The deforestation of high diversity tropical ecosystems has been mainly due to agricultural expansion, cattle ranching, timber extraction, and urban expansion; and these activities have important consequences for the global carbon budget, biodiversity loss, and degradation of ecosystem services (Lambin et al 2003). In the last 10–20 years, much of tropical deforestation has been attributed to the growing economies of developing countries, particularly China. The increasing wealth in these countries is partly reflected by increased global demand for meat, which has been directly correlated with the expansion of croplands for soybean production (animal feed) and grasslands for meat production in South America (Aide et al 2013). The deforestation associated with these land changes in South America is on the scale of millions of hectares, which makes it easy to detect, but the increase in disposable income in developing countries can also stimulate other causes of tropical deforestation that are much more difficult to detect, specifically gold mining.

Global gold production has increased from ~2445 metric tons in 2000 to ~2770 metric tons in 2013 (USGS 2014). This increase has been driven by personal consumption (e.g. jewelry), particularly in China and India (World Gold Council 2012, Cremers et al 2013), and uncertainty in global financial markets (e.g. value of the dollar and euro) (Shafiee and Topal 2010). This increase in demand over the last 13 years has been paralleled by a dramatic increase in price (Shafiee and Topal 2010). Over the last thirteen years, the price of gold has increased from $250/ounce in 2000 to $1300/ounce in 2013 (figure 1(a); World Gold Council 2012). This rise in global demand and the price of gold have stimulated new gold mining activities by multinational companies and small-scale gold miners throughout the world (Bury 2004, Creek 2009).

Figure 1. (a) Global price of gold per ounce (USD) from January 1980 to May 2014 (World Gold Council 2012). (b) Gold production ( x 103 ounces) in Latin American countries from 1970 to 2010 (Brown et al 2010) Download figure: Standard image High-resolution image Export PowerPoint slide

The high price of gold has made it feasible to extract gold from areas that were not previously profitable for mining, including low-grade deposits underneath tropical forests (Swenson et al 2011). In many cases, the mining of these deposits is characterized by unorganized occupation of lands and uncontrolled mining operations, causing significant forest loss and environmental impacts (Hentschel et al 2002, Villegas et al 2012). Specifically, gold mining impacts forests by removing vegetation for mining pits, transportation access (roads, railways), and settlements. Small-scale mining operations also remove gallery forest to extract alluvial deposits of gold by using high-pressure water jets to remove and process the soil (Almeida-Filho and Shimabukuro 2002). Moreover, although gold mining is usually temporary and occupies relatively small areas, mining effects and impacts are persistent. Long-lasting environmental effects of gold mining include air, soil and water pollution from arsenic, cyanide, and mercury (Eisler and Wiemeyer 2004, Veiga et al 2006). Pollution and sediments from gold mining activities travel long distances through rivers and tributaries negatively affecting water quality and access for humans, fish and other wildlife (Uryu et al 2001). Furthermore, forest recovery after mining activities is significantly slower when compared to regeneration after other land uses (e.g. agriculture, pasture) (Peterson and Heemskerk 2002).

As mining sites often occur in remote locations, they frequently coincide with protected areas (PAs) (Durán et al 2013) or areas of high biodiversity (Villegas et al 2012). Deforestation due to gold mining has become a major threat to some of the most remote and better-conserved old-growth forests in tropical South America (Peterson and Heemskerk 2002, Asner et al 2013). For example, the department of Madre de Dios (Peru), one of the most biologically rich areas on Earth, lost 400 km2 of forest due to gold mining between 1999 and 2012 (Asner et al 2013). In Suriname, estimates indicate that gold miners clear between 48 km2 and 96 km2 of old-growth forest per year (Peterson and Heemskerk 2002).

Although the environmental costs of gold mining are high, it is a major contributor to the economies of industrialized and developing countries, as well as a principal source of income for many people. In Latin American, the gold mining sector is growing rapidly (Bebbington and Bury 2013), with production increasing from ~414 000 ounces to 542 000 ounces of gold in the last decade (figure 1(b)). In Peru, large-scale mining contributed an average of 6% to the GDP between 2000 and 2010 (World Gold Council 2012). In Colombia, the gold mining sector generates more than 140 000 permanent jobs and an unknown number of informal employments in small-scale mining operations (International Labour Organization 2008). In addition, artisanal and small-scale gold mining employed ~200 000 people in the Brazilian Amazon in 2008 (Sousa et al 2011). In Suriname, gold mining supports the livelihood of more than 60 000 people (~12% of the population) (Cremers et al 2013).

As the global demand and price for gold continues to increase (Shafiee and Topal 2010), gold mining activities will likely continue to increase in the tropical forests of South America. Given this current gold rush, the known impacts of gold mining, and the presence of gold mining in remote areas of high biodiversity, we urgently need better information on the distribution and impacts of gold mines in tropical forests. To address these challenges, we identified potential gold mining sites below 1000 m within the tropical moist forest biome (TMFB) of South America. We then estimated forest cover change between 2001 and 2013 using maps derived from MODIS MOD13Q1 imagery (250 m resolution). Specifically, we addressed the following questions: (1) what was the extent of forest change associated with gold mining between 2001 and 2013 in tropical forests of South America? (2) What were the trends of forest change (e.g. deforestation and reforestation) before and after the International Financial Crisis of 2007–2008? (3) Where are the hotspots of gold mining deforestation? and (4) Is gold mining occurring within or around PAs?