In 2011, 51 people from indigenous tribes were killed in Brazil – and nearly half those deaths have been linked to battles over land.

This is not casual violence, but planned and paid for: a devastating side-effect of a big new drive to exploit Brazil's natural resources which has pushed industrial farming and mining into areas of marginal land and protected rainforest.

Last week, a shocking New York Times report told of landowners shipping in gunmen by truck and motorbike to stop protests by the impoverished Guarani tribe in a disputed area near Brazil's border with Paraguay.

Decades of abuse

All over Brazil indigenous tribes have been under assault for generations, as farming and mining have eaten away at their traditional lands.

The Guarani in Mato Grosso do Sul state have been under pressure since European colonists arrived 500 years ago. But their present troubles date back to the 1930s, when they were forced into small reserves so that their land could be granted to settlers. While the region has become wealthy, the Guarani have suffered poverty, malnutrition and enslavement as bonded labour. The Dourados reserve, where 12,000 Guarani live in appalling conditions, is too small for families to grow enough crops to feed themselves. Violence and suicide are epidemic.

The Guarani land is wanted for massive soya bean farms, part of Brazil's push for more biofuels. Last November, after tribal leader Nísio Gomes led a protest squat on a soya bean farm, hired pistoleiros descended on the camp, beat adults and children and killed him, taking away his corpse.

Government can help, if it wants to

Brazil's government has been taking steps to protect its indigenous people. The deputy attorney-general has spoken of the "tragedy" of Dourados, and in 2009 the High Court expelled non-indigenous rice farmers from the lands of 20,000 people – mainly those of the Macuxi tribe in the northern state of Roraima. At the beginning of June President Dilma created two new nature reserves, as well as seven territories for indigenous peoples.

But sceptics have said the move is a sop to the conservation lobby. It echoes (but hardly matches) a government move on the eve of the first Rio summit, 20 years ago. Then, to save Yanomami tribespeople under lethal assault from gold miners, the government created a 96,000 sq km (37,000 sq miles) reserve in the Amazon.

As recent battles over Brazil's new forestry code showed, President Dilma and her government are disturbingly open to the demands of the commercial forces that want to exploit protected areas.

Brazil has made great progress in recent years towards protecting its environment and ensuring the rights and fragile livelihoods of indigenous people. All those advances are now under threat – and those who complain may die.

Take action: Join Avaaz's call to protect indigenous people and the environment from the effects of Brazil's massive dam-building project.

Learn more: Survival International has maps and information on the 150 million indigenous peoples living in fear across the world.