Fourfold increase in fragmentation from road expansion in Siberian intact forests since 2000.

Road development is a major driver of forest degradation worldwide, accelerating habitat fragmentation, biodiversity loss and carbon emissions. Although these consequences have been documented in tropical forests, the spatiotemporal dynamics and ecological impacts of road expansion in boreal intact forest landscapes (IFLs) remain poorly understood, particularly for the central-eastern Siberian IFLs, an ~1.71 million km2 wilderness and carbon sink. To address this gap, we analysed 20,480 Landsat satellite images from 2000 to 2023, and found a 1.6-fold increase in road area and length across this region. Road expansion, spatially linked to logging and mining activities, occupied ~1,046 km2 of IFLs, intensified forest fragmentation 4.3-fold and increased IFL edges within 30 m of roads 1.2-fold. Between 2010 and 2023 alone, road expansion directly contributed to 39.1 megatonnes of aboveground biomass loss. These findings highlight the urgent need for improved road planning and policies that balance economic development with boreal forest conservation.