Also, calculating carbon can be tricky. The roots of the tree, leaves that are falling down etc all have carbon. Getting a correct estimate of the carbon fixed in roots or the leaves involves good estimation of the tree mass, green mass, carbon mass. These change as per the tree / shrub / grass etc. But all in all, the calculation is challenging.
Accurate assessment of the carbon fixed helps in any country or community to see what has been done and what more needs to be done. Ex from traditional estimates, one might see the carbon fixed as 1000 MT. But with accuracy and calculating the mass of tree, green mass and carbon mass of a tree, one can understand that it’s perhaps only 400 MT. Which means that there is much more to do in terms of actual carbon fixing. More trees need to be planted, taken care of and then the carbon fixing keeps on increasing at a rate which is needed.