-30 cm depth from centre of the plot. The diameter and height and tree species were recorded. The biomass of each species was calculated using equation Chave  and the value was converted into carbon. Soil carbon was analyzed using Wakley and Black method. The biodiversity was estimated using Shannon Weinner and Simpson’s Diversity Index. Shorea robusta was the dominant species in the community forests, thus the carbon stock was the highest around (mean±SE) 33.23±0.23, 28.15±0.25 and 20.61±0.65 ton/ ha in Baghkhor, Goraksha and Sungure community forests respectively. The carbon stock of Shorea robusta was 38.61 to 41.31% which can suppress other species. One-way ANOVA and Tukey’s b test showed that the mean carbon stock of Shorea robusta in the community forests was significantly differed at 95% confidence level. The highest contribution of carbon stock was of soil around 64.77 (57.52%) ton/ha in Baghkhor community forest. The soil carbon stock of Baghkhor community forest was 26.65, 21.55, 16.57 ton/ha at 0-10 cm, 10-20 cm, 20-30 cm respectively. The species richness was the highest 17 in Sungure community forest. The Simpson index was 0.32, 0.34 and 0.34 in Sungure, Goraksha and Baghkhor community forests respectively while Shannon- Weiner diversity index values were 1.31, 1.13 and 1.3 in the community forests respectively. The research will be useful to understand the carbon stock and biodiversity in community forest.
Keywords: Carbon, volume, biodiversity, importance value index
The carbon sequestration has been playing a vital role to
mitigate and adapt against the climate change. In fact, the forest
is sink and source of carbon as well. On the other hand, the forest
is the source of biodiversity too. So, conserving the forest means
conserving the forest carbon as well as biodiversity. However, the
inverse process is also true. About 20 % greenhouse gases can be
cut conserving the forest [2,3]. Importantly, conserving the forest is
able to address the issues of climate change as well as biodiversity.
The united national framework convention on climate change and
convention on biodiversity highly emphasize on the conservation
of the forest [4-6].
Carbon sequestration is the process of removing additional carbon from the atmosphere and depositing it in other reservoir principally through change in land use . Mainly, two mechanisms have been working to incentivize to credit the carbon stock in the forest . The Reducing Emission from Deforestation and Degradation (REDD+) and Clean Development Mechanism (CDM) . The REDD+ mechanism also value the biodiversity but considers this as the co-benefit, though biodiversity is equally important in the world [10,11]. Thus forest conservation is one of important element of REDD+ mechanism. Developing countries are assumed as foundation of REDD+ mechanism and implementation of convention of biological diversity.
Developing countries are committed to work under the REDD+ mechanism and to work for convention on biological diversity . In fact over 80 countries have been working under the forest carbon partnership facility under the REDD+ mechanism [13,14]. Besides, total 196 countries are the member of convention on biological diversity [15,16]. Both mechanisms need to build the database and update regularly. Community managed forests functioning to upscale the carbon sequestration as well as the biodiversity. In this context, parties need the reliable information regarding forest carbon and biodiversity. This can be done through intensive studies. Community forests are famous management approach in the world to assure the increasing carbon stock but the biodiversity conservation is questionable. The examples of community forest management for carbon sequestration and biodiversity of Cost Arica, Papua New Guinea, Mexico, and India including Nepal are evidence.
Community forests, collaborative forest, leasehold forest, buffer zone forest are decent ground of carbon sequestration and biodiversity conservation in Nepal [17,18]. There are over 23,000 community forests, more than 70 buffer zone community forests, 23 collaborative forests in Nepal. All these forests are potential for forest carbon credit. However, biodiversity conservation in the community forest especially where the management practices are intensively applied is in doubt. This research tried to evaluate the carbon stock of tree species in the community forests, soil carbon and biodiversity as well.
Three community forests namely Sungure, Goraksha and Baghkhor community forest of Dang district, Nepal were selected as the study area. Dang is the largest valley of Nepal and Asia. It lies in Province no. 5. The forest area of this district is 192,155 ha around 65% of total land area. It ranges between 28°30’.00’ʹ N and 82°18’.00’ʹ E. Sungure community forest lies in Ghorahi sub metropolitan 18, covering 84.64 ha. Goraksha community forest lies in Ghorahi sub metropolitan city 18, Dabari, covering 81.89 ha and Baghkhor community forest lies in Ghorahi sub metropolitan city 16, Bahundadha, covering 82.91 ha. The Shorea robusta, Terminalia tomentosa, Dalbergia sisso and Acacia catechu are the most common tree species in the community forests (Figure 1).
Stratified random sampling was applied based on the stage of the tree to collect the data. The forest areas was surveyed and mapped. Next, total 45 sample plots 15 plots in each community forest were distributed randomly on the map. Total nested sample plots of 12.61m, 5.64m, 2.82m and 1.87m radius for tree, pole, sapling and seedling respectively were established in the field to collect the data .
The diameter at breast height, height and tree species were recorded. Additionally, 45 soil samples were collected from 0-10, 10-20 and 20-30cm depth from the center. Then sapling (5cm< dbh >1cm), seedlings were counted and fresh weights were noted.
All collected data were analyzed quantitatively. The biomass
was calculated using equation of Chave . AGTB = 0.0509* ρ D2H,
where AGTB = Above-Ground Tree Biomass (kg); ρ = wood specific
gravity (kgm-3); D = tree diameter at breast height (cm) and H =tree
height (m). The Above Ground Sampling Biomass (AGSB) (kg) was
calculated using formula; Ln (AGSP) = a +b ln (DBH); Ln is natural
log, a & b are constants. D is the diameter at breast height (cm)
[20,21]. The Below Ground Biomass (BGB) was calculated using
root shoot conversion factor 0.125 . Besides, the fresh weight
was taken of regeneration (sapling and seedling) and dried in
the lab to find the dry weight. The unitary method was applied to
determine the biomass of regeneration. The carbon stock density
of soil organic carbon was calculated using Walkley and Black 
SOC = ρ × d × %C, where SOC = soil organic carbon stock per unit area [t/ ha], ρ (Bulk Density g/cc) = (oven dry weight of soil)/ (volume of soil in the core), d = the total depth at which the sample was taken [cm], and %C = carbon concentration [%].
Finally the carbon stock was calculated where conversion factor used was 0.47 on biomass of total pools except soil carbon.
Total carbon = C (AGTB) + C (AGSB) + C (BGB) + C (LHG) + SOC
Where, C (AGTB) = carbon in aboveground tree biomass [Mg C /ha]; AGTB*0.47
C (AGSB) = carbon in aboveground sapling biomass [Mg /ha]; AGSB * 0.47
C (BGB) = carbon in below ground biomass [Mg C /ha]; BGB * 0.47
C (LHG) = carbon in litter, herbs, and grasses [Mg C/ha]; LHG*0.47
SOC = soil organic carbon [Mg C/ha]
For calculation of Biodiversity Index, the species diversity of the forest tree community was calculated using different indices as mentioned below:
Simpson’s diversity index (D) =i2, where pi is the total individuals in a species community,
Shannon-Weiner Biodiversity Index (H`) = -ΣPi*Log Pi, where Pi = ni / N, where, N=Total no of species, ni= no. of individuals of species and Pi= ni/N
Normality test was done to check the normality of the data set. The data were normal thus one way ANOVA test and Tukey’s b test was applied to evaluate whether soil carbon was significantly differed among the community forests.
The carbon stock was varied according to species in the community forests. Shorea robusta was the dominant species in the community forests, thus the carbon stock was the highest around (mean±SE) 33.23±0.23, 28.15±0.25 and 20.61±0.65 ton/ha in Baghkhor, Goraksha and Sungure community forests respectively. The estimated carbon stock was followed by Terminalia alata with 10.76±0.37, 10.32±0.34 and 6.93±0.3 in Baghkhor, Goraksha and Sungure community forests respectively. The proportion of carbon stock of Shorea robusta was 38.61 to 41.31% which can suppress other species to regenerate and growth as this is a valuable timber species, users have no interest to promote other species in the community forest (Table 1). One-way ANOVA and Tukey’s b test showed that the mean carbon stock of carbon of Shorea robusta in these community forests at 95% confidence level since the p-value was less than 0.05. Similar condition was found of carbon stock of Terminalia alata but Tukey’s be showed that the mean carbon stock was of Goraksha and Baghkhor community forest was significantly differed from Sungure community forest at 95% confidence level.
Table 1:Species wise carbon stocks.
Note: The word in parenthesis is local name of the tree species.
The highest contribution of carbon stock was of soil around 64.77 (57.52%) in Baghkhor community forest. Maximum soil carbon was 50.40 % in Sungure community forest. The contribution of tree carbon stock ranges from 23.24, 33.06 and 34.27 ton/ha which were around 26.01, 26.87 and 25.14% of total carbon in the community forests (Table 2). The soil carbon stock was also compared based on the depth layers in each community forest. It was found that the soil carbon stock of Baghkhor community forest was found to be highest in three layers (0-10 cm, 10-20 cm, 20- 30 cm) with values, 26.65, 21.55, 16.57 ton/ha respectively than that of other community forest i.e. Goraksha community forest having value 26.30, 17.38, 14.57 ton/ha and Sungure community forest having value 18.97, 14.20, 11.85ton/ha in three layers (0-10 cm, 10-20 cm, 20-30 cm) respectively (Table 3). One way ANOVA showed that, there was a significant difference in soil carbon in different community forest and similar result was found applying the Tukey’s b test at 95% confidence level.
Species richness: The species richness was the highest 17 in Sungure community forest which was 15 in Goraksha community forest and only 12 tree species in Baghkhor community forest. Total 17 plant species were found in Sungure community forest, out of which about 13 plant species were common in all three selected forests. Shorea robusta, Melaleuca leptospermum (Maluku), Dalbargia sissoo, Terminalia alata , Garuga pinnata (dabdabe), Eugelharlia spicata (Mahuwa), Mallotus philippensis (Rohini), Syzygium cumini (Jamun), Aesandra butyracea (Churie), Anthocephalus chinensis (Kadam), Trichilia connoaroides (Aakha tarya), Phyllanthus emblica (Amala), Pyracantha crenulata (Dhayro), Pterocarpus santalinus (Kattai), Rhus wallichii (Bhalayo), Acacia catechu (khair) and Dillenia pentagyna (Tantari).
Simpson’s diversity index value and Shannon- Weiner diversity index: The Simpson index was 0.32, 0.34 and 0.34 in Sungure, Goraksha and Baghkhor community forests respectively while the Shannon- Weiner diversity index values were 1.31, 1.13 and 1.3 in the community forests respectively (Table 4). Statistically, ANOVA test also showed that there was no difference in values of Simpson’s index and Shannon-Wiener index among three community forests at 5% level of significance.
The study of total carbon stocks in three selected community forest found that the estimated total per ha biomass carbon of Sungure, Goraksha and Baghkhor community forest was 44.32, 64.78 and 71.52ton respectively. Based on comparison of species in the community forest it was found that, the estimated carbon stock of Shorea robusta was highest, having value of 33.23±0.23 ton/ha in Baghkhor community forest, 28.15±0.25 ton/ha in Goraksha community forest and 20.61±0.65 ton/ha in Sungure community forest. Mandal  showed that the carbon stock of Shorea robusta was nearly 52.31ton/ha, which is slightly higher than the present study. The main reason of highest carbon stock of Shorea robusta was because of the dominancy of this species in the community forests.
Based on report published by department of research and survey, estimated tree carbon (>10cm) was 104.47 ton/ha which is slightly higher than present study as the present study. This may be due to the potential of forest to sequester carbon depends on the forest type, age of forest and size of trees [25-27]. The density of carbon stock values would vary according to the geographical location, plant species, age of the stand, aboveground input received from leaf litter, decomposition of fine roots below ground, management practices and other operating ecological factors [28- 30].
Khanal  estimated that the above ground tree carbon was 40.02 ton/ha and the above ground tree carbon of Sungure, Goraksha and Baghkhor community forest is found to be 44.32, 64.78 and 71.52 ton/ha which is slightly higher than the report presented by Khanal . Similarly, the study done by KC showed that the value of above ground carbon of Shorea robusta in Jhilbang community forest of Pyuthan was 82.54 ton/ha which is slightly higher than the present study. The above ground carbon variation in age of the stand ranged from 18-75 years, variation in carbon per hectare from 34.70-97.86 ton/ ha . Moreover, Shrestha  estimated carbon stocks in trees showed that 219 ± 34 Mg ha–1. Shrestha assessed the net above ground carbon stock in six community forests of the Dolakha district, Nepal where it was found that the community forests accumulates approximately 117.44 tons of carbon in total.
Based on the report of department of forest research and
survey (DFRS), the soil organic carbon of Terai was estimated as
33.66 ton/ha and the soil organic carbon found from the present
study is 64.77, 58.26 and 45.04 ton/ha which is slightly higher
than the DFRS report. Ghimire  reported that the soil organic
carbon of Makawanpur district is 58.82 ton/ha. Mandal 
reported soil organic carbon in Chyandanda community forest
of Mahottari district is 58.22 ton/ha which is slightly higher
than Sungure community forest having value and lower than
Baghkhor community forest but approximately similar to Goraksha
community forest. The study done by Pandey and Bhusal 
showed that soil organic carbon of Terai community forest was 95.1
ton/ha which is higher than the present study.
The soil organic carbon of this study shows that the carbon content decreased with the increase in soil depth in three forest areas. The total soil carbon stock in depth 0-10 cm contained greater value than in depth 10-20 cm and followed by 20-30cm respectively. This may be because of the higher aggregate of humus in the top layer of the soil profile in the forest blocks, decreased content of organic matter with the increased level of soil depth and also due to soil organic carbon diminishing with the depth regardless of vegetation, soil texture and clay size fraction [36,37]. The decrease in soil carbon with the increase in soil depth was supported by the following studies. The study conducted by Sharma  in Shree Salumbudevi community forest of Pukhulachhi VDC, Kathmandu, which showed the maximum amount of the soil organic carbon was obtained in the upper layer 0-10 cm as compared with the lower layer 20-30 cm. The comparative reports and the present study thus shows that the amount of soil carbon decreases with increasing soil depth in the studied community forest.
The Simpson’s and Shannon’s indices of Sungure, Goraksha and Baghkhor community forest were found to be 0.32, 0.34, 0.34 and 1.31, 1.13, 1.3 respectively. Lower the Simpson’s index value higher the diversity and higher the Shannon’s index value higher the diversity. The biodiversity indices values were slightly differed between the forests. The study done by Mandal, showed that the Shannon-Wiener Biodiversity Index was the highest 2.33 in Banke- Maraha collaborative forest (CFM), and it was the lowest 2.21 in Gadhanta-Bardibas CFM. Similarly, the Simpson index values were 0.39, 0.41 and 0.44 in Banke-Maraha. Tuteshwarnath and Gadhanta-Bardibas CFM respectively, this was not similar to the value of community forest because of the application of silviculture operation done in our study areas. The silviculture operation reduce the biodiversity [39-70].
The dominant species was Shorea robusta in the community forest, thus the carbon stock was the highest of this species. The carbon stock contribution was about similar proportion of biomass and soil. The soil carbon decreased with the increased soil depth. Simpson’s diversity index and Shannon-Wiener index values showed that, the plant species diversity was not significantly different in three community forests. The study also recommended that the assessment of biomass carbon stocks and biodiversity of community forest should be given priority to include in operational plan of community forest.
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