Evidence of Increased Soil Organic Matter Accumulation in a Tropical Alpine Wetland After Cattle Removal

Tropical alpine ecosystems, regionally known as "páramos", are key to healthy socio-environments in the Andean region because of the environmental services they provide. Rivers and streams originating in these ecosystems supply water to most Andean cities, agricultural activities, and hydropower generation. Ranging from the border of the tree line to the permanent snow line, these ecosystems develop in valleys and plains of glacial origin and include small lakes, peat bogs, wet grasslands, shrublands, and dispersed short-height forest patches (Buytaert et al. 2006). At sites with low disturbances, soil organic matter (SOM) content is high, commonly above 40% (Buytaert et al. 2005). In addition, they are important biodiversity hotspots due to the high level of endemism of species adapted to this unique environment.

The ecological functions of tropical alpine ecosystems are threatened by increasing pressures due to climate change, agriculture, mining, and forestry. Furthermore, scientific knowledge of these ecosystems is low relative to other tropical ecosystems. Therefore, conservation and restoration of degraded portions of these ecosystems is critical. A common management practice to enhance restoration in these ecosystems is the removal of stressors through land purchase and posterior designation as conservation sites. However, how the removal of disturbances in tropical alpine wetlands improve ecosystem functions and services is poorly reported in scientific literature, preventing the overall evaluation of this practice and the proper establishment of goals for restoration, management, and monitoring. In this study, two peat cores from an ongoing carbon sequestration project in a páramo that were collected in previously grazed areas, were examined. The objective was to evaluate the effect that cattle removal has had on SOM accumulation.

Figure 1.

Downhill view of the studied peatland in northeast Columbia. The bottom of the picture shows the characteristic "frailejones" (Espeletia sp.) of the paramo. These are indicating the borderline between uplands and the peatland near the coring sites.

The cores were collected in northeast Colombia, at the northern end of the Andean Cordillera (6°40′54″ N, 75°40′37.6″ W), at approximately 3200 m a.s.l. This site is a 40.5 ha peatland that had developed from the continued build-up of organic matter in a relatively small mountaintop canyon (Figure 1). Mean surface water pH during core collection in June 2015 was 4.7 (n = 17). This wetland is rainwater feed and is also the headwater of two creeks that run on each end of the valley to feed watersheds that provide drinking water for more than 1 million people in the Aburrá Metropolitan Area and nearby townships. Water from this and surrounding headwaters is also used for hydropower generation. Purchase of the site for conservation was completed in 1997. Prior to this date, the side slopes that drained to the valley where the peatland is sited, were used by native peoples for extensive cattle grazing and reportedly included the shallow peat deposits near the side slopes where the cores were collected. No official record exists about the history of pasturing in the area, however, elderly locals date back grazing activity to at least three generations.

Cores were collected using a universal core head sediment sampler (Watermark™) with 6.5 cm I.D. polycarbonate barrels. Cores were collected in June (core A) and October (core B) of 2015. During continuous monitoring from June 2015 to April 2016, mean water table next to the core A extraction site was 4.3 cm below the soil surface and ranged from 9.8 cm below the surface to 1.3 cm above it. Next to core B, mean water table was 2.4 cm below the surface and ranged from 7.2 cm below to 8.6 cm above. Vegetation in the wetland is dominated by Calamagrostis effusa and Orthrosanthus sp. Sphagnum rubellum, a characteristic plant of acidic peatlands, represents less than 5% of relative abundance (unpub. data).

After extraction, cores were sectioned in 2-cm depth intervals, packed and sealed in separate bags for transportation. Once in the lab, samples were dried at 55°C...