More Than Two Decades of Ungulate Exclusion Did Not Alter Soil Organic Carbon Stocks in a Temperate Primeval Forest

ABSTRACT The effects of long‐term wild ungulate exclusion on soil organic carbon (SOC) storage and soil organic matter (SOM) properties in forest ecosystems remain uncertain. Past research has been limited by short exclosure duration, shallow sampling depth, and confounding factors. We addressed these shortcomings by studying 23‐year‐old ungulate exclosures in the strict reserve of the Białowieża National Forest (eastern Poland) that has been protected from major human disturbances for centuries. The study also evaluated the effects of tree species composition, tree species diversity, and soil texture. Large ungulate exclusion decreased bulk density in the mineral soil, increased the C:N ratio in 5–10 cm and 10–25 cm soil layers but did not affect SOC stocks in the forest floor (FF) or mineral soil. Additionally, exclusion did not affect the partitioning of carbon between mineral‐associated organic matter (MAOM) and particulate organic matter (POM) fractions in the uppermost soil layer (0–5 cm). Higher tree species diversity was associated with lower soil C:N ratios, whereas a greater conifer proportion was associated with higher FF and soil C:N ratios. Soil texture had no significant impact on FF or mineral SOC stocks but did influence carbon partitioning among SOM fractions and soil C:N ratios. In summary, while large herbivores can impact soil C‐storage characteristics in open temperate ecosystems, we find that, on decadal timescales, tree species composition and diversity and soil texture exert greater control over these parameters in a temperate primeval forest. Therefore, large ungulate exclusion is unlikely to provide soil C storage benefits in similar forest systems.