Carbon balance shift in mountain peatlands along a gradient of grazing disturbance in the tropical Andes (Colombia)

Abstract

High-elevation cushion peatlands are typical ecosystems of the Andes above 4000 m of altitude, with an important role in hydrology and global carbon sequestration. In Tropical Andean context, grazing livestock is one of the main threats to cushion peatlands, altering the vegetation and the storage carbon function. The aim of this research is to understand how grazing influences cushion peatland functioning by identifying ecological thresholds for carbon balance process. The study was carried out in four Andean peatlands in the northern part of Colombian Andes during 2019–2020. We established 30 plots of 1 m2 where water table level, vegetation cover, and grazing disturbance were monitored. We also measured CO2 fluxes using an infrared gas analyzer connected to a closed static chamber, which registered net ecosystem exchange and respiration data. Considerable variation in the conservation status of Distichia muscoides cushions was found within the sampled peatlands, reflecting an heterogeneous signal of grazing disturbance that is evident at the plot-specific scale. Decreasing water table level was related with changes in dominant vegetation, from compact cushion species to grasses proliferation, exacerbating disturbance effects and carbon emissions. Mixed-effects logistic regression models showed a carbon balance shift, from CO2 sink to net emitter, in plots with high disturbance intensity and low D. muscoides cover. This study provides information for a better understanding of mountain peatlands functioning in the Tropical Andes and underlines the key role of D. muscoides cushions and the water table in carbon balance shift.