Landscape can play a role in the moisture content of temperate fuels

Abstract Background Fuel moisture content (FMC) is a critical component of wildfire risk. The spatiotemporal patterns of FMC of many key live, dead and surface-level temperate fuels (e.g. heather ( Calluna vulgaris ), gorse ( Ulex europaeus ), bracken ( Pteridium aquilinum ), moor grass ( Molinia caerulea ), litter, organic soil layers) are largely unknown and unravelling the drivers of FMC is challenging. Current models designed to predict FMC, principally of dead fuels, generally consider only weather variables. However, landscape variables (such as elevation, slope, aspect, soil type) affect water retention and availability of moisture within soils, and are therefore likely to influence FMC of live and organic ground fuels. We carried out a large-scale fuel sampling campaign from 2021–2023 of eighteen different fuel types across 43 sites through six different climate regions of the UK. We implemented a two-stage modelling approach to determine the influence of weather, phenological, and landscape variables on FMC. Results We found that landscape influences the FMC of eleven fuel types, particularly for the organic soil layer, followed by live gorse stem and live bracken leaves. The FMC of all surface fuel types (moss, litter, organic layer and twigs) and six of the seven live fuels were influenced by landscape. Only one dead fuel type was influenced by landscape variables. Of the landscape variables, soil type, land cover and elevation significantly influenced fuel FMC. Slope and aspect did not influence the FMC of any fuel types. Weather influences the FMC of most fuel types, and phenology largely only influences the FMC of live and surface fuels. Conclusions We have shown that landscape variables are important to consider when developing fuel moisture models, but that this is mainly important for live fuels and organic ground fuels. We therefore recommend tailoring models to each fuel type to yield the best performance.