The opulence of the rubber barons could only be exceeded by their brutality.
Wild Hevea trees, like all primary rainforest trees are widely dispersed, an adaptation that protects species from the South American leaf blight which easily spreads through and decimates plantations.
Thus to make a profit, barons had to acquire control over huge tracts of land. Most did so by by hiring their own private armies to defend their claims, acquire new land, and capture native laborers.
Labor was always a problem so barons got creative. One baron created a stud farm, enslaving 600 Indian women whom he bred like cattle.
Other barons like Julio Cesar Arana simply used terror to acquire and hold on to Indian slaves. Indians captured usually submitted because resistance only meant more suffering for the families.
Young girls were sold as whores, while young men were bound, blindfolded, and had their genitals blasted off. As the Indians died, production soared: in the 12 years that Arana operated on the Putumayo River in Colombia, the native population fell from over 30,000 to less than 8,000 while he exported over 4000 tons of rubber earning over $75 million.
The only thing that stopped the holocaust was the downfall of the Brazilian rubber market.
Extracted from http://www.mongabay.com/10rubber.htm