Drought risk to timber production – A risk versus return comparison of commercial conifer species in Scotland

Climate change will alter precipitation patterns across the world increasing drought risk to forests in some areas, especially where summer precipitation is reduced. Effective management of this risk requires quantified information on the probabilities and consequences of drought to support policy and strategic decisions on the choice of tree species that will provide drought resilience and ensure continued timber supply. Here we define a new approach to delivering this information to underpin management decisions on species choice for restocking. We derive location-specific risk versus return analyses, for twenty commercial timber species in Scotland, by quantifying the impact of drought risk under a high emission scenario on potential return, modelled as change in baseline volume of timber production (yield in m³ ha⁻¹). We find that the current potential yield of Sitka spruce is likely to be sufficiently high to compensate for its relatively high drought susceptibility compared to alternative species, modelled over a new 50-year rotation. In regions projected to experience increased drought risk - particularly central and eastern areas of Scotland - the higher drought tolerance of some species means that they are likely to be viable alternatives to Sitka spruce, based on a threshold productivity which we set for the purposes of this analysis as ≥90% of predicted Sitka spruce yield. Since species diversification is a potential strategy to increase forest resilience against other risks, such as those from pest and diseases, our analysis provides a framework within which these regional decisions can be made. Risk management strategies should be introduced which include the risk from drought to commercial softwood plantations and thereby help protect timber volume production. The modelling approach outlined could be adapted to compare timber species in other regions where comparable data are available.