I agree with the above answers, at the same time forest soils are called as Virgin Soil, having higher Carbon in the soil. If we harvest the vegetation from this virgin soils for any purpose leads to carbon debt because of negative sequestration rate. 

We reviewed some of the relevant literature on biofuels and carbon debt in this paper from 2015: 

Article A polymorphic approach to policy analysis: A case study of o...

Clearing natural forests to biomass agriculture most likely to cause carbon debt, at least for several decades, if not for centuries.

Whether biomass agriculture will lead to carbon debt or carbon credit could depend on several factors such as: biomass crop type, input required for biomass crop production, the difference in carbon stocks between the biomass crop and the pre-existing vegetation and the technology use in the conversion of biomass to usable energy (Field et al. 2008, pl. see the link).

http://www.cell.com/trends/ecology-evolution/abstract/S0169-5347(08)00009-8?_returnURL=http%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0169534708000098%3Fshowall%3Dtrue

Thank you both for sharing your views. This is particularly important as the fear of carbon debt or indirect land use change impact of bioenergy hampering the progress of bioenergy. I am not precisely sure what quantum of positive carbon will be added to the atmosphere by replacing forest with biofuel but certainly biofuel cultivation in forest lands will result in permanent biodiversity loss. 

I agree with the above answers, at the same time forest soils are called as Virgin Soil, having higher Carbon in the soil. If we harvest the vegetation from this virgin soils for any purpose leads to carbon debt because of negative sequestration rate. 

... In the balance, and amongst other reasons, any replacement of any amount of biomass with a smaller stock of biomass will cause a carbon debt. It does not matter if you have a faster turnover in the rotation of biofuel crops with respect to the previous forest biomass; as a high portion of the biofuel mass will produce CO2 whilst the forest would store it. Perhaps the only advantage we can get from biofuels is that, tendentially the combustion is cleaner than combustion of hydrocarbons.

Thanks for every one react with this important  idea, but nowadays the bio-fuel crops has not commercially benefits as the lowest of oil price. 

Thanks everyone for bringing new knowledge via this discussion. We will surely find alternatives to fossil fuels ( e.g., energy from water, sun) but clearing forest for planting renewable fuel is fundamentally wrong. Forest is not just a carbon stock, it's habitat of billions of animals.

I agree with previous answers, but would just like to bring to the attention here that there is an important aspect related to time in the carbon debt question which is not directly reflected in the type of metrics normally used to assess bioenergy and biofuels with LCA and related methodologies.

The C debt does indeed occur when you initially change land use and decrease the C stocks in living biomass and soils due to the production of dedicated bioenergy/biofuel crops. The time it takes to compensate this initial additional C emission to the atmosphere through the effect of replacing fossil emissions with the biofuel is the C payback time. After this the biofuels actually will be beneficial from a climate change mitigation perspective. So, there is an aspect in this related to long term versus short term impact trade-offs which might be relevant from a policy perspective.

I think it is easier to understand the dynamics when using time-dependent, absolute and instantaneous indicators in the assessment of climate impacts. Here are two papers with examples of how land use change leads to C stock changes and time-variable climate impacts. The first one shows how the C debt created by extracting logging residues previously left in the forest affects the climate over time. The second is my thesis that shows how the establishment of a willow plantation on previously C depleted soils can actually increase C in the system (the opposite of a C debt) and how this can help mitigate climate change (as long as the change is global warming).

I think you will find the article of Canadell et al. (2014) on biospheric carbon management interesting and relevant as well.

http://dx.doi.org/10.1007/s12155-015-9649-3

http://dx.doi.org/10.13140/RG.2.1.3508.0164

http://dx.doi.org/10.1038/ncomms6282

Thank you Dr. Ericsson for the interesting note on carbon payback time and time-dependent carbon debt.

I also feel it is important to carefully consider the whole carbon cycle, i.e. flux of carbon among its reservoirs. Rocks and oceans are the greatest carbon banks followed by atmosphere and soil-plant biomass. I don't know if we can manipulate the carbon flux between atmosphere and ocean and make ocean as carbon bank for additional carbon emitted from fossil fuel burning.

I hope I am not misinterpreting you Dr Hiloidhari. Are you asking if it is possible to manipulate the oceans to increase its function as a C sink? There has certainly been suggestions such as priming the biological pump (increasing the transport of dead biomass downwards) and CCS solutions. The trick is that it has to reach the deep ocean, and that is not a small trick.

There is however a problem involved with using the ocean as a C sink to counteract fossil fuel CO2 emissions. That is that continous emissions from fossil fuels increases the CO2 level both in the atmosphere and the surface layers of the ocean before it eventually reaches the deep ocean through natural mechanisms. Increased CO2 in the surface layer is harmful to many marine organisms. The most well known victims are the coral reefs. To avoid this more CO2 would have to be captured using CCS than what is emitted from fossil fuels. That would solve things for sure, but who is willing to pay for it?

Thanks Dr. Ericsson for answering my query. I recently read an article reporting the declining carbon accumulation capacity of amazon forest. This is really an alarming issue.

Where is a solution to this 'energy-emission-environment' debate?

http://www.nature.com/nature/journal/v519/n7543/full/nature14283.html

Thanks for bringing this up!  This situation of having forest lands being cleared for biofuel cultivation shouldn't ever happen but unfortunately it does. Per your question growing biofuels on forest land certainly affects the carbon balance and indeed does contradict any intended climate change benefits.  On the possible way forward, countries should as a first step undertake an agro-ecological zoning (AEZ) which clearly demarcate areas to grow biofuels (or not). The AEZ should also take into consideration other key sustainability aspects (indicated in our publications below).  We have undertaken a number of studies that throws light on aspects of this particular issue where we provide informed analysis on the possible way forward including:

Dr. Emmanuel Ackom,

UNEP DTU Partnership

Denmark

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