Public Land Use Effects on Soil Carbon in Tamarix arceuthoides Dominated Dryland Forests

Abstract In arid and semi-arid ecosystems, soil organic carbon (SOC) is generally low and highly vulnerable to anthropogenic disturbances. Tamarix species, common in arid floodplains, can enhance soil structure, trap fine sediments, and increase carbon stocks, yet their resilience to human trampling remains poorly understood. This study assessed the effects of recreational trampling on soil carbon dynamics in Tamarix arceuthoides stands in southwestern Iran. We compared undisturbed and disturbed stands across two sites, measuring tree characteristics, aboveground biomass, soil physicochemical properties, and carbon fractions (labile, recalcitrant, and total SOC) in 10 × 10 m quadrat alongside transects with 150 m interval between plots. Results showed that disturbances reduced SOC by 483%, labile carbon by 328%, recalcitrant carbon by 236%, and total soil carbon stock by 443% relative to undisturbed stands. Tree biomass and density declined significantly, while crown diameter and height remained unchanged. Disturbed sites exhibited significant lower soil nitrogen, phosphorus, potassium, moisture, and silt, but higher sand content. Outdoor camping and driving vehicles through the woodlands caused soil organic matter and vegetation cover removal and make it susceptible for soil erosion and physical changes (silt and sand). Principal Component Analysis clearly separated disturbed from undisturbed stands, with soil texture, nitrogen, and organic carbon as key drivers of variation. Carbon fractions were strongly positively correlated with nitrogen, silt content, and tree biomass. These findings demonstrate that human trampling substantially diminishes carbon pools in Tamarix stands by degrading vegetation and soil structure, highlighting the need for management strategies to protect soil carbon sequestration.