Gradients of geochemical change in relic charcoal hearth soils, Northwestern Connecticut, USA

•Soils from 18th–20th century charcoal hearths were analyzed across Connecticut, USA.•Available phosphorus is more than 200% lower in hearths soils than adjacent soils.•Hearth soils are enriched in organic carbon and extractable cations Ca2+, Mg2+, Na+.•Hearths with two charcoal layers indicate multiple episodes of charcoal production.•Charcoal dispersal increases the area of impact for individual hearths by 30×. Relic charcoal hearths (RCHs) have produced distinct legacy effects in forest soils around the world. Recently, LiDAR imagery has revealed thousands of 18th–early 20th century RCHs in Litchfield County, Connecticut, USA; however, the effects of RCHs on a landscape-scale are not well-documented, particularly fine-scale heterogeneity within RCHs and surrounding soils. This study examines the long-term impacts of charcoal production by measuring RCH soil chemical and physical properties from three perspectives: (1) compared to adjacent reference sites (RSadj), (2) laterally at systematic distances away from the RCH center, and (3) vertically within the RCH soil profile. Mean charcoal abundance was greater in RCH sites than RSadj (p