Dear Binay Sa 

In allometric equations you don't need density (including wood density and bark density) to estimate biomass. but in volumetric equations you have to know the value of wood and bark density to estimate the amount of biomass.

This is the main difference.

Dear Ardalan Daryei,

Your answer is interesting. Could you tell me which equations will be better to use .. allometric or volumetric ??

Allometry is the most common and reliable method for biomass estimation.

Basically both of them are the same.

If you cant develop allometric equations by harvesting method (cutting trees) then you can use volumetric equations and wood density to develop allometric equation.

Both are the same.  Volumetric method is one of many allometric approaches for tree biomass or volume...