Carbon footprint of thermal energy production from poplar short-rotation coppice plantations

The use of agroforestry biomass represents a relevant aspect in the world debate on the issue of reducing the climate-altering gases into the atmosphere. in fact, as a renewable energy source, woody biomass can play an important role in replacing fossil fuel in the production of thermal and electrical energies. One of the possible sources of wood biomass production is represented by poplar SRC plantations. In the present work the Global Worming Potential (GWP) of the entire supply chain of four different cutting shifts (2, 3, 4, and 5-years) have been evaluated according to the IPCC method. The productive cycle of the plantation was 16 years (2- and 4-years shifts), and 15 years (3- and 5-years shifts). For production cycles of 2- and 3-years, two biomass harvesting systems were considered: the first one by carrying out a single step with a dedicated machine (forage harvester); the second one using different machines to perform first the felling, then the logging of whole trees and subsequently, the chipping of staked trees. Two options were considered also for 4- and 5-years shifts: the first one involves manual felling with a chainsaw, logging of whole trees with winch and subsequent chipping of them; the second one considers the use of a feller-buncher for felling, a skidder for logging and a chipper before using the woodchips in the boiler. It was considered that the biomass produced was used in a biomass plant for heating a public building. The environmental impact of 1 GJ of heat energy produced by the various forest rotation plants were assessed considering the entire life cycle, from the field stage to the thermal energy production. The results were compared with the production of the same thermal energy using a diesel boiler. The field stage has contributed to greater environmental impact due above all to fertilization and fuel consumption for the execution of mechanical processing, the collection and chipping of the biomass produced. The comparison between the two systems has shown that the production and use of biomass to generate thermal energy can reduce the Global Worming Potential by more than 50% compared to the use of fossil fuels.