I have not used it myself, but Heureka is used by several researchers at my university. It has been developed for Swedish forests, but I believe it is worth looking into. It might be possible to adopt it to Himalayan conditions if you have the necessary data.

http://heurekaslu.org/wiki/About_Heureka

I have never used an ecological software for modeling carbon status of forest. We are still looking for establish an ecological modeling software for carbon status of african forest. I don't think the common software (Heureka) usually used could work with any geographical forest 

For some ideas, please see attached.

Article Carbon Stock of European Beech Forest; A Case at M. Pizzalto, Italy

I think your question needs to be more clearly posed.

What input variables will be measured?  What precisely do you want predict, and over what time scale?  It's not really clear that you need a "model" (of, say, stand dynamics or ecosystem processes) unless you plan to project future carbon balance of stands.

If you have "timber cruise" or similar data available, you can obtain estimates of aboveground or total forest carbon stocks using allometric models and conversion factors from biomass to carbon.  If you have only remote sensing data available, then other methods will be necessary, but this depends critically on the data inputs.

In all cases you will need to convert from estimated biomass to carbon of the stands.  The attached publications synthesizes the global data available for this part of the problem.

Data Carbon Content of Tree Tissues: A Synthesis

I propose Carbon Budget Model:it is used in Canadian Forest Sector.It has strong components of ecological process modelling even though its works best in managed forests .i.e plantation forests

There is no model better than others. Which model to use depends on the spatial and temporal scales in which you are interested, in the type of ecosystem, the information that you have available and your specific question. If you don´t know these before starting your work, you may end up using models that are not adequeate to your needs. I suggest starting by reading the different reviws on forest models that have been published in the last years, where comparisons and descriptions of diferent models are provided.

Article Geospatial analysis of forest fragmentation in Uttara Kannad...