A context-dependent response of soil carbon and nitrogen to grazing exclusion: Evidence from a global meta-analysis

Abstract

Grazing exclusion (GE) is commonly used worldwide in the management of degraded grasslands. While the effects of GE on soil organic carbon (SOC) and soil total nitrogen (STN) are intensively studied, little consensus has emerged due to highly variable background conditions. Drawing on 4081 observations from over 200 experiments worldwide, we applied a hierarchical meta-analysis to evaluate the effect of GE on SOC and STN. Overall, GE significantly increased SOC (14.74%) and STN (28.75%) compared to traditional grazing. However, the effect was mainly dependent on GE duration, site elevation and the mean annual precipitation. The improvement in SOC and STN were greatest when the duration of GE exceeded 10 years and the mean annual temperature, precipitation and elevation ranged between 0°C and 10 °C, less than or equal to 300 mm, and 1500 m–2500 m, respectively. In temperate and desert grasslands, long-term GE (>10 years) improved SOC and STN, whereas in meadow grasslands, short-term GE (≤5 years) contributed the most to their improvement. Long-term GE (>10 years) had a significant positive effect on SOC and STN in historically lightly and heavily grazed areas, but not in historically moderately grazed areas. As the response of SOC and STN under GE duration can vary from positive to negative based on different conditions, an appropriate GE duration implementation strategy should be developed in a context-dependent manner during future restoration of degraded grasslands.