There hasbeen considerable and growing interest in forest carbon and its role ininternational climate change policy. This interest stems from the substantialgreenhouse gas (GHG) emissions that arise from the forestry sector and thepotential for forests to deliver cheap-and-deep emission reductions (Watson, 2009). Forest ecosystem plays very important role in the global carbon cycle asit stores about 80% of all above-ground and 40% of all below-ground terrestrialorganic carbon (Change, 2001) .
The roles and impacts of biomass on carbon cycles, soil nutrientallocations, fuel accumulation, and habitat environments in terrestrialecosystems have long been recognized (Luet al. 2016). Biomass governs the potential carbonemission that could be released to the atmosphere due to deforestation.Understanding the potential of forest ecosystems as global carbon sinksrequires a thorough knowledge of forest carbon dynamics, including bothsequestration and fluxes among multiple pools. Forest or vegetation carbon essentiallyconsists of the biomasswhich is defined as mass of live or dead organic matter.
Vegetation carbonexerts a tremendous influence of global climate. The fact that the mountainforests are such a huge reservoir of carbon, the size of the carbon poolcontained therein and the associated changes hold high relevance for climatechange policies (Price, Gratzer, AlemayehuDuguma, Kohler, & Maselli, 2011). As the changes in biomassdensity (i.e. vegetationbiomass per unit area) can act as a proxy to sequestration or release of carbonfrom atmosphere, the biomass density can also be used as an essential climatevariable (FAO2009).
The accurate quantification of biomassis important to better understand forest productivity and carbon cyclingdynamics. Accurate delineation of biomass distribution at scalesfrom local and regional to global becomes significant in reducing theuncertainty of carbon emission and sequestration, understanding their roles ininfluencing soil fertility and land degradation or restoration, andunderstanding the roles in environmental processes and sustainability (Foody, 2003) . Stand-basedinventories (SBIs) are widely used for quantifying forest characteristics andfor estimating biomass, but information may quickly become out dated in dynamicforest environments.
Though satellite remote sensing may not be completesubstitution but it can be an important supplement. In recent years remotesensing techniques have become prevalent in estimating AGB (Lu2006). Spectral signatures or vegetationindices are often used for AGB estimation. Many vegetation indices have beendeveloped and applied to biophysical parameter studies (Anderson, Hanson, & Haas,1993; Mutanga & Skidmore, 2004). Vegetation indices have beenrecommended to remove variability caused by canopy geometry, soil background,sun view angles, and atmospheric conditions when measuring biophysicalproperties (Elvidge & Chen, 1995). However, not all vegetation indicesare significantly correlated with AGB. In general, vegetation indices canpartially reduce the impacts on reflectance caused by environmental conditionsand shadows, thus improve correlation between AGB and vegetation indices,especially in those sites with complex vegetation stand structures (Luet al. 2004).
A combination of spectral andspatial information extraction techniques shows promise for improvingestimation performance of forest stand parameters (M. Wulder, 1998). 1.1 Forestcarbon and its measurement:Duringproductive season, CO2 from the atmosphere is taken up by vegetationand stored as plant biomass. In the presence of chlorophyll, the CO2from the atmosphere and water get converted to sugars by taking the energy fromthe sunlight in the process called photosynthesis. The internal metabolism ofthe tree consumes about half the sugars and the remaining half is used forbuilding of wood, roots and leaves. This constitutes the biomass of the tree.
About half of this biomass is carbon content of the tree (McKinley et al., 2011). The consequent changes in vegetationcarbon pools are in certain ratio of this biomass. Biomass, in general,includes the above-ground and below-ground living mass, such as trees, shrubs,vines, roots, and the dead mass of fine and coarse litter associated with thesoil.
This natural mechanism of carbon sink in trees is a dynamic phenomenon.The percentage of carbon in live and dead trees is to the tune of 60% in amature forest while soil and forest litter store about 40%. The ration of carbon in live and dead trees depends on theforest age (Ryan, Harmon, Birdsey, & Giardina, 2010).Among all theterrestrial ecosystems the highest carbon density is found in forests andtherefore forests act as a natural brake on climate change (Gibbs, Brown, Niles, & Foley, 2007).
The carbon pools ofterrestrial ecosystems can be divided into two groups namely above-groundbiomass and the below-ground biomass (FAO, 2009). Among thesedifferent pools of vegetation carbon the most critical one is the abovegroundliving biomass of trees as this is typically the largest contributor and themost directly impacted by anthropogenic activities and by deforestation anddegradation. Thus, in the quantification of carbon stocks and fluxes fromforests, the assessment of aboveground forest biomass carbon becomes the mostcritical step (Gibbs, Brown, Niles, & Foley, 2007). Particularly for the forest ecosystems, themeasurements of belowground biomass are laden with poor accuracy; they are timeconsuming and labour intensive and mostly derived from the above groundbiomass.
Keeping in view these facts,this study has dealt only with the above ground forest biomass. Biomasscan be measured in a number of ways. Each method has its scope of applicabilityin space and time. In situ samplingmethods include destructive and non-destructive methods. Actual physicalmeasurements of attributes like forest inventories, and productivity can bedone either at some sample plots or across a network of plots but it isdifficult to scale them up for a larger landscape (Prentice & Bondeau, 2007).
Harvesting alltrees in a known area would be the most accurate method for forest carbonestimation for a particular location but it would be prohibitivelytime-consuming, expensive, destructive and impractical for country-