WHS projects can be classified based on the source of woody material.

In the first type (TYPE A), woody biomass residuals are collected, often with environmental co-benefits such as fire risk reduction and waste utilization. They are ‘low-hanging fruits’, limited by the availability of wood residuals that would be otherwise mulched, burned, or left to rot. This method may have a potential of up to 2 GtCO2 per year globally.

In the second type (Type B), wood is harvested or collected from a sustainably managed forest, such as timberland and secondary-growth forest. The operation can be repeated every few years or decades and the carbon sequestered accumulates over time. Type B has large potential, up to 10 GtCO2 per year globally (about one third of global fossil fuel emissions).