L.Supriya Devi?P.S.Yadava

Carbon stock and rate of carbon sequestration in Dipterocarpus forests of Manipur,Northeast India

L.Supriya Devi1?P.S.Yadava1

We examined the carbon stock and rate of carbon sequestration in a tropical deciduous forest dominated by Dipterocarpus tuberculatus in Manipur, North East India.Estimation of aboveground biomass was determined by harvest method and multiplied with density of tree species.The aboveground biomass was between 18.27–21.922 t ha-1and the carbon stock ranged from 9.13 to 10.96 t C ha-1across forest stands.Aboveground biomass and carbon stock increased with the increase in tree girth.The rate of carbon sequestration varied from 1.4722 to 4.64136 t ha-1year-1among the dominant tree species in forest stands in tropical deciduous forest area. The rate of carbon sequestration depends on species composition,the density of large trees in different girth classes, and anthropogenic disturbances in the present forest ecosystem.Further work is required to identify tree species having the highest potential to sequester CO2from the atmosphere,which could lead to recommendations for tree plantations in a degraded ecosystem.

Carbon budget·Carbon sequestration· Dipterocarpus·Biomass·Net production

Introduction

Tropical forests play an important role in reducing atmospheric carbon because they dominate the dynamics of the terrestrial carbon cycle.Tropical forests have the largest potential among the world’s forests to mitigate change through conservation of existing carbon pools,expansion of carbon sinks,and substitution of wood products for fossil fuels(Brown et al.1996,2000).Forests contain about 50%of the carbon stored in vegetation and about 50%of the carbon stored in the soil(TBFRA 2000). Biomass is the organic matter fixed by trees and is the source of all other productivity in the forest.Biomass can be used to:(a)determine energy fixation in forest(Brown and Lugo 1984;Brown 1997);(b)quantify increment in forest yield,growth,or productivity(Burkhart and Strud 1973;Thokchom and Yadava 2013;Debajit et al.2014), and(c)assess changes in forest structure(Brown 1997).

About1–2 Gtofcarbon are sequestered annually on land in temperate and boreal regions(Bousquet et al.2000). Tipper(1998)estimated thatdeforestation contributes about 1.8 Gt of carbon per year to the atmosphere.1.1–1.8 Gt C per year can be sequestered in 50 years in tropical forests (Makundi et al.1998).By estimating the role of forest vegetation in the storage and sequestration of carbon in the different forest ecosystem of the world,especially in the tropics,the data generated may be used to compute carbon cycling at the regional as well as the global level.

The forest under consideration is dominated by Dipterocarpus tuberculatus;other tree species are found but are not common,including Tectona grandis,Shorea robusta, and D.turbinatus etc.Limited information is available on the carbon budget and carbon sequestration of Dipterocarpus forests from India and,in particular Manipur, Northeast India(Supriya and Yadava 2006).The presentstudy was undertaken to evaluate carbon budgetand rate of sequestration of the Dipterocarpus forests of Manipur, North East India.We hypothesized that forests dominated by D.tuberculatus have higher biomass than the other codominant species due to the larger leaf area per tree basis. The species is fast growing and used as charcoal and timber;it also has high regeneration capacity through rootstock in spite of anthropogenic disturbance.

Materials and methods

The study site is located between 23°49′N and 24°28′N latitude and 93°45′E to 94°14′E longitude,at 300–360 m above the a.s.l.near Moreh town in the Chandel district, which is 108 km from Imphal,the capital of Manipur.The present forest is dominated by D.tuberculatus and occupies an area of 750 sq.km.It is located in Manipur,along the Indo-Myanmar border and extends up to South Asian countries of Myanmar,Thailand,Indonesia,Malaysia,and Philippines.

The climate of the area is dominated by monsoons,with warm moist summers and cool dry winters.The mean maximum temperature varies from 24.15°C(January)to 35.9°C(May)and the mean minimum temperature ranges from 4.5°C(December)to 21.1°C(August).The mean monthly rainfall ranges from 4.79 mm(January)to 195.88 mm(July).The mean annual rainfall is 1244.99 mm.The average relative humidity varies between 61.5%(February)to 82.8%(July).The length of dry period is 6 months.Soils are sandy in texture and acidic in nature.Soil moisture varies from 13.93±1.32 to 14.15±1.11%and soil organic carbon ranges from 3.44 to 4.41%.Total N and P ranges between 0.50–0.60 and 0.21–0.24%,respectively in the soils(Table 1).

