Forest Loss Dynamics and Impacts from Gold Mining in Amazonia

Amazonian rainforests are home to Earth’s largest reservoir of biodiversity, providing crucial ecosystem services and storing approximately 17% of all global terrestrial carbon. Today, these forests are experiencing rapid, unprecedented changes due to climate impacts and anthropogenic disturbances. In recent decades, the region has experienced marked variability in deforestation, and after a long period of increase, the deforestation rates in countries like Brazil have sharply declined in recent years. However, little is known about the forest trends and the impact of different drivers in other Amazonian countries. The aim of this thesis, therefore, is to better understand and examine the current dynamics of forest loss across Amazonia and how intensive land uses such as gold mining influence forest loss, nutrient cycling and recovery patterns. Using remote sensing coupled with field observations, this research highlights new spatial patterns in Amazonian forest loss which point to a more complex pattern where new smaller-scale drivers of forest loss are becoming progressively more important (Chapter 2). The expansion of small-scale events were primarily driven by gold mining activities, particularly in northern Amazonia, with underestimation of forest loss occurring at sites driven by a mosaic of small-scale clearings (Chapter 3). Nutrient depletion was found to be the most important factor driving low biomass recovery in previously mined areas, with mercury contamination being of secondary importance (Chapters 4 and 5). Overall, small-scale gold mining can severely impair the forest’s ability to recover at abandoned mining pits and tailing ponds while recovery rates of woody biomass on the overburden zone were comparable to other secondary forests across the Neotropics following abandonment of pastures and agriculture (Chapter 5). Gold mining across the Amazon could potentially result in ~90,000 t C yr-1 less carbon being accumulated in relation to what would have accumulated under agriculture/pasture. Important conclusions from this work suggests that (1) national deforestation statistics need to include these small-scale events which are currently excluded from important official estimates such as Brazil’s PRODES, and (2) active rehabilitation and restoration are required in order to assist the disrupted successional processes at gold mining sites. The results presented here highlight the vulnerability of Amazonian forests to newer, more intense types of land uses such as small-scale gold mining.