Informing afforestation decisions with expert knowledge on forest biodiversity

Abstract

Biodiversity underpins the ecosystem services provided by forests, yet for several planting scenarios expected to play an increasing role in future afforestation, the absence of comparable biodiversity data constrains ecosystem service modelling, natural capital accounting and associated economic valuation, thereby limiting evidence-based decision-making. To address this gap, we used expert elicitation through a Delphi survey to generate numeric biodiversity scores for three managed monoculture plantation forests representing a fast-growing conifer, a fast-growing broadleaf, and a slow-growing broadleaf taxon. Experts evaluated sixteen afforestation scenarios differing in tree species, forest development stage, soil type, and management context, across three broad biodiversity indicators. This approach provides a practical method for generating comparable biodiversity indicators across afforestation scenarios when empirical data are incomplete. The resulting scores reproduced well-established ecological patterns reported in the literature, including higher biodiversity in broadleaf plantations relative to fast-growing conifers and increasing biodiversity with forest structural development. Patterns were broadly consistent across expert groups and aligned with available National Forest Inventory data for Sitka spruce. These findings suggest that structured expert elicitation can generate ecologically meaningful biodiversity indicators where empirical data are limited. As afforestation policies increasingly promote diverse planting scenarios under changing climatic and ecological conditions, decisions will often need to be made before comprehensive field data become available. By synthesising expert knowledge, this approach generates biodiversity indicators that can be incorporated into economic and environmental modelling frameworks used to inform land-use planning and afforestation policy. In contexts where empirical data are limited, expert elicitation can therefore help decision-makers evaluate the potential biodiversity implications of alternative afforestation strategies.