Impact of Extensive Grazing on Supporting and Regulating Ecosystem Services of Mountain Soils

Abstract

Livestock grazing impacts the ecosystems of high mountains and adjacent low-elevation regions as a result of the physical, chemical, and hydrological connectivity of soil. In particular, grazing may alter the ecosystem services provided by soil, such as carbon and organic matter accumulation, carbon storage, and water infiltration. The present study evaluated the relative contents of soil organic matter (SOM) and soil organic carbon (SOC) on soil in a humaninduced grassland and an frequently grazed Abies religiosa (Kunth) Schltdl. & Cham. forest in Nevado de Toluca, Mexico. It assessed carbon stocks in 2 different soil layers (0–5 cm and 5–25 cm), as well as soil compaction and water infiltration in both land uses. Results showed slightly lower SOM (21.7%) and SOC (12.6%) in soils on which livestock were grazed than in forest soils (25.7% for SOM and 14.65%, for SOC) at both depths and a greater bulk density of livestock soils (0.86 g cm3 ) than of forest soils (0.73 g cm3 ), particularly in the 0–5- cm layer (0.88 g cm3 ) of livestock soils. More than 40 years of livestock grazing has clearly impacted the capacity of soils to accumulate organic matter and organic carbon. However, carbon stocks and water infiltration were not significantly affected, as low carbon accumulation was compensated by changes in soil bulk density. These results indicate that extensive livestock ranching and resource conservation are not necessarily mutually exclusive in the study site. Direct and indirect mechanisms involved in the provision of the evaluated regulating services should be further studied, taking into account the highly variable social and environmental conditions of Nevado de Toluca. Management policies should also aim to maintain an equilibrium between livestock rancher needs and conservation of supporting and regulating ecosystem services that are highly relevant to the functioning of mountain ecosystems.