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Abstract

Podzolic soils, typically dismissed as 'unfarmable,' were transformed by Sts'ailes peoples into nutrient-dense substrates capable of producing forest foods from native species (Armstrong et al., 2023; Oberndorfer et al., 2020). This transformation was achieved through diverse ancestral land management (ALM) techniques practiced for thousands of years, creating food-producing landscapes that sustained local populations (Ritchie et al., 2025; Vanier et al., 2024). Utilizing mass spectroscopy instruments at PCIGR and UBC's SoilRes3 lab, this research investigates the geochemical signatures of ALM practices by the Sts'ailes First Nation in the Harrison River watershed, British Columbia. Indigenous forest gardens—cultivated through cultural burning, organic amendments, and selective species management—are compared to adjacent periphery forests to understand how millennia of land stewardship shaped soil properties. Soil samples from forest garden and periphery forest sites at two slough systems (Ed Leon and Phillips) were analyzed for physicochemical properties, exchangeable and bioavailable nutrients, total and trace element concentrations, including rare earth elements (REEs) and lead isotope ratios. Despite locally comparable baseline geochemical environments, Phillips forest gardens showed statistically significant enrichments in exchangeable cations (Al, Ca, K, Mg, Na) and bioavailable nutrients (B, Ca, Mg, Mn, Na, P, Zn), alongside lower C:N ratios indicating enhanced microbial activity and nutrient cycling. Crab apple leaf analyses revealed lower heavy metal uptake in forest gardens, suggesting effective trace element immobilization through organomineral complexation. The Ed Leon slough exhibited fewer distinctions between forest gardens and periphery forests, attributed to coniferous forest encroachment following colonial displacement and cessation of active management. REE fractionation patterns, particularly La/Lu ratios normalized to parent material, revealed differential weathering regimes: forest garden soils demonstrated relative HREE depletion in B horizons compared to C horizons, contrasting with periphery forest enrichment patterns, suggesting enhanced mineral protection through organic matter complexation in managed soils. This community-centred research demonstrates that ALM created geochemically distinct, nutrient-rich soil systems with persistent legacy effects centuries after management ceased. The findings challenge colonial soil classification frameworks, demonstrate the ecological benefits of Indigenous land stewardship, and provide a geochemical foundation for contemporary forest garden revitalization efforts.