Environmental filtering along resource gradients is a central mechanism shaping local species assemblages, yet how soil and litter chemistry mediates this process for epigeic arthropod communities remains incompletely understood. We investigated how variation in soil and leaf litter chemistry structures carabid assemblages in a temperate arboretum comprising nine monoculture stands. Ground beetles were sampled using pitfall traps across six sampling periods over three years, and assemblage composition was related to environmental variables using redundancy analysis. Carabid assemblages were significantly structured by soil and litter chemistry (RDA, p = 0.005), with pH and phosphorus content emerging as the main gradients, explaining 26.1% and 13.5% of the variation in species composition, respectively. These gradients were consistent with patterns identified by principal component analysis, which indicated that litter chemistry—particularly pH and nutrient-related variables—was the primary source of environmental differentiation among stands. In contrast, univariate models showed limited responses of community-level diversity metrics to these gradients: neither species richness nor Shannon diversity varied significantly with pH or phosphorus, whereas epigeic activity declined along the phosphorus gradient. These results indicate that soil and litter chemistry structures species composition through environmental filtering, but its influence on aggregate community metrics is weaker and primarily expressed through changes in activity rather than diversity. Overall, our findings highlight the importance of belowground chemical gradients, which co-vary with overstory composition, as filters shaping carabid assemblage composition and activity.