Soil Carbon Baseline Assessment in the Andes and Challenges Posed by Climate Driven Land Use Dynamics.

A significant warming in the Andes after 1979 (0.32 -0.34 ^oC/decade) is documented.  Likely prompted by an increased incidence of vectors and pests, which affect crop productivity and diversity, farmers have responded by an upward migration of croplands, encroaching upon rangelands/peatlands.  As carbon accumulation and sequestration in Andean soils are scarcely documented, carbon contents (CC), carbon stocks (CS), and stability were determined in five agroecologies in Peru, covering the arid Pacific coast, the Andean high plateau, and the eastern tropical highland rainforest.  It was hypothesized that CS and stability varied with land use and altitudinal gradient. Results showed that the rangelands/peatlands presented the highest (p > 0.05) CC (634 – 832 g kg^–1) as well as the largest CS (233 - 306 Mg ha^–1). Potato-based cropping systems presented low CC (68 g kg^–1) and CS (47 Mg ha^–1) whereas shaded coffee and alfalfa gave intermediate levels (~83 Mg ha^–1). Rangelands/peatlands showed the lowest carbon recalcitrance, as evidenced by EPR, LIFS and ¹³C-NMR. Results suggest that diversified crops/livestock production systems are more stable for carbon stocks, which might help farmers in adapting to climate change. Preliminary estimates, based on average CS under present land uses, crop models fed with IPCC scenarios to map areas for potato production in Peru and Bolivia by 2050, and imagery mapping of actual land use indicate that potential loss of C stocks in both countries brought about by land use change from rangelands to croplands is in the order of 14 Tg (14 x 10¹² g).  More in-depth spatial assessment over a range of land use historic data and the use of modeling tools are required.  An international network of research and training institutions to assess CS and to model C dynamics under climate variability and change has been established.