Pyrolysis of invasive woody vegetation for energy and biochar has climate change mitigation potential

Abstract

<p>Woody plant encroachment in agricultural areas reduces agricultural production and is a recognised land degradation problem of global significance. Invasive native scrub (INS) is woody vegetation that invades southern Australian rangelands and is commonly cleared to return land to agricultural production. Clearing of INS emits carbon to the atmosphere, and the retention of INS by landholders for the purpose of avoiding carbon emissions has been incentivized in Australia as an emission reduction strategy. Retaining INS, however, means land remains relatively unproductive because INS negatively impacts livestock production. This desktop study examined whether clearing INS to return an area to production, and pyrolysing residues to produce biochar, has the potential to provide climate change mitigation (the "pyrolysis scenario"). The syngas produced via pyrolysis was assumed to be used to generate electricity that was fed into the electricity grid and avoided the production of electricity from existing sources. In addition, the biochar was assumed to be applied to soils used for wheat production, giving mitigation benefits from reduced N2O emissions from fertiliser use and reduction in the use of lime to ameliorate soil acidity. Relative to clearing INS and burning residues in-situ, the pyrolysis scenario resulted in a reduction in radiative forcing of 1.28 × 10⁻⁴ W m² ha⁻¹ of INS managed, 25 years after clearing, and was greater than the reduction of 1.06 × 10⁻⁴ W m² ha⁻¹ that occurred when INS was retained. The greatest contribution to the climate change mitigation provided by the pyrolysis scenario came from avoided emissions from grid electricity production, while avoided N2O and lime emissions made a relatively minor contribution towards mitigation.</p>