Two forest stands of 0.1 ha each were chosen randomly for the presentstudy:Foreststand Iis on a flathilltop whilestand II is on a southern hill slope facing the Myanmar border.The forestis dominated by D.tuberculatus(locally known as Khangra)and represents young secondary forest, maintained by burning and sparse felling of trees by local inhabitants.In India,Dipterocarpus forests are recorded from the Western Ghats and north eastern states of India (Champion and Seth 1968).

Table 1 Physico-chemicalcharacteristics of soil in foreststand I and II(mean±SE)

To measure tree density,20 quadrats of 10 m×10 m were laid out randomly,based on line transects in each forest.The harvesting was done between October and November in both 2008 and 2009.Three individuals of each tree species were harvested from the quadrats for each girth class for all the species present in the forest stands. After harvesting,various parameters like diameter of the bole,at the base,the middle or center of the bole,total height of the tree,and total numbers of the leaves were recorded.The fresh weight of all boles,branches,leaves and fruits were determined at the site.

The sub-samples(three replicates)of different components were broughtto the laboratory in polythene bags.All the sub-samples were oven dried at 80°C to constant weight.Leaves of varying size(15 leaves)were also taken from each tree of different constituent tree species for determining leaf area.The biomass estimates for the standing crop of different tree species were computed using wood density values of different girth classes(Newbould 1967). The tree biomass was computed by multiplying tree density with biomass at each girth class of the species on hectare basis(Table 2).

The stand biomass was calculated by summing the biomass value across the girth class of all the species. Herbs and shrubs were harvested and weighed.Average biomass for herb and shrub species was multiplied by its respective density(individual ha-1)in the stand.Litter was collected from permanently laid quadrats of 1 m×1 m (10 each)randomly from both the stands and samples were oven dried at80°C to constant weight.Estimated biomass was used to estimate carbon stock(Brown 1997).

Aboveground net primary production was estimated by summing up the annual increment in the biomass and the corresponding litter fall deposited on the forest floor.Annual biomass increment was calculated by subtracting biomass in(year 1)from that of(year 2).The net productivity data is used to estimate the rate of sequestration by using a conversion factor of 50%.

Results

Tree layer biomass

Biomass increased consistently with the increase in the girth classes of all the three species.The biomass value ofD.tuberculatus in different girth classes ranged from 1233.05 to 3993.56 kg ha-1in stand I and 136.018–9581.085 kg ha-1in stand II.In Ardisia paniculata,it was 255.48–483.49 kg ha-1in stand I and 163.09–2388.51 kg ha-1in stand II in different girth classes.Wendlandia wallichii exhibited a biomass of 769.27 kg ha-1in the girth class of 10.1–20 cm.The total biomass for the tree species were recorded in the following order:bole＞branch＞leaf,except for D.tuberculatus (bole＞leaf＞branch).The total aboveground biomass of trees in site I was recorded to be 15.601 t ha-1and out of the total biomass,bole contributed 90.27%,branch 4.91%,and leaf 4.80%.In stand II,it was recorded to be 15.844 t ha-1,out of the total aboveground,bole contributed 60.68%,branch 13.25%,and leaf 26.50%.

Table 2 Total biomass of plant components in different diameter classes by tree species in forest site I(kg ha-1)(dry weight)

DBH/biomass allometric equation

In the two foreststands,the allometric relationship between increase in DBH and increase in biomass of different components was found to be highly significant.The value of r2was highly significant except in leaf of D.tuberculatus and A.paniculata and bole of W.wallichii in stand I. However,in stand II,only leaf of A.paniculata was found to be non significant.Thus it shows that with the increase in DBH,the biomass of the tree is also increased i.e.,DBH of the tree species and biomass of the tree components are positive correlation(Table 3).

Shrub and herb layer biomass

The shrub layer biomass in stand I was recorded to be of 6.35 t ha-1contributed by seven shrub species and in stand II,it was 1.432 t ha-1contributed by three shrub species (Table 4).Of these,Elaeocarpus chinensis and Actiphella exelsa exhibited the maximum biomass in stand Iand stand II,respectively.Albizia saman and Gynocardia odorata exhibited the minimum biomass in stand I and II,respectively.In herbaceous layer in stand I,nine herb species contributed a totalbiomass of 0.552 t ha-1,whereas a total biomass of 0.999 t ha-1was contributed in stand II. Among the herbs,Arundinella setosa and Kyllinga triceps contributed the maximum biomass in stand I and Imperata cylindrica in stand II.

Non-photosynthetic/photosynthetic ratio

The non-photosynthetic/photosynthetic ratio ranged from 2.098 to 7.852 for D.tuberculatus and 6.01 to 15.78 for A. peniculata for different girth classes;D.tuberculatus clearly exhibits the higher growth rate in comparison to other species.

Wet/dry ratio of biomass of different tree species in forest stand I and II

The wet/dry ratio of biomass of the tree species—D.tuberculatus,A.paniculata and W.wallichii—were recordedto be 2.35,2.42,and 2.40,respectively in foreststand Iand 2.17 for D.tuberculatus and 2.19 for A.paniculata in forest stand II(Table 5).

Table 3 Allometric relationship between DBH(X, cm)and biomass of tree components(Y,kg·tree-1)in foreststand I

Total forest aboveground biomass

In the forest stand I,out of the total aboveground biomass, trees contributed 68.51%,shrubs 28.96%,and herbs 2.5%.In the forest stand II,trees contributed 86.69%, shrubs contributed 7.83%,and herbs contributed 5.46% of the total biomass(Table 6).

Litter biomass

Annual litterfall varied from 5.33 to 6.20 t ha-1a-1in the two stands:D.tuberculatus shared 89.80%,A.paniculata 8.56%,and W.wallichii1.63%in stand I;D.tuberculatus contributed 96.74%and A.paniculata 3.25%in stand II (Table 7).Peak litter fall occurred in February coinciding with the cool and dry period of the year.

Net primary production

The total aboveground production was recorded to be 9282.73,848.80,and 294.44 kg ha-1year-1for D.tuberculatus,A.paniculata and W.wallichii respectively in stand I.The net primary production in different components of tree species and total aboveground net production of differentspecies in foreststands Iand IIhave been estimated and setin Table 5.In foreststand II,the net primary production in different components and total aboveground net production of D.tuberculatus and A. paniculata was recorded to be 5756.94 and 684.41 kg-1ha-1a-1respectively.Out of the total aboveground net primary production,the bole contributes 31.86%,branch 29.67%,and leaf 38.69%of the total net production in stand I.In stand II,the bole exhibited 32.64%,branch 31.72%,and leaf 35.63%outof the totalaboveground net production(Table 8).The distribution of total annual net primary productivity(TANPP)of different components is recorded in a sequence of leaf＞branch＞bole on both sites.

Carbon budget

The carbon content of the present study ranges from 0.127 to 3.500 t ha-1for stand I and 0.081 to 4.790 t ha-1for stand II,following the same proportional pattern as the total biomass of all the tree species on both the forest stands(Table 9).Like biomass,carbon density increases with increasing girth size for all of the tree species for both stands,except for D.tuberculatus in stand I,in which highest carbon content was recorded in the 30–40 cm girth class due to the presence of high density value.

Table 4 Density and biomass contributed by shrubs and herbs species in forest stand I and II

Table 5 Wet/dry ratio of biomass of different tree species in forest stand Iand II

Rate of sequestration

The rate of carbon sequestration varied from 147.22 to 4641.36 kg ha-1year-1in forest stand I,whereas in forest stand II,it varied from 677.18 to 3753.34 kg ha-1year-1(Table 9).The maximum rate of sequestration was recorded in D.tuberculatus,followed by A.paniculata,W. wallichii in forest stands I and II.

Table 6 Biomass contribution by trees,shrubs and herbs in forest site I and II

Discussion

The density of herbs and shrubs was less in forest stand II as compared to stand I;the reason may be that a higher density of tree species was recorded in forest stand II.The number of saplings are higher than the number of big trees in foreststand I because itis situated ata plain topography,people used to cut the bigger trees for charcoal,fuel wood, and timber.The higher biomass contribution by D.tuberculatus in both forest stands may be due to the availability of higher girth classes and higher density in comparison to the other two species,A.paniculata and W.wallichii.In forest stand II,W.wallichii was present only on seedling stage.The present forest is very young,that is,secondary forestand biomass of differentplantcomponents as wellas total biomass increased with the increase in girth class.

Dipterocarpus tuberculatus contributed a higher percentage of total biomass in different girth classes in both foreststands,this may be due to the large leaf area per tree basis,high regeneration capacity from rootstock,and fastgrowing species.D.tuberculatus is a broad-leaf tree species exhibiting maximum leaf area and biomass even though it has fewer leaves in comparison to A.paniculata and W.wallichii.Though the higher value of tree biomass was recorded in forest stand II,the total biomass (tree+shrub+herb)was higher in stand I,which may be due to the presence of higher contribution from shrubs species in stand I than that of stand II.

The standing crop biomass of the present forest stands was lower than the value for dry deciduous forest and salforest reported by Singh et al.(1992),Singh and Yadava 1994 for mixed oak forest in Manipur,India,Kawahara et al.(1981)for lowland Dipterocarp forest,in the Philippines.However the value is higher than the value reported by Lim and Md.Basri(1985)for the secondary forest in Sibu,which was dominated by macaranga,mallotus,ficus, and vitex.The forest is at early stage of succession.The presentvalue in kg tree-1for both forestsites lie within the value reported by Misra et al.(1967).The value reported for aboveground biomass of several other species ranged 34.2–599.6 kg tree-1for sub-tropical broad leaf trees at Yona,Japan(Kawavabe 1977).

Table 7 Annuallitterfall and%contribution in forest stand Iand II

The values of total annual litter biomass in the present forest lies well within the value reported by Golley et al. (1962)for tropical forests and dry deciduous forests reported by Singh et al.(1992).The present value of net primary productivity lies near the value reported by Singh et al.(1992)for dry deciduous and sal forests in India and lower than the value reported for mixed oak forest(Manipur,India)by Singh and Yadava(1994)and Whittaker and Wood(1969).Artand Marks(1971)reported 8.59 and 7.12 t ha-1a-1in two differenttemperate deciduous forest stand of Brookhaven in New York.The low value of net primary production in the present study site may be due to young forest trees and the fact that the forest is at successional stage owing to biotic disturbance.

The carbon stock in the present dipterocarp forest is lower than the value of dipterocarp forest of Philippines (Lasco and Pulhin 2003;Lasco etal.2006),the dipterocarp forest of Mindanao(Kawahara et al.1981),Seima protection forest,Cambodia(Khun et al.2012)and for Indian forest i.e.,Dipterocarpus forest,S.robusta and Boswellia serrata(Manhas et al.2006),and the secondary tropicalforest of Singapore(Ngo et al.2013).The value of the present study is lower because the forest is a secondary forestand though dominated by fast-growing species of D. tuberculatus,it is subject to logging and shifting cultivation.However,the present value lies near the value reported by Racelis(2000),for the Dipterocarp forest of Makiling,Philippines.

Table 8 Net production in tree species and net production in different plant components of tree layer on forest stand I and II(percentage contribution of different species kg ha-1a-1)

The rate of carbon sequestration is highly variable and depends on the species composition,age of the forest tree and climatic factors.Data are still limited on carbon sequestration compared to carbon stocks.The rate of sequestration in the present forest is higher than the value reported by Lasco and Pulhin(2003)for natural forests in the Philippines and Racelis(2000)for the Dipterocarp forest of Makiling,Philippines.However,it is lower than the data reported by Lasco and Pulhin(2003)for fastgrowing tree plantations in the Philippines and by Miah et al.(2011)for forests in Bangladesh.

The current study shows that Dipterocarpus forests have considerable potential to store carbon,due to the relatively young age of the forests and high rate of productivity.Reforestation will be required to sequester more carbon.Ongoing anthropogenic activities—such as shifting cultivation,extraction of fuel wood,and charcoal production—that lead to increases in CO2in the atmosphere can also be sequestered by increasing the rate of reforestation.

AcknowledgmentsThe first author was grateful to Department of Science and Technology,Government of India,New Delhi for providing me financial assistance as Woman Scientist.

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20 August 2013/Accepted:16 February 2014/Published online:30 April 2015

?Northeast Forestry University and Springer-Verlag Berlin Heidelberg 2015

The online version is available at http://www.springerlink.com.

Corresponding editor:Hu Yanbo.

?L.Supriya Devi supriya_lus@yahoo.com

1Department of Life Sciences,Manipur University, Imphal 795003,India