SOM and Biomass C Stocks in Degraded and Undisturbed Andean and Coastal Nothofagus Forests of Southwestern South America

Grazing and over-exploitation can severely degrade soil in native forests. Considering that productivity in ecosystems is related to soil organic matter (SOM) content and quality, the objectives of this study were to: (1) determine the influence of degraded (DEF), partly-degraded (PDF), and undisturbed (UNF) Nothofagus forests on the stocks of carbon (C) in tree biomass and SOM; (2) evaluate fractions of SOM as indicators of sustainable management; and (3) use the Century model to determine the potential gains of soil organic C (SOC). The forests are located in the Andes and Coastal mountains of southern Chile. The SOM was fractionated to separate the light fraction (LF), macroaggregates (>212 mu m), mesoaggregates (212-53 mu m), and microaggregates (<53 mu m). In two measurement periods, the SOC stocks at 0-20 cm and 20-40 cm depths in macroaggregates were on average 100% higher in the Andean UNF, and SOC was over twice as much at 20-40 cm depth in Andean DEF. Century simulations showed that improved silvopastoral management would gradually increase total SOC in degraded soils of both sites, especially the Ultisol with a 15% increase between 2016 and 2216 (vs. 7% in the Andisol). Greater SOC in macroaggregates (p < 0.05) of UNF indicate a condition of higher sustainability and better management over the years.