Identifying non-agricultural marginal lands as a route to sustainable bioenergy provision - a review and holistic definition

Concerns regarding global food security, direct or indirect land use change from bioenergy production require a better understanding of the alternative landbanks that may exist. The potential of 'marginal' land, whether for food or fuel production, has been the subject of much previous research but is currently compromised by the lack of a clear, globally accepted definition. A critical omission in the plethora of existing explicit or implicit definitions in use is the lack of comprehensive or consistent inclusion of non-agricultural land types, here re-defined as those now rendered unsuitable, unacceptable or permanently unavailable for food purposes. The result is variable inclusion of such land types in different areal studies, uncertainty regarding the nature of any land identified as 'marginal', in turn leading to inconsistent estimates of the role they could play in the provision of sustainable bioenergy. The purpose of this research is to review the full range of possible 'marginal' land resources, especially those which are non-agricultural so avoid food competition, from previously-developed brownfield land, to former landfills or old mineral workings. Literature examples are compared to determine which land types have actually been included and quantified. In these case studies, non-agricultural types may equal other marginal lands at country or provincial scale, becoming dominant in urban regions. An inclusive definition is proposed, together with a graphic classification scheme, to guide future studies and enable quantification of truly non-agricultural marginal land as a potential contribution to sustainable bioenergy provision as part of the net zero, circular economy